Preparation method of positive electrode active material

Abstract

The invention relates to the technical field of lithium battery positive electrode material preparation, in particular to a lithium battery positive electrode active material and a preparation method thereof. The preparation method comprises the following steps: 1, preparing a metal salt water solution A, a metal salt water solution B, a water solution C containing a water-soluble doped metal compound, an ammonia water solution, a phosphoric acid or phosphate solution and an alkali solution, wherein the metal salt water solution A and the metal salt water solution B are obtained by mixing FeSO4 and MnSO4 in different molar ratios; 2, adding the metal salt aqueous solution A and the mixed solution into a coprecipitation reactor in which an inert gas atmosphere is formed, and meanwhile, generating a precursor seed crystal rich in Mn metal; the method comprises the following steps: mixing a metal salt aqueous solution A and a metal salt aqueous solution B, and adding the mixture into a coprecipitation reactor to form a core-shell structure crystal with concentration gradient; 3, adding a carbon source, washing and drying to form a carbon-coated active substance precursor with a concentration gradient shell-core structure; and 4, mixing the active substance precursor with a lithium source and the ternary positive electrode material, and performing high-temperature sintering in an inert gas atmosphere to obtain the composite positive electrode material. The active substance precursor is prepared by adopting a liquid-phase coprecipitation method, so that the active substance precursor can be endowed with a concentration gradient, and the cycle characteristic of the active substance can be better; the precursor is directly compounded with the ternary positive electrode material, so that the process can be simplified, the cleaning times and the resource waste are reduced, and the stability and the energy density of the positive electrode material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of cathode materials for lithium batteries, and particularly relates to a method for preparing a cathode active material. Background Art

[0002] In the field of lithium batteries, the prepared LiFe x Mn y PO 4 During the battery cycling process, due to the Jahn-Teller effect of the Mn element, it is relatively easy to dissolve, resulting in a low cycling efficiency. In the prior art, several methods for preparing a core-shell structure with a concentration gradient by hydrothermal method for LiFe x Mn y PO 4 have improved its cycling efficiency. However, an excessive amount of Li element is used in the hydrothermal method, which requires a high recycling requirement for resources. In addition, to provide a lithium iron phosphate manganese active material with a concentration gradient structure, a method of multiple hydrothermal reactions and multiple sinterings is required. However, the multiple hydrothermal method requires multiple rinsing of samples, multiple drying, and multiple heating reaction steps; it generates a large amount of wastewater containing transition metal resources in engineering and consumes a large amount of energy, presenting major problems in terms of resource utilization, environmental protection, and energy consumption. On the other hand, mixing lithium iron phosphate manganese with a ternary cathode material can improve the capacity and cycling stability of the cathode active material. However, the traditional method requires sintering the lithium iron phosphate manganese first and then sintering it with the ternary cathode material to form a composite active material; such a method undergoes multiple sinterings and has a high energy consumption during the production process. Therefore, the present invention has developed a method for preparing a cathode active material for a lithium battery to solve the problems existing in the prior art. Summary of the Invention

[0003] The object of the present invention is to provide a method for preparing an active material to solve the problems and technical issues of complex processing methods and resource waste in the prior art.

[0004] The technical solution of the present invention is: An active material includes lithium iron phosphate manganese (LiFe x Mn y PO 4 ) and a ternary cathode material (LiNi a Mn b Co c O 3 ),

[0005] wherein the lithium iron phosphate manganese includes a central part, an intermediate part, and an outer part, and its average chemical formula is: LiFe x Mn y PO 4 ,

[0006] and satisfy: 2x + 2y = 3;

[0007] Preferably, in the active material precursor, the average molar ratio x:y of Fe to Mn is 2:8 to 1:9;

[0008] The Fe element has a concentration gradient that gradually increases from the central part to the outer surface part;

[0009] The Mn element has a concentration gradient that gradually decreases from the central part to the outer surface part;

[0010] Based on the above method for preparing an active material, it includes:

[0011] Prepare a metal salt aqueous solution A for forming the central part, including an iron salt solution and a manganese salt solution, and the molar ratio is x1 / y1;

[0012] Prepare a metal salt aqueous solution B for forming the outer surface part, including an iron salt solution and a manganese salt solution, and the molar ratio is x2 / y2; wherein, x1 / y1 < x2 / y2;

[0013] Prepare a mixed solution, including an ammonia water solution, a phosphoric acid solution or a phosphate solution, and an alkali solution;

[0014] Add the metal salt aqueous solution A and the mixed solution into a co-precipitation reactor formed with an inert gas atmosphere to generate seeds with an Fe, Mn molar ratio of x1 / y1;

[0015] Mix the metal salt aqueous solution A and the metal salt aqueous solution B to form an aqueous solution with a decreasing Mn element concentration over time, and add it to the co-precipitation reactor to form a core-shell structure with a concentration gradient, and the shell layer contains crystals with a Ti concentration of a2;

[0016] Add a carbon source into the co-precipitation reactor, and separate the precursor formed by the reaction, and after washing and drying, form an active material precursor with a carbon-coated and core-shell structure with a concentration gradient.

