A method for producing an active substance precursor

Abstract

The application relates to the technical field of lithium battery positive electrode material precursor preparation, in particular to a preparation method of an active material precursor, wherein during preparation, a metal salt aqueous solution A obtained by mixing FeSO4 and MnSO4 with different molar ratios, a metal salt aqueous solution B, an ammonia solution, a phosphoric acid or phosphate solution and a sodium hydroxide solution are prepared; then the metal salt aqueous solution A and the mixed solution are added into a co-precipitation reactor to generate a precursor crystal seed rich in Mn metal; the metal salt aqueous solution A and the metal salt aqueous solution B are mixed and added into the co-precipitation reactor to form a crystal with a shell-core structure with a concentration gradient; finally, a carbon source is added, and after washing and drying, the active material precursor with a carbon-coated shell-core structure with a concentration gradient is formed. The active material precursor is prepared by adopting a liquid-phase co-precipitation method, the active material precursor can be endowed with a concentration gradient, the cycle performance is better, the process is simple, the washing times are few, and resource waste is reduced.

Description

Technical Field

[0001] This invention relates to the field of lithium battery cathode material precursor preparation technology, and particularly to a method for preparing an active material precursor. Background Technology

[0002] In the field of lithium batteries, the prepared LiFe x Mn y During battery cycling, PO4 is easily dissolved due to the Jameur-Taylor effect, resulting in low cycle efficiency. Several existing technologies utilize hydrothermal methods to prepare core-shell LiFe with concentration gradients. x Mn y PO4 improves its recycling efficiency, but the hydrothermal method uses excessive Li, requiring high resource recovery standards. Furthermore, to provide lithium manganese iron phosphate active materials with a concentration gradient structure, multiple hydrothermal reactions and sintering processes are required. However, multiple hydrothermal methods necessitate multiple sample washing, drying, and heating reaction steps; this generates large amounts of wastewater containing transition metal resources and consumes significant energy, posing substantial challenges in resource utilization, environmental protection, and energy consumption. Therefore, this invention develops an active material, its precursor, and a method for preparing the precursor to address the problems existing in the prior art. Summary of the Invention

[0003] The purpose of this invention is to provide an active substance and its precursor, as well as a method for preparing the precursor, in order to solve the problems of complex and resource-wasting processing methods in the prior art.

[0004] The technical solution of this invention is: an active substance precursor, comprising a central part, an intermediate part, and an outer part, with an average chemical formula of: Fe x Mn y M z PO4 or Fe x Mn y M z A w PO4;

[0005] Where M is a hydrogen ion, a volatile cation, or a mixture thereof, and its average valence is a;

[0006] A is one or more doped ions with an average valence of b;

[0007] And it satisfies: 2x + 2y + az + bw = 3;

[0008] Fe and Mn elements have a continuous concentration gradient from the center to the outer surface.

[0009] Preferably, in the active substance precursor, the average molar ratio x:y of Fe to Mn is 4:6 to 1:9;

[0010] The Fe element has a concentration gradient that gradually increases from the center to the outer surface;

[0011] The Mn element has a concentration gradient that gradually decreases from the center to the outer surface.

[0012] The preparation method of the above-mentioned active substance precursor includes:

[0013] Prepare an aqueous solution A of a metal salt that forms the central part, including an iron salt solution and a manganese salt solution, with a molar ratio of x1 / y1;

[0014] Prepare an aqueous solution B of a metal salt that forms the outer surface, comprising an iron salt solution and a manganese salt solution, with a molar ratio of x2 / y2; wherein x1 / y1 < x2 / y2;

[0015] Prepare a mixed solution, including an aqueous ammonia solution, a phosphoric acid solution or a phosphate solution, and an alkaline solution;

[0016] A portion of the metal salt aqueous solution A and the mixed solution are added to a coprecipitation reactor forming an inert gas atmosphere to generate seed crystals containing Fe and Mn in a molar ratio of x1 / y1;

[0017] While the metal salt aqueous solution B is gradually added to the remaining metal salt aqueous solution A, the resulting B+A mixed solution is gradually and simultaneously added to the co-precipitation reactor containing Fe and Mn seeds to form a core-shell structure with a concentration gradient.

[0018] A carbon source is added to the coprecipitation reactor, and the precursor formed by the reaction is separated, washed with water and dried to form a carbon-coated core-shell structure active substance precursor with a concentration gradient.

[0019] Preferably, when the metal salt aqueous solution A and the metal salt aqueous solution B are mixed and added to the coprecipitation reactor, the mixed solution is continuously added to the coprecipitation reactor.

