Iron phosphate suitable for preparing long-circulation lithium iron phosphate and preparation method and application thereof

Abstract

The application provides iron phosphate suitable for preparing long-cycle lithium iron phosphate and a preparation method and application thereof. The XRD spectrum of the iron phosphate conforms to a PDF#29-0715 card and meets the following conditions: 4A8, 0B2, 1000C1500, 80D100, 0.975E0.995; wherein, A=I(102) / I(100), B=I(100) / I(104); C is the grain size of the (102) crystal face of the iron phosphate in the XRD spectrum, in the unit of D is the crystallinity of the iron phosphate, in the unit of %; and E is the molar ratio of iron elements and phosphorus elements in the iron phosphate. The iron phosphate provided by the application has suitable particle size and relatively stable crystal structure by limiting the sizes of different crystal faces of the iron phosphate and the peak intensity ratio, is used for preparing lithium iron phosphate, and can obtain more excellent long-cycle performance.

Claims

1. An iron phosphate suitable for preparing long-cycle lithium iron phosphate, characterized in that, The XRD pattern of the iron phosphate conforms to PDF#29-0715 card and meets the following conditions: 4<A≦8, 0<B<2, 1000≦C≦1500, 80<D<100, 0.975≦E≦0.995; in, A = I(102) / I(100), where I(102) is the XRD diffraction peak intensity of the iron phosphate (102) crystal plane in the XRD spectrum, and I(100) is the XRD diffraction peak intensity of the iron phosphate (100) crystal plane in the XRD spectrum. B = I(100) / I(104), where I(100) is the XRD diffraction peak intensity of the iron phosphate (100) crystal plane in the XRD spectrum, and I(104) is the XRD diffraction peak intensity of the iron phosphate (104) crystal plane in the XRD spectrum. C represents the grain size of the iron phosphate (102) crystal plane shown in the XRD pattern, in units of... D represents the crystallinity of the iron phosphate, expressed in %; E represents the molar ratio of iron to phosphorus in the iron phosphate.

2. The iron phosphate suitable for preparing long-cycle lithium iron phosphate according to claim 1, characterized in that, The condition A satisfies: 4 < A ≦ 6; And / or, the B satisfies: 1 ≦ B < 2.

3. A method for preparing iron phosphate suitable for preparing long-cycle lithium iron phosphate, characterized in that, include: The first phosphorus source solution, oxidant, and pH adjuster are mixed to obtain a mixed solution; Under stirring conditions, ferrous sulfate solution and the mixture are simultaneously added dropwise to opposite sides of a reaction vessel containing pure water to carry out the reaction. Then, the mixture undergoes a first filtration, a first washing, and pulping to obtain a first slurry. A second phosphorus source is added to the first slurry, and then the first slurry is aged at a first temperature until the first slurry turns white to obtain the second slurry. Iron solution is added to the second slurry, and a second aging process is carried out at a second temperature, followed by a second filtration, a second washing, and drying to obtain ferric phosphate dihydrate; the second temperature is higher than the first temperature. The ferric phosphate dihydrate is sintered to obtain the ferric phosphate.

4. The preparation method according to claim 3, characterized in that, The volume of the pure water is a L, and the total volume of the ferrous sulfate solution and the mixture is b L. The volume of a and the volume of b satisfy the following condition: 20% ≤ a / b ≤ 60%.

5. The preparation method according to claim 3, characterized in that, The molar amount of iron in the iron solution is 0.5-1% of the molar amount of iron in the product after the reaction; And / or, the iron solution includes at least one of ferrous sulfate solution, ferrous sulfate solution, ferric hydroxide solution, and ferrous oxalate solution.

6. The preparation method according to claim 3, characterized in that, The molar concentration of iron in the ferrous sulfate solution is equal to the molar concentration of phosphorus in the mixture; And / or, the ratio of the dropping rates of the ferrous sulfate solution and the mixture is (1.05-1.25):1; And / or, the reaction includes: Under stirring conditions, ferrous sulfate solution and the mixture are simultaneously added dropwise to opposite sides of the reaction vessel containing pure water until a yellow precipitate is formed and both the ferrous sulfate solution and the mixture have been added. Continue stirring for 15-30 minutes. And / or, the pH of the product after the reaction is 2.5-4.

5.

7. The preparation method according to claim 3, characterized in that, The molar amount of the second phosphorus source added is 10-25% of the molar amount of iron in the product after the reaction; And / or, the first temperature is 65-75°C; And / or, the second temperature is 88-95°C; And / or, the second aging time is 2-4 hours.

8. The preparation method according to claim 3, characterized in that, The molar ratio of phosphorus element in the first phosphorus source solution to the oxidant is 1:0.65-0.85, and the pH of the mixture is 3.5-4.5; And / or, the oxidant is at least one of hydrogen peroxide and ozone; And / or, the phosphorus source of the first phosphorus source solution and the second phosphorus source both include at least one of phosphoric acid, monoammonium phosphate, and diammonium phosphate; And / or, the pH adjuster includes at least one of ammonium bicarbonate, ammonia, and NaOH.

9. The preparation method according to claim 3, characterized in that, The ferrous sulfate solution is a refined ferrous sulfate solution produced as a byproduct of titanium dioxide production. And / or, the sintering is carried out in a protective gas atmosphere, the protective gas including at least one of air and inert gas; And / or, the sintering temperature is 500-650℃, and the sintering time is 2.5-5h.

10. A positive electrode active material, characterized in that, Includes lithium iron phosphate, wherein the lithium iron phosphate is prepared using the method of iron phosphate as described in claim 1 or 2 or the method of preparation as described in any one of claims 3 to 9.

11. A positive electrode plate, characterized in that, Includes the positive electrode active material as described in claim 10.

12. A secondary battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that, The positive electrode is the positive electrode as described in claim 11.

13. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 12.

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