CN117735502A - Preparation method and application of lithium iron phosphate precursor - Google Patents
Preparation method and application of lithium iron phosphate precursor Download PDFInfo
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Abstract
The invention relates to the field of lithium ion battery anode materials, in particular to a preparation method and application of a lithium iron phosphate precursor. The method comprises the following steps: mixing an iron source, a phosphorus source and an oxidant, and then carrying out precipitation reaction; carrying out first washing on the precipitation slurry; mixing the first clear liquid and the second clear liquid; adding an oxidant and an iron source into the mixed clear liquid; mixing the precipitate slurry and the slurry A, and then performing second washing; performing a first aging reaction on the slurry C, and adding phosphoric acid into the slurry C in the first aging reaction process; performing a second aging reaction on the slurry D, and adding phosphoric acid into the slurry D in the second aging reaction process; slurry E and slurry F were mixed and then subjected to a mild second wash. According to the method, the prepared lithium iron phosphate precursor is used for preparing the lithium iron phosphate, so that the compaction density and capacity of the lithium iron phosphate can be improved, and the method has the advantages of environmental friendliness and low cost.
Description
Technical Field
The invention relates to the field of lithium ion battery anode materials, in particular to a preparation method and application of a lithium iron phosphate precursor.
Background
Lithium iron phosphate is considered as one of the competitive lithium ion battery electrode materials due to its excellent electrochemical properties, good safety, low cost, and the like. However, lithium iron phosphate batteries also suffer from unavoidable drawbacks such as low energy density. Solving the problem of low energy density can be improved by increasing gram volume and compaction density; at present, the gram capacity of the lithium iron phosphate material exceeds 160mAh/g and approaches to the theoretical capacity of 170mAh/g, so that the lifting space is not large; the compaction density of the lithium iron phosphate anode material is improved, most of researches at present only adopt a physical mechanical method to mix solid lithium iron phosphate in the preparation process of lithium iron phosphate, but the general compaction effect is not obvious, uneven mixing can be caused, small particles cannot be effectively filled, and the obtained product possibly has larger compaction density difference of different batches.
In view of this, the present invention has been made.
Disclosure of Invention
The invention aims to provide a preparation method and application of a lithium iron phosphate precursor, wherein the prepared lithium iron phosphate precursor has moderate size particles, lithium iron phosphate mixed with the particle size can be directly prepared, and the compacted density and capacity of the lithium iron phosphate are high.
In order to achieve the above object of the present invention, the following technical solutions are specifically adopted:
one aspect of the invention relates to a method for preparing a lithium iron phosphate precursor, comprising the following steps:
(a) Mixing an iron source, a phosphorus source and an oxidant, and then carrying out precipitation reaction to obtain precipitation slurry; performing first washing on the precipitation slurry to obtain a first clear liquid;
(b) Mixing the first clear liquid and the second clear liquid to obtain a mixed clear liquid; adding the oxidant and the iron source into the mixed clear liquid to obtain slurry A; mixing the precipitation slurry with the slurry A, and then performing second washing to obtain a washing filter cake;
(c) Adding water into the first filter cake to prepare slurry C with the concentration of 15-20wt% and slurry D with the concentration of 5-10wt%;
(d) Performing a first aging reaction on the slurry C, and adding phosphoric acid into the slurry C in the first aging reaction process to obtain slurry E; performing a second aging reaction on the slurry D, and adding phosphoric acid into the slurry D in the second aging reaction process to obtain slurry F;
the content of phosphoric acid in the slurry E is 3-5 wt%;
the content of phosphoric acid in the slurry F is 0.1-0.3 wt%;
(e) Mixing the slurry E and the slurry F, and then performing mild reaction and second washing to obtain the second clear liquid and a second-stage filter cake; and calcining the secondary filter cake to obtain the lithium iron phosphate precursor.
According to the preparation method of the lithium iron phosphate precursor, the prepared lithium iron phosphate precursor is used for preparing the lithium iron phosphate, so that the compaction density and capacity of the lithium iron phosphate can be improved, and the preparation method has the advantages of being environment-friendly and low in cost.