[0017] Preferably, when mixing the metal salt aqueous solution A and the metal salt aqueous solution B and adding them into the co-precipitation reactor, continuously add the mixed solution into the co-precipitation reactor.

[0018] Preferably, when mixing the mixed solution with the metal salt aqueous solution A, and when mixing with the combination of the metal salt aqueous solution A and the metal salt aqueous solution B, the feeding rate of the ammonia water solution is 1 to 800 mmol / h / L, the feeding rate of the alkali solution is 1 to 800 mmol / h / L, and the feeding rate of the phosphoric acid solution or the phosphate solution is 1 to 800 mmol / h / L.

[0019] Preferably, the feeding rate of the ammonia water solution is 1-100 mmol / h / L, the feeding rate of the alkali solution is 1-100 mmol / h / L, and the feeding rate of the phosphoric acid or phosphate solution is 1-100 mmol / h / L;

[0020] Moreover, the feeding rates of the phosphoric acid or phosphate solution, ammonia water solution, and alkali solution decrease in sequence to control the concentrations of the solutions.

[0021] Preferably, the metal salt aqueous solution A reacts with the mixed solution at a temperature of 30-80 °C for 30-40 min;

[0022] After the metal salt aqueous solution A is mixed with the metal salt aqueous solution B, the mixed solution is added synchronously and reacts at a temperature of 30-80 °C for at least 20-60 h.

[0023] Preferably, in the metal salt aqueous solution A and the metal salt aqueous solution B, the cation concentration is 0.1-5 mol / L, the iron salt solution uses FeSO 4 solution, and the manganese salt solution uses MnSO 4 solution; more preferably, the cation concentration in the metal salt aqueous solution A and the metal salt aqueous solution B is 1.4-1.6 mol / L;

[0024] In the metal salt aqueous solution A, the molar ratio of FeSO 4 to MnSO 4 is 2:8-0.5:9.5;

[0025] In the metal salt aqueous solution B, the molar ratio of FeSO 4 to MnSO 4 is 3:7-5:5.

[0026] Preferably, the carbon source uses glucose, and the carbon coating content in the active material precursor with a carbon-coated and concentration-gradient core-shell structure formed after treatment accounts for 0.5-3 wt%; more preferably, the carbon coating content accounts for 1.25-1.36 wt%.

[0027] Based on an active material precursor, an active material is obtained. Mainly, the active material precursor is mixed with a lithium source and a ternary cathode material and then sintered at high temperature in an inert gas atmosphere to obtain a composite cathode active material.

[0028] Compared with the prior art, the advantages of the present invention are:

[0029] The present invention prepares the active material precursor by the liquid-phase coprecipitation method. Compared with the traditional solid-phase method, it can make the particle size of the finally prepared cathode material uniform and have good consistency, and can endow the active material precursor with a concentration gradient and better cycling performance. Compared with the traditional solid-phase method for doping ternary cathode materials, it reduces the number of sintering times and saves energy. Compared with the traditional hydrothermal method, the process is simple, the amount of Li element consumed is less, the number of washing times is small, and resource waste is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be further described below in conjunction with the drawings and embodiments:

[0031] Figure 1 It is a flowchart of a method for preparing an active material precursor according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] The content of the present invention will be further described in detail below in conjunction with specific embodiments:

[0033] An active material includes lithium iron manganese phosphate (LiFe x Mn y PO 4 ) and a ternary cathode material (LiNi a Mn b Co c O 3 ), wherein the lithium iron manganese phosphate includes a central part, an intermediate part and an outer part, and its average chemical formula is: LiFe x Mn y PO 4 ,

[0034] and satisfies: 2x + 2y = 3;

[0035] Among them, the Fe and Mn elements have a continuous concentration gradient from the central part to the outer part. The Fe element has a concentration gradient that gradually increases from the central part to the outer part; the Mn element has a concentration gradient that gradually decreases from the central part to the outer part.