[0020] Preferably, when the mixed solution is mixed with the metal salt aqueous solution A, and when mixed with a combination of the metal salt aqueous solution A and the metal salt aqueous solution B, the addition rate of the ammonia aqueous solution is 1–800 mmol / h / L, the addition rate of the alkaline solution is 1–800 mmol / h / L, and the addition rate of the phosphoric acid solution or phosphate solution is 1–800 mmol / h / L, relative to the amount of solute added per liter of bottom liquid.

[0021] Preferably, the ammonia solution is added at a rate of 1–100 mmol / h / L, the alkaline solution is added at a rate of 1–100 mmol / h / L, and the phosphoric acid or phosphate solution is added at a rate of 1–100 mmol / h / L.

[0022] Furthermore, the addition rates of the phosphoric acid or phosphate solution, ammonia solution, and alkaline solution decrease sequentially to control the concentration of each solution.

[0023] Preferably, the aqueous solution of the metal salt A reacts with the mixed solution at a temperature of 20–80°C for 30–40 min;

[0024] After the metal salt aqueous solution A and the metal salt aqueous solution B are mixed, the mixed solution is added simultaneously and reacted at a temperature of 20-80°C for at least 1-72 hours.

[0025] Preferably, the cation concentration in both the metal salt aqueous solution A and the metal salt aqueous solution B is 0.1–5 mol / L, the iron salt solution is FeSO4 solution, and the manganese salt solution is MnSO4 solution; more preferably, the cation concentration in both the metal salt aqueous solution A and the metal salt aqueous solution B is 1.4–1.6 mol / L.

[0026] In the aqueous solution A of the metal salt, the molar ratio of FeSO4 to MnSO4 is 2:8 to 0.5:9.5;

[0027] In the aqueous solution B of the metal salt, the molar ratio of FeSO4 to MnSO4 is 3:7 to 5:5.

[0028] Preferably, the carbon source is one or more of glucose, sucrose, citric acid, carbon nanotubes, graphene, graphene oxide, or acetylene black, and the carbon coating content in the active substance precursor with a core-shell structure formed by treatment is 0.5-8 wt%; more preferably, the carbon coating content is 1.25-1.36 wt%.

[0029] An active substance was obtained based on an active substance precursor, mainly by using Fe as the active substance precursor. x Mn y M z PO4 with lithium source and metal oxide A3O b The mixture is then sintered in an inert gas atmosphere to obtain the final product.

[0030] or,

[0031] Fe, the precursor of active material x Mn y M z A w PO4 is mixed with a lithium source and sintered in an inert gas atmosphere to obtain the product.

[0032] Compared with the prior art, the advantages of the present invention are:

[0033] This invention uses a liquid-phase co-precipitation method to prepare active material precursors. Compared with the traditional solid-phase method, it can make the final cathode material have uniform particle size and good consistency, and can impart a concentration gradient to the active material precursor, resulting in better cycle characteristics. Compared with the traditional hydrothermal method, the process is simple, consumes less Li element, requires fewer washing cycles, and reduces resource waste. Attached Figure Description

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0035] Figure 1 This is a flowchart of a method for preparing an active substance precursor according to the present invention. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to specific embodiments:

[0037] An active substance precursor, comprising a central portion, an intermediate portion, and an outer portion, has the average chemical formula: Fe x Mn y M z (Aw)PO4.

[0038] Where M is hydrogen ion (H+) + ) or volatile cations (such as NH4+) 4+ ), or any mixture thereof, with an average valence of a;

[0039] A is one or more doped ions, including B, mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, and W, with an average valence of b; the above doped ions can be added in the co-precipitation reaction or during the sintering process.

[0040] When dopant ions are added in the coprecipitation reaction, the average chemical formula of the obtained active material precursor is Fe. x Mn y M z AwPO4, and satisfies 2x+2y+az+bw=3;

[0041] When dopant ions are added during sintering without being added in the co-precipitation reaction, the average chemical formula of the obtained active material precursor is Fe. x Mn y M z PO4, and satisfies 2x + 2y + az = 3;

[0042] Fe and Mn elements have a continuous concentration gradient from the center to the outer surface; that is, Fe has a concentration gradient that gradually increases from the center to the outer surface, while Mn has a concentration gradient that gradually decreases from the center to the outer surface.

[0043] Regarding a method for preparing an active substance precursor, such as Figure 1 As shown, the main steps are as follows.