The invention also relates to a lithium iron phosphate positive electrode material which is mainly prepared from the lithium iron phosphate precursor prepared by the preparation method of the lithium iron phosphate precursor.
In another aspect, the invention also relates to a lithium ion battery, which comprises the lithium iron phosphate positive electrode material.
Compared with the prior art, the invention has the beneficial effects that:
(1) According to the preparation method of the lithium iron phosphate precursor, the precipitation section has the advantages that the content of phosphorus element in washing water and filtrate is low, and the size of the generated ferric phosphate particles is different after the lithium iron phosphate precursor is mixed with normal precipitation slurry; the aging working section controls the addition amount of phosphoric acid to be different, so that the supersaturation degree of amorphous ferric phosphate in the crystal form conversion process is different, the particle size difference is further increased, and the method is used for preparing lithium iron phosphate and can improve the compaction density and capacity of the lithium iron phosphate.
(2) The preparation method of the lithium iron phosphate precursor can recycle the washing water and the filtrate generated in the precipitation and ageing working section, thereby reducing the preparation cost of the lithium iron phosphate precursor and being environment-friendly.
(3) The lithium iron phosphate anode material provided by the invention has the advantages of reasonable matching of lithium iron phosphate with different particle sizes, high compaction density and high capacity.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a preparation method of a lithium iron phosphate precursor provided by an embodiment of the invention;
FIG. 2 is a scanning electron microscope image of the iron phosphate and lithium iron phosphate of the precipitation section and the aging section of example 1;
FIG. 3 is a scanning electron microscope image of iron phosphate and lithium iron phosphate of the precipitation section and the aging section of comparative example 1.
Detailed Description
The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and detailed description, but it will be understood by those skilled in the art that the examples described below are some, but not all, examples of the present invention, and are intended to be illustrative of the present invention only and should not be construed as limiting the scope of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
One aspect of the invention relates to a method for preparing a lithium iron phosphate precursor, comprising the following steps:
(a) Mixing an iron source, a phosphorus source and an oxidant, and then carrying out precipitation reaction to obtain precipitation slurry; performing first washing on the precipitation slurry to obtain a first clear liquid;
(b) Mixing the first clear liquid and the second clear liquid to obtain a mixed clear liquid; adding the oxidant and the iron source into the mixed clear liquid to obtain slurry A; mixing the precipitation slurry with the slurry A, and then performing second washing to obtain a washing filter cake;
(c) Adding water to the one-washing filter cake to prepare slurry C with the concentration of 15-20wt% (such as 15-16wt%, 17-18wt%, 19-wt% or 20wt%) and slurry D with the concentration of 5-10wt% (such as 5-6wt%, 7-7wt%, 8-9wt%, 9-wt% or 10wt%), respectively;
(d) Performing a first aging reaction on the slurry C, and adding phosphoric acid into the slurry C in the first aging reaction process to obtain slurry E; performing a second aging reaction on the slurry D, and adding phosphoric acid into the slurry D in the second aging reaction process to obtain slurry F;
the content of phosphoric acid in the slurry E is 3wt% -5 wt% (such as 3wt%, 4wt% or 5 wt%);
the content of phosphoric acid in the slurry F is 0.1wt% -0.3 wt% (for example, 0.1wt%, 0.2wt% or 0.3 wt%);
(e) Mixing the slurry E and the slurry F, and then performing mild reaction and second washing to obtain the second clear liquid and a second-stage filter cake; and calcining the secondary filter cake to obtain the lithium iron phosphate precursor.
According to the preparation method of the lithium iron phosphate precursor, washing water and filtrate obtained in a precipitation working section and a precipitation working section are mixed and then mixed with precipitation slurry to carry out primary filter pressing washing, the content of phosphorus in the filtrate and the washing water is low, and under the condition of low supersaturation degree of solution, growth power after nucleation of crystal nucleus is small, at the moment, crystal growth is mainly affected by thermodynamic, so that the reaction is carried out at the same temperature to carry out precipitation reaction, particles are small, and amorphous ferric phosphate with different particle sizes is obtained after the mixture is mixed with normal precipitation slurry.