[0036] Regarding a method for preparing an active material, as Figure 1 shown, its main steps are as follows:

[0037] Example 1

[0038] (1) Prepare a metal salt aqueous solution A for forming the central part of the active material precursor, including an iron salt solution and a manganese salt solution. The iron salt solution uses FeSO 4 solution, and the manganese salt solution uses MnSO 4 solution, wherein the molar ratio of FeSO 4 to MnSO 4 is 0.5:9.5;

[0039] (2) Prepare an aqueous metal salt solution B for forming the outer surface of the active material precursor, including FeSO 4 solution, MnSO 4 solution, and the molar ratio of FeSO 4 to MnSO 4 is 3:7;

[0040] (3) Prepare a mixed solution, including an aqueous ammonia solution with a weight percentage of 15 wt%, a phosphoric acid solution with a weight percentage of 10 wt%, and an alkali solution with a weight percentage of 25 wt%; in this embodiment, the alkali solution is a NaOH solution;

[0041] (4) Prepare a co-precipitation reactor, add 4 L of distilled water to the co-precipitation reactor, and introduce nitrogen into it at a rate of 2 L / min to remove residual oxygen; maintain the solution temperature at 50 °C and the stirring speed at 400 rpm;

[0042] (5) Add the aqueous metal salt solution A, aqueous solution C, and the mixed solution to the co-precipitation reactor under an inert gas atmosphere to generate seeds with a Fe:Mn molar ratio of 0.5:9.5; when adding, the feeding rate of the aqueous metal salt solution A is 60 mmol / h / L, the feeding rate of the aqueous ammonia solution is 20 mmol / h / L, the feeding rate of the phosphoric acid solution is 90 mmol / h / L, and the feeding rate of the NaOH solution is 10 mmol / h / L, and the whole process lasts for 30 min;

[0043] (6) Mix the aqueous metal salt solution B with the aqueous metal salt solution A at a feeding rate of 1.5 mmol / h to form an aqueous solution with a decreasing Mn element concentration over time, and add it to the co-precipitation reactor to form a core-shell structured crystal with a concentration gradient; during this process, continuously add the mixed solution to the co-precipitation reactor while increasing the feeding rate of the aqueous solution C; among them, the feeding rate of the mixed aqueous metal salt solution A and aqueous metal salt solution B is 60 mmol / h / L, the feeding rate of the aqueous ammonia solution is 20 mmol / h / L, the feeding rate of the phosphoric acid solution is 90 mmol / h / L, and the feeding rate of the NaOH solution is 10 mmol / h / L, and the whole process lasts for 31.5 h;

[0044] (7) Add glucose to the co-precipitation reactor, separate the precursor formed by the reaction, wash it with water, and dry it at 120 °C to form an active material precursor with a core-shell structure coated with carbon and having a concentration gradient, where the carbon coating content accounts for 1.3 wt%.

[0045] Among the active material precursors prepared by the above method, the average molar ratio of Mn:Fe is 9:1, and the average chemical formula of the corresponding active material precursor is: Fe 0.1 Mn 0.9 NH 4 PO 4 。

[0046] After the active material precursor is prepared, the active material precursor Fe 0.1 Mn 0.9 NH 4 PO 4 is mixed with the lithium source LiOH and the ternary material LiNi 5 Mn 3 Co 2 O 3 in a molar ratio of 0.95:0.98:0.05. After mixing, it is sintered at 700 °C for 5 h in a nitrogen atmosphere to obtain an average chemical formula of the composite active material as:

[0047] (LiFe 0.1 Mn 0.9 PO 4 ) 0.95 (LiNi 0.5 Mn 0.3 Co 0.2 O 3 ) 0.05

[0048] Using the composite active material of this example as the cathode material, the prepared lithium-ion battery has a tap density of 1.94 g / ml, a compression density of 2.72 g / ml, a specific capacity of 157 mAh / g, and an initial Coulombic efficiency of 96%; the capacity retention rate that can be achieved after 100 cycles is 99.6%.

[0049] Example 2

[0050] (1) Prepare the metal salt aqueous solution A, including FeSO 4 solution and MnSO 4 solution, where the molar ratio of FeSO 4 to MnSO 4 is 1:9;

[0051] (2) Prepare the metal salt aqueous solution B, including FeSO 4 solution and MnSO 4 solution, and the molar ratio of FeSO 4 to MnSO 4 is 3:7;

[0052] (3) Prepare a mixed solution, including an ammonia water solution with a weight percentage of 15 wt%, a phosphoric acid solution with a weight percentage of 10 wt%, and a NaOH solution with a weight percentage of 25 wt%.