[0044] Example 1

[0045] (1) Prepare an aqueous solution A of metal salt that forms the center of the active substance precursor, including an iron salt solution and a manganese salt solution. The iron salt solution is FeSO4 solution and the manganese salt solution is MnSO4 solution, wherein the molar ratio of FeSO4 to MnSO4 is 0.5:9.5.

[0046] (2) Prepare an aqueous solution B of metal salts that forms the outer surface of the active substance precursor, including FeSO4 solution and MnSO4 solution, wherein the molar ratio of FeSO4 to MnSO4 is 3:7.

[0047] (3) Prepare a mixed solution, including 15 wt% ammonia solution, 10 wt% phosphoric acid solution, and 25 wt% alkaline solution; in this embodiment, the alkaline solution is NaOH solution;

[0048] (4) Prepare a coprecipitation reactor. Add 4L of distilled water to the coprecipitation reactor and introduce nitrogen gas at a rate of 2L / min to remove residual oxygen. Maintain the solution temperature at 50℃ and the stirring speed at 400rpm. Then add 10ml of the above NaOH solution and 200ml of the above ammonia water to form a bottom solution, so that the pH value of the bottom solution is maintained at 12.

[0049] (5) Add part of the metal salt aqueous solution A and the mixed solution to the coprecipitation reactor in which an inert gas atmosphere is formed to generate seed crystals containing Fe and Mn in a molar ratio of 0.5:9.5. When adding, the addition rate of metal salt aqueous solution A is 60 mmol / h / L, the addition rate of ammonia solution is 30 mmol / h / L, the addition rate of phosphoric acid solution is 90 mmol / h / L, and the addition rate of NaOH solution is 10 mmol / h / L, based on the amount of solute added per hour relative to the bottom liquid. The whole process lasts for 30 min.

[0050] (6) The metal salt aqueous solution B was mixed with the remaining metal salt aqueous solution A at a rate of 1.5 ml / h. The resulting B+A mixed solution was gradually and synchronously added to a coprecipitation reactor containing Fe and Mn seed crystals to form a core-shell structure with a concentration gradient. During this process, the mixed solution was continuously added to the coprecipitation reactor. The addition rates of the mixed metal salt aqueous solution A and metal salt aqueous solution B were 60 mmol / h / L, the addition rate of the ammonia solution was 30 mmol / h / L, the addition rate of the phosphoric acid solution was 90 mmol / h / L, and the addition rate of the NaOH solution was 10 mmol / h / L. The entire process lasted for 31.5 h.

[0051] (7) Add glucose to a coprecipitation reactor and separate the precursor formed by the reaction. After washing with water, dry at 120°C to form a carbon-coated core-shell structure active substance precursor with a concentration gradient, wherein the carbon coating content accounts for 1.3 wt%.

[0052] It should be noted that glucose is used as the carbon source in this embodiment. Of course, the carbon source can also be one or more of sucrose, citric acid, carbon nanotubes, graphene, graphene oxide or acetylene black.

[0053] The average molar ratio of Mn:Fe in the active substance precursor prepared by the above method is 9:1, and the corresponding average chemical formula of the active substance precursor is: Fe 0.1 Mn 0.9 NH4PO4.

[0054] After obtaining the active substance precursor, the active substance precursor Fe 0.1 Mn 0.9 NH4PO4 with lithium source LiOH and metal oxide A3O b In this embodiment, the metal oxide used is WO3, with W as the dopant ion. After mixing, the mixture is sintered at 700°C for 5 hours under a nitrogen atmosphere to form LiMn. 0.87 Fe 0.10 W 0.03 PO4 is an active substance.

[0055] The lithium-ion battery prepared using the active material of this embodiment as the positive electrode material has a tap density of 1.7 g / ml, a compaction density of 2.4 g / ml, a specific capacity of 149 mAh / g, and an initial coulombic efficiency of 92%; the capacity retention rate after 100 cycles is 98.7%.

[0056] Example 2

[0057] (1) Prepare a metal salt aqueous solution A, including FeSO4 solution and MnSO4 solution, wherein the molar ratio of FeSO4 to MnSO4 is 1:9;

[0058] (2) Prepare metal salt aqueous solution B, including FeSO4 solution and MnSO4 solution, with a molar ratio of FeSO4 to MnSO4 of 3:7;

[0059] (3) Prepare a mixed solution comprising 15 wt% ammonia solution, 10 wt% phosphoric acid solution, and 25 wt% NaOH solution;

[0060] (4) Prepare a coprecipitation reactor. Add 4L of distilled water to the coprecipitation reactor and introduce nitrogen gas at a rate of 2L / min to remove residual oxygen. Maintain the solution temperature at 50℃ and the stirring speed at 400rpm. Then add 10ml of the above NaOH solution and 200ml of the above ammonia water to keep the solution pH at 12.