Since the aging working section aims at crystal form conversion, in the process, amorphous ferric phosphate can be recombined to form ferric phosphate with an orthorhombic crystal system, so that the advantages of the size particles of the amorphous ferric phosphate are weakened in the aging working section, the adding amount of phosphoric acid in the aging working section is changed, so that the supersaturation degree is different during crystal form conversion, the crystal nucleation and growth speed difference are caused, the slurry concentration is changed, the difference is improved, the particle size difference of a mixed sample after the crystal form conversion is more obvious, the particle size of small particles is 50-100 nm, and the particle size of large particles is 200-300 nm.
The size of the lithium iron phosphate material depends on the size of iron phosphate to a great extent, and the size of the iron phosphate particles prepared by the preparation method of the lithium iron phosphate precursor is moderate, so that the lithium iron phosphate material can be directly used for preparing lithium iron phosphate, and the lithium iron phosphate mixed with the size of the particles can be prepared, and has high compaction density and high capacity.
Further, the content of the phosphorus element in the mixed clear liquid is 0.1wt% to 0.5wt% (e.g., 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt% or 0.5 wt%).
Further, the filter cake comprises: first particles having a particle size of 200 to 500nm (e.g., 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, or 500 nm) and second particles having a particle size of 10 to 50nm (e.g., 10nm, 20nm, 30nm, 40nm, or 50 nm).
Further, in the step (a), the iron source, the phosphorus source and the hydrogen peroxide are mixed according to the molar ratio of (1-1.3): 1: (0.5-1) (e.g., 1:1:1, 1.1:1:0.8, 1.2:1:0.6, or 1.3:1:0.5).
Further, in step (a), the iron source is added in the form of an iron source aqueous solution.
Further, the concentration of the iron source aqueous solution is 40 to 90g/L (for example, 40g/L, 50g/L, 60g/L, 70g/L, 80g/L or 90 g/L).
Further, the iron source includes: at least one of ferrous sulfate, ferrous oxalate or ferrous chloride.
Further, in step (a), the phosphorus source is added in the form of an aqueous solution of the phosphorus source.
Further, the concentration of the phosphorus source aqueous solution is 2wt% to 5wt% (e.g., 2wt%, 3wt%, 4wt%, or 5 wt%).
Further, the phosphorus source comprises: at least one of phosphoric acid, monoammonium phosphate or diammonium phosphate.
Further, the oxidizing agent includes: hydrogen peroxide.
Further, in the step (b), the iron source, the phosphorus in the mixed clear solution and the oxidant are mixed according to the molar ratio of (1-1.3): 1: (0.5-1) (e.g., 1:1:0.5, 1.1:1:0.7, 1.2:1:0.8, or 1.3:1:1).
Further, in the step (b), the volume ratio of the precipitated slurry to the slurry A is 100: (5-15) (e.g., 100:5, 100:8, 100:10, 100:13, or 100:15).
Further, in the step (E), the mixing volume ratio of the slurry E to the slurry F is (0.1 to 0.3): 1 (e.g., 0.1:1, 0.2:1, or 0.3:1).
Further, the solids content of the precipitation slurry is 7wt% to 10wt% (e.g., 7wt%, 8wt%, 9wt%, or 10 wt%).
Further, the slurry a has a solids content of 7wt% to 10wt% (e.g., 7wt%, 8wt%, 9wt%, or 10 wt%).
Further, the temperature of the first aging reaction is 30 to 70 ℃ (e.g., 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃, or 70 ℃).
Further, the time of the first aging reaction is 30-120 min (for example, 30min, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min or 120 min).
Further, the temperature of the second aging reaction is 30 to 70 ℃ (e.g., 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃, or 70 ℃).
Further, the second aging reaction is performed for 30-120 min (e.g., 30min, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min, or 120 min).
Further, the temperature of the heat preservation is 85 to 95 ℃ (e.g., 85 ℃, 87 ℃, 89 ℃, 91 ℃, 93 ℃ or 95 ℃).
Further, the time of the heat preservation is 0.5-4 h (for example, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h or 4 h).
The invention also relates to a lithium iron phosphate positive electrode material which is mainly prepared from the lithium iron phosphate precursor prepared by the preparation method of the lithium iron phosphate precursor.
Further, the preparation method of the lithium iron phosphate positive electrode material comprises the following steps:
and mixing the prepared ferric phosphate with a lithium source, a carbon source and an additive, and then sanding, spray drying and sintering.
Further, the lithium source is at least one of lithium carbonate, lithium dihydrogen phosphate or lithium hydroxide.
Further, the carbon source is at least one of glucose, white granulated sugar or PEG 6000.
Further, the additive is at least one of titanium dioxide or vanadium pentoxide.
Further, the molar ratio of Li in the lithium source to P in the phosphorus source is 0.99-1.01, and the addition amount of the carbon source and the additive is 10-20 wt% and 0.05-0.3 wt% of the ferric phosphate.
Further, the particle diameter after sand grinding is 0.35-0.5 mu m.
Further, the sintering temperature is 700-800 ℃; the sintering time is 4-12 h.
Further, the compacted density of the lithium iron phosphate positive electrode material is 2.45-2.55 g/cm 3 。
In another aspect, the invention also relates to a lithium ion battery, which comprises the lithium iron phosphate positive electrode material.
Embodiments of the present invention will be described in detail below with reference to specific examples and comparative examples.
Example 1
The preparation method of the lithium iron phosphate precursor provided in the embodiment, as shown in fig. 1, includes the following steps:
(1) Mixing 500mL of ferrous sulfate, phosphoric acid and hydrogen peroxide, and performing precipitation reaction to obtain a precipitation slurry, wherein the molar ratio of the ferrous sulfate to the phosphoric acid to the hydrogen peroxide is 1:1:0.75; the ferrous sulfate contains 60g/L of ferrous sulfide, the phosphoric acid contains 3% of phosphorus, and the solid content of the precipitation slurry is 8wt%;
(2) Carrying out filter pressing washing on the precipitation slurry to obtain clear liquid 1;
(3) Mixing the clear solution 1 and the clear solution 2 to obtain a mixed clear solution, wherein the content of phosphorus element in the mixed clear solution is 0.2wt%, adding ferrous sulfate and hydrogen peroxide into the mixed clear solution, and the molar ratio of the phosphorus in the mixed clear solution to the ferrous sulfate and the hydrogen peroxide is 1:1:0.75 to obtain slurry A; slurry A has a solids content of 8%;
(4) The volume ratio of the precipitated slurry to the slurry A is 100:8, mixing to obtain mixed slurry B;
(5) The mixed slurry B is subjected to filter pressing and washing to obtain a washing filter cake;
(6) Adding water into a filter cake to prepare slurry C with the concentration of 18wt% and slurry D with the concentration of 8wt%;
(7) Adding 4wt% of 85% phosphoric acid into the slurry C at 60 ℃ to perform a first aging reaction, wherein the first aging reaction time is 2 hours, so as to obtain slurry E; adding 0.2wt% of 85% phosphoric acid into the slurry D for a second aging reaction, wherein the second aging reaction time is 30min, so as to obtain slurry F;
(8) After both the slurry E and the slurry F become white, the volume ratio of the slurry E to the slurry F is 0.2:1, mixing, preserving heat for 1h at 90 ℃, and then performing filter pressing washing to obtain clear liquid 2, and calcining a filter cake to obtain anhydrous ferric phosphate.