[0061] (5) Add part of the metal salt aqueous solution A and the mixed solution to the coprecipitation reactor in which an inert gas atmosphere is formed to generate seed crystals containing Fe and Mn in a molar ratio of 1:9. When adding, the addition rate of metal salt aqueous solution A is 60 mmol / h / L, the addition rate of ammonia solution is 30 mmol / h / L, the addition rate of phosphoric acid solution is 90 mmol / h / L, and the addition rate of NaOH solution is 10 mmol / h / L, based on the amount of solute added per hour relative to the bottom liquid. The whole process lasts for 30 min.

[0062] (6) The metal salt aqueous solution B was mixed with the remaining metal salt aqueous solution A at a rate of 1.5 ml / h. The resulting B+A mixed solution was gradually and synchronously added to a coprecipitation reactor containing Fe and Mn seed crystals to form a core-shell structure with a concentration gradient. During this process, the mixed solution was continuously added to the coprecipitation reactor. The addition rates of the mixed metal salt aqueous solution A and metal salt aqueous solution B were 60 mmol / h / L, the addition rate of the ammonia solution was 30 mmol / h / L, the addition rate of the phosphoric acid solution was 90 mmol / h / L, and the addition rate of the NaOH solution was 10 mmol / h / L. The entire process lasted for 31.5 h.

[0063] (7) Add glucose to a coprecipitation reactor and separate the precursor formed by the reaction. After washing with water, dry at 120°C to form a carbon-coated core-shell structure active substance precursor with a concentration gradient, wherein the carbon coating content accounts for 1.3 wt%.

[0064] The difference between Example 2 and Example 1 is that the molar ratio of FeSO4 to MnSO4 in the prepared metal salt aqueous solution A is different; in the active material precursor prepared by the above method, the average molar ratio of Mn:Fe is 8:1, and the average chemical formula of the corresponding active material precursor is: Fe 1 / 9 Mn 8 / 9 NH4PO4.

[0065] After obtaining the active substance precursor, the active substance precursor Fe 1 / 9 Mn 8 / 9 NH4PO4 is mixed with lithium source LiOH and WO3, with W as a dopant ion, and then sintered at 700℃ for 5 hours under a nitrogen atmosphere to form LiMn. 0.86 Fe 0.11 W 0.03 PO4 is an active substance.

[0066] The lithium-ion battery prepared using the active material of this embodiment as the positive electrode material has a tap density of 1.7 g / ml, a compaction density of 2.4 g / ml, a specific capacity of 146 mAh / g, and an initial coulombic efficiency of 90%; the capacity retention rate after 100 cycles is 99.2%.

[0067] Comparative Example 1

[0068] The difference between this comparative example and Example 1 or Example 2 is that:

[0069] Prepare an aqueous solution of a metal salt, A, comprising FeSO4 solution and MnSO4 solution, wherein the molar ratio of FeSO4 to MnSO4 is 1:9;

[0070] Prepare an aqueous solution of a metal salt, B, including FeSO4 solution and MnSO4 solution, with the molar ratio of FeSO4 to MnSO4 being 1:9.

[0071] In the prepared active substance precursor, the average molar ratio of Mn:Fe was 9:1, and the corresponding average chemical formula of the active substance precursor was: Fe 0.1 Mn 0.9 NH4PO4.

[0072] After obtaining the active substance precursor, the active substance precursor Fe 0.1 Mn 0.9 NH4PO4 is mixed with lithium source LiOH and WO3, with W as a dopant ion, and then sintered at 700℃ for 5 hours under a nitrogen atmosphere to form LiMn. 0.87 Fe 0.10 W 0.03 PO4 is an active substance.

[0073] Using the active material prepared in this comparative example as the positive electrode material, the prepared lithium-ion battery has a tap density of 1.6 g / ml, a compaction density of 2.3 g / ml, a specific capacity of 149 mAh / g, an initial coulombic efficiency of 89%, and a capacity retention rate of 81.3% after 100 cycles.

[0074] Comparing Comparative Example 1 with Examples 1 and 2, when there is no concentration gradient between Fe and Mn elements during the preparation of the active material precursor, the capacity retention rate of the lithium battery decreases significantly.

[0075] Comparative Example 2

[0076] The difference between this comparative example and Example 1 or Example 2 is that:

[0077] Prepare an aqueous solution of a metal salt, A, comprising FeSO4 solution and MnSO4 solution, wherein the molar ratio of FeSO4 to MnSO4 is 1:8;

[0078] Prepare an aqueous solution of a metal salt, B, including FeSO4 solution and MnSO4 solution, with the molar ratio of FeSO4 to MnSO4 being 1:8.