Example 2
The preparation method of the lithium iron phosphate precursor provided in the embodiment, as shown in fig. 1, includes the following steps:
(1) Mixing 500mL of ferrous sulfate, phosphoric acid and hydrogen peroxide, and performing precipitation reaction to obtain a precipitation slurry, wherein the molar ratio of the ferrous sulfate to the phosphoric acid to the hydrogen peroxide is 1.3:1:1, a step of; the ferrous sulfate contains 60g/L of ferrous sulfide, the phosphoric acid contains 3% of phosphorus, and the solid content of the precipitation slurry is 10wt%;
(2) Carrying out filter pressing washing on the precipitation slurry to obtain clear liquid 1;
(3) Mixing the clear solution 1 and the clear solution 2 to obtain a mixed clear solution, wherein the content of phosphorus element in the mixed clear solution is 0.5wt%, ferrous sulfate and hydrogen peroxide are added into the mixed clear solution, and the molar ratio of the phosphorus in the mixed clear solution to the ferrous sulfate and the hydrogen peroxide is 1:1.1:0.75 to obtain slurry A; slurry A has 7% solids;
(4) The volume ratio of the precipitated slurry to the slurry A is 100:1, mixing to obtain mixed slurry B;
(5) The mixed slurry B is subjected to filter pressing and washing to obtain a washing filter cake;
(6) Adding water into a filter cake to prepare slurry C with the concentration of 20wt% and slurry D with the concentration of 10wt%;
(7) Adding 5wt% of 85% phosphoric acid into the slurry C at 65 ℃ to perform a first aging reaction, wherein the first aging reaction time is 1.5h, so as to obtain slurry E; adding 0.1wt% of 85% phosphoric acid into the slurry D for a second aging reaction, wherein the second aging reaction time is 1h, so as to obtain slurry F;
(8) After both the slurry E and the slurry F become white, the volume ratio of the slurry E to the slurry F is 0.1:1, mixing, preserving the temperature at 85 ℃ for 4 hours, and then performing filter pressing washing to obtain clear liquid 2, and calcining a filter cake to obtain anhydrous ferric phosphate.
Example 3
The preparation method of the lithium iron phosphate precursor provided in the embodiment, as shown in fig. 1, includes the following steps:
(1) Mixing 500mL of ferrous sulfate, phosphoric acid and hydrogen peroxide, and performing precipitation reaction to obtain a precipitation slurry, wherein the molar ratio of the ferrous sulfate to the phosphoric acid to the hydrogen peroxide is 1:1:0.5; the ferrous sulfate contains 60g/L of ferrous sulfide, the phosphoric acid contains 3% of phosphorus, and the solid content of the precipitation slurry is 7wt%;
(2) Carrying out filter pressing washing on the precipitation slurry to obtain clear liquid 1;
(3) Mixing the clear solution 1 and the clear solution 2 to obtain a mixed clear solution, wherein the content of phosphorus element in the mixed clear solution is 0.1wt%, adding ferrous sulfate and hydrogen peroxide into the mixed clear solution, and the molar ratio of the phosphorus in the mixed clear solution to the ferrous sulfate and the hydrogen peroxide is 1:1.2:0.75 to obtain slurry A; slurry A has a solids content of 10%;
(4) The volume ratio of the precipitated slurry to the slurry A is 100:15, mixing to obtain mixed slurry B;
(5) The mixed slurry B is subjected to filter pressing and washing to obtain a washing filter cake;
(6) Adding water into a filter cake to prepare slurry C with the concentration of 15wt% and slurry D with the concentration of 5wt%;
(7) Adding 3wt% of 85% phosphoric acid into the slurry C at 55 ℃ to perform a first aging reaction, wherein the first aging reaction time is 1h, so as to obtain slurry E; adding 0.3wt% of 85% phosphoric acid into the slurry D for second aging, wherein the second aging reaction time is 1h, so as to obtain slurry F;
(8) After both the slurry E and the slurry F become white, the volume ratio of the slurry E to the slurry F is 0.3:1, mixing, preserving heat for 0.5h at 95 ℃, and then performing filter pressing washing to obtain clear liquid 2, and calcining a filter cake to obtain anhydrous ferric phosphate.
Comparative example 1
This comparative example differs from example 1 in that the filtrate wash water is not recycled, and slurry E and slurry F are not mixed, specifically comprising the steps of:
(1) Mixing 500mL of ferrous sulfate, phosphoric acid and hydrogen peroxide, and performing precipitation reaction to obtain a precipitation slurry, wherein the molar ratio of the ferrous sulfate to the phosphoric acid to the hydrogen peroxide is 1:1:0.75; the ferrous sulfate contains 60g/L of ferrous sulfide, the phosphoric acid contains 3% of phosphorus, and the solid content of the precipitation slurry is 8wt%;
(2) Carrying out filter pressing washing on the precipitation slurry to obtain a washing filter cake;
(3) Adding water into a filter cake to prepare slurry C with the concentration of 18wt% and slurry D with the concentration of 8wt%;
(4) Adding 4wt% of 85% phosphoric acid into the slurry C at 60 ℃ to perform a first aging reaction, wherein the first aging reaction time is 2 hours, so as to obtain slurry E; adding 0.2wt% of 85% phosphoric acid into the slurry D for a second aging reaction, wherein the second aging reaction time is 30min, so as to obtain slurry F;
(5) And respectively carrying out heat preservation reaction after both the slurry E and the slurry F turn white, carrying out filter pressing washing after heat preservation for 1h at 90 ℃, and mixing after respectively calcining filter cakes to obtain the anhydrous ferric phosphate.
Comparative example 2
This comparative example differs from example 1 only in that in step (7), a second aging reaction was performed by adding 4wt% phosphoric acid having a concentration of 85% to slurry D.
Comparative example 3
The preparation method of the lithium iron phosphate precursor provided by the comparative example comprises the following steps:
(1) Step (1) is the same as in example 1;
(2) Carrying out filter pressing washing on the precipitation slurry to obtain a washing filter cake;
(3) Step (6) is the same as in example 1;
(4) Step (7) is the same as in example 1;
(5) Step (8) was performed as in example 1.
Comparative example 4
The preparation method of the lithium iron phosphate precursor provided by the comparative example comprises the following steps:
(1) (5) the same as in example 1;
(6) Adding water into the first-washing filter cake to prepare slurry C with the concentration of 18 wt%;
(7) Adding 4wt% of 85% phosphoric acid into the slurry C at 60 ℃ to perform a first aging reaction, wherein the first aging reaction time is 30min, so as to obtain slurry E;
(8) And (3) preserving the temperature of the slurry E for 1h at 90 ℃ after whitening, and performing filter pressing washing to obtain clear liquid 2, and calcining a filter cake to obtain the anhydrous ferric phosphate.
Experimental example
Lithium iron phosphate precursors prepared in each of the examples and comparative examples were prepared as lithium iron phosphate using the following method: phosphorus in the prepared ferric phosphate and lithium in lithium carbonate are mixed according to the proportion of 1:1.005 molar ratio, adding 7wt% of white granulated sugar and 3wt% of PEG6000, sanding to 0.42 μm, and sintering at 770 ℃ for 9 h. The compacted density of lithium iron phosphate was measured and tested using an FT-100F powder automatic compaction densitometer, the results of which are shown in table 1.
TABLE 1
| Density of compaction | |
| Example 1 | 2.55g/cm 3 |
| Example 2 | 2.51g/cm 3 |
| Example 3 | 2.46g/cm 3 |
| Comparative example 1 | 2.15g/cm 3 |
| Comparative example 2 | 2.21g/cm 3 |
| Comparative example 3 | 2.28g/cm 3 |
| Comparative example 4 | 2.08g/cm 3 |
As can be seen by comparing fig. 2 with fig. 3: in the case of the precipitation section, when the filtrate and the washing water are not recycled in the precipitation section in comparative example 1, the particle size is relatively uniform, but in example 1, the amorphous iron phosphate with different particle sizes is obtained by the existence of particles with different sizes;
in terms of the aging section, the addition amount of phosphoric acid in the slurry E in the comparative example 1 is large, when the concentration of the slurry is high, the pH is low, the conversion of the crystal form is accelerated, the supersaturation degree is high, and the crystal nucleation is preferential to the crystal growth, so that the particles are fine; the addition amount of phosphoric acid in the slurry F is small, and when the concentration of the slurry is low, the particles are larger; however, in example 1, the size particles still exist after aging, i.e., the process is prone to forming iron phosphate with size particles;
by using the ferric phosphate, the lithium iron phosphate is prepared by adopting the same process, the particle size is uniform in comparative example 1, the powder compaction is small, and the particle size is 2.15g/cm 3 Whereas the size particles in example 1 were distinct, the powder compaction was high, 2.55g/cm 3 。
While the invention has been illustrated and described with reference to specific embodiments, it is to be understood that the above embodiments are merely illustrative of the technical aspects of the invention and not restrictive thereof; those of ordinary skill in the art will appreciate that: modifications may be made to the technical solutions described in the foregoing embodiments, or equivalents may be substituted for some or all of the technical features thereof, without departing from the spirit and scope of the present invention; such modifications and substitutions do not depart from the spirit of the corresponding technical solutions; it is therefore intended to cover in the appended claims all such alternatives and modifications as fall within the scope of the invention.