[0079] In the active substance precursor prepared by the above method, the average molar ratio of Mn:Fe is 8:1, and the corresponding average chemical formula of the active substance precursor is: Fe 1 / 9 Mn 8 / 9 NH4PO4.

[0080] After obtaining the active substance precursor, the active substance precursor Fe 1 / 9 Mn 8 / 9 NH4PO4 is mixed with lithium source LiOH and WO3, with W as a dopant ion, and then sintered at 700℃ for 5 hours under a nitrogen atmosphere to form LiMn with an average chemical formula of 0.5%. 0.86 Fe 0.11 W 0.03 PO4 is an active substance.

[0081] Using the active material prepared in this comparative example as the positive electrode material, the prepared lithium-ion battery has a tap density of 1.6 g / ml, a compaction density of 2.3 g / ml, a specific capacity of 146 mAh / g, an initial coulombic efficiency of 88%, and a capacity retention rate of 84.2% after 100 cycles.

[0082] In Comparative Example 2, by adjusting the Mn:Fe ratio, the final battery performance was not significantly different from that in Comparative Example 1, which further proves that when there is no concentration gradient between Fe and Mn elements in the active material precursor, the capacity retention rate of the lithium battery will decrease significantly.

[0083] The above embodiments are merely illustrative of the technical concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of the present invention is defined by the appended claims rather than the foregoing description, and thus all changes falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention.

Claims

1. A method for preparing an active substance precursor, comprising: Prepare aqueous solutions of metal salts A and B, wherein both aqueous solutions of metal salts A and B contain iron salts and manganese salts, and the Fe / Mn molar ratio in aqueous solution of metal salts A is less than the Fe / Mn molar ratio in aqueous solution of metal salts B; Prepare a mixed solution C, comprising an aqueous ammonia solution, a phosphoric acid solution or a phosphate solution, and a sodium hydroxide solution; Distilled water is added to the coprecipitation reactor as the base liquid, and inert gas is introduced at a rate of 2L / min to remove residual oxygen; part of the metal salt aqueous solution A and the mixed solution C are added to the coprecipitation reactor to form an inert gas atmosphere, and reacted at a temperature of 20-80°C for 30-40 min to generate seed crystals containing Fe / Mn molar ratio of x1 / y1. While the metal salt aqueous solution B is gradually added to the remaining metal salt aqueous solution A, the resulting B+A mixed solution D is gradually and simultaneously added to the co-precipitation reactor containing Fe and Mn seeds. The reaction is carried out at a temperature of 20-80°C for 1-72 hours to form a core-shell structure with a concentration gradient. A carbon source is added to the co-precipitation reactor, and the precursor formed by the reaction is separated, washed with water and dried to form a carbon-coated shell-core structure active substance precursor with a concentration gradient, wherein the carbon coating content accounts for 0.5 to 8 wt% of the active substance precursor. In this process, the mixed solution C is added to the co-precipitation reactor. Relative to the bottom liquid in the co-precipitation reactor, the addition rate of the ammonia solution is 1–800 mmol / h / L, the addition rate of the sodium hydroxide solution is 1–800 mmol / h / L, and the addition rate of the phosphoric acid or phosphate solution is 1–800 mmol / h / L; and the addition rates of the phosphoric acid or phosphate solution, ammonia solution, and sodium hydroxide solution decrease sequentially. In both the metal salt aqueous solution A and the metal salt aqueous solution B, the cation concentration is 0.1–5 mol / L; the molar ratio of FeSO4 to MnSO4 in the metal salt aqueous solution A is 2:8–0.5:9.5; and the molar ratio of FeSO4 to MnSO4 in the metal salt aqueous solution B is 3:7–5:

5. The iron salt is prepared using FeSO4 solution, and the manganese salt is prepared using MnSO4 solution; the phosphate is selected from at least one of ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, sodium phosphate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, or potassium phosphate; the carbon source is selected from one or more of glucose, sucrose, citric acid, carbon nanotubes, graphene, graphene oxide, or acetylene black. The addition of the mixed solution C is carried out throughout the entire reaction process.

2. The method for preparing an active substance precursor according to claim 1, characterized in that: In the active substance precursor, the average molar ratio x:y of Fe to Mn is 2:3 to 1:9; The Fe element has a concentration gradient that gradually increases from the center to the outer surface; The Mn element has a concentration gradient that gradually decreases from the center to the outer surface.

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