Claims (10)
1. The preparation method of the lithium iron phosphate precursor is characterized by comprising the following steps of:
(a) Mixing an iron source, a phosphorus source and an oxidant, and then carrying out precipitation reaction to obtain precipitation slurry; performing first washing on the precipitation slurry to obtain a first clear liquid;
(b) Mixing the first clear liquid and the second clear liquid to obtain a mixed clear liquid; adding the oxidant and the iron source into the mixed clear liquid to obtain slurry A; mixing the precipitation slurry with the slurry A, and then performing second washing to obtain a washing filter cake;
(c) Adding water into the first filter cake to prepare slurry C with the concentration of 15-20wt% and slurry D with the concentration of 5-10wt%;
(d) Performing a first aging reaction on the slurry C, and adding phosphoric acid into the slurry C in the first aging reaction process to obtain slurry E; performing a second aging reaction on the slurry D, and adding phosphoric acid into the slurry D in the second aging reaction process to obtain slurry F;
the content of phosphoric acid in the slurry E is 3-5 wt%;
the content of phosphoric acid in the slurry F is 0.1-0.3 wt%;
(e) Mixing the slurry E and the slurry F, and then performing mild reaction and second washing to obtain the second clear liquid and a second-stage filter cake; and calcining the secondary filter cake to obtain the lithium iron phosphate precursor.
2. The method for preparing a lithium iron phosphate precursor according to claim 1, wherein the content of phosphorus element in the mixed clear solution is 0.1wt% to 0.5wt%.
3. The method of preparing a lithium iron phosphate precursor according to claim 1, wherein the one filter cake comprises: first particles having a particle diameter of 200 to 500nm and second particles having a particle diameter of 10 to 50 nm.
4. The method of preparing a lithium iron phosphate precursor according to claim 1, wherein in step (a), the iron source, the phosphorus source and the oxidizing agent are in a molar ratio of (1 to 1.3): 1: (0.5-1) mixing;
preferably, in the step (b), the iron source, the phosphorus in the mixed clear solution and the oxidant are mixed according to a molar ratio of (1-1.3): 1: (0.5-1) adding;
preferably, in step (b), the precipitated slurry and the slurry a are mixed according to a volume ratio of 100: (5-15) mixing;
preferably, in the step (E), the mixing volume ratio of the slurry E to the slurry F is (0.1 to 0.3): 1.
5. the method of preparing a lithium iron phosphate precursor according to claim 1, wherein the solid content of the precipitation slurry is 7wt% to 10wt%;
preferably, the solid content of the slurry A is 7-10wt%.
6. The method for preparing a lithium iron phosphate precursor according to claim 1, wherein the temperature of the first aging reaction is 30-70 ℃;
preferably, the time of the first aging reaction is 30-120 min.
7. The method for preparing a lithium iron phosphate precursor according to claim 1, wherein the temperature of the second aging reaction is 30-70 ℃;
preferably, the second aging reaction takes 30 to 120 minutes.
8. The method for preparing a lithium iron phosphate precursor according to claim 1, wherein the temperature of the heat preservation is 85-95 ℃;
preferably, the time of the heat preservation is 0.5-4 h.
9. A lithium iron phosphate positive electrode material, characterized in that it is mainly prepared from a lithium iron phosphate precursor prepared by the preparation method of the lithium iron phosphate precursor according to any one of claims 1 to 8.
10. A lithium ion battery comprising the lithium iron phosphate positive electrode material of claim 9.
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| CN202311640257.9A CN117735502B (en) | 2023-12-01 | 2023-12-01 | Preparation method and application of lithium iron phosphate precursor |
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