[0053] (4) Prepare a co-precipitation reactor, add 4 L of distilled water to the co-precipitation reactor, and introduce nitrogen into it at a rate of 2 L / min to remove residual oxygen; maintain the solution temperature at 50 °C and the stirring speed at 400 rpm; then add 10 ml of the above NaOH solution and 200 ml of the above ammonia water to keep the solution pH at 12.

[0054] (5) Add the metal salt aqueous solution A and the mixed solution to the co-precipitation reactor with an inert gas atmosphere to generate seeds with a molar ratio of Fe to Mn of 1:9; when adding, the feeding rate of the metal salt aqueous solution A is 60 mmol / h / L, the feeding rate of the ammonia water solution is 20 mmol / h / L, the feeding rate of the phosphoric acid solution is 90 mmol / h / L, and the feeding rate of the NaOH solution is 10 mmol / h / L, and the whole process lasts for 30 min.

[0055] (6) Mix the metal salt aqueous solution B with the metal salt aqueous solution A at a feeding rate of 1.5 mmol / h to form an aqueous solution with a decreasing concentration of Mn element over time, and add it to the co-precipitation reactor to form a crystalline core-shell structure with a concentration gradient; during this process, continuously add the mixed solution to the co-precipitation reactor; among them, the feeding rate of the mixed metal salt aqueous solution A and the metal salt aqueous solution B is 60 mmol / h / L, the feeding rate of the ammonia water solution is 20 mmol / h / L, the feeding rate of the phosphoric acid solution is 90 mmol / h / L, and the feeding rate of the NaOH solution is 10 mmol / h / L, and the whole process lasts for 31.5 h.

[0056] (7) Add glucose to the co-precipitation reactor, separate the formed precursor, wash it with water, and dry it at 120 °C to form an active material precursor with a carbon-coated and concentration-gradient core-shell structure, where the carbon coating content accounts for 1.3 wt%.

[0057] The difference between this Example 2 and Example 1 is that the molar ratio of FeSO 4 and MnSO 4 in the prepared metal salt aqueous solution A is different; in the active material precursor prepared based on 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 NH 4 PO 4 .

[0058] After the active material precursor is prepared, the active material precursor Fe 1 / 9 Mn 8 / 9 NH 4 PO 4 is mixed with the lithium source LiOH, the ternary material LiNi 5 Mn 3 Co 2 O 3 in a molar ratio of 0.95:0.98:0.05. After mixing, it is sintered at 700 °C for 5 h in a nitrogen atmosphere to obtain a composite active material with an average chemical formula of:

[0059] (LiFe 1 / 9 Mn 8 / 9 PO 4 ) 0.95 (LiNi 0.5 Mn 0.3 Co 0.2 O 3 ) 0.05

[0060] Using the active material of this example as the cathode material, the prepared lithium-ion battery has a tap density of 1.92 g / ml, a compaction density of 2.71 g / ml, a specific capacity of 154 mAh / g, and an initial Coulombic efficiency of 95.5%; the capacity retention rate that can be achieved after 100 cycles is 99.3%.

[0061] Comparative Example 1

[0062] In this comparative example, the difference from Example 1 or Example 2 is that:

[0063] Prepare an aqueous metal salt solution A, including FeSO 4 solution, MnSO 4 solution, where the molar ratio of FeSO 4 to MnSO 4 is 1:9;

[0064] Prepare an aqueous metal salt solution B, including FeSO 4 solution, MnSO 4 solution, and the molar ratio of FeSO 4 to MnSO 4 is also 1:9.

[0065] In the prepared active material precursor, the average molar ratio of Mn:Fe is 9:1, and the average chemical formula of the corresponding active material precursor is: Fe 0.1 Mn 0.9 NH 4 PO 4 .

[0066] After the active material precursor is prepared, the active material precursor Fe 0.1 Mn 0.9 NH 4 PO 4 is mixed with the lithium source LiOH, and the ternary material LiNi 5 Mn 3 Co 2 O 3 is obtained by sintering at 700 °C for 5 h in an atmosphere after mixing in a molar ratio of 0.95:0.98:0.05. The average chemical formula of the formed composite active material is:

[0067] (LiFe 0.1 Mn 0.9 PO 4 ) 0.95 (LiNi 0.5 Mn 0.3 Co 0.2 O 3 ) 0.05

[0068] Using the active material of this comparative example as the cathode material, the prepared lithium-ion battery has a tap density of 1.91 g / ml, a compression density of 2.38 g / ml, a specific capacity of 150 mAh / g, and an initial Coulomb efficiency of 88.7%; the capacity retention rate that can be achieved after 100 cycles is 85.3%.

[0069] Comparing this comparative example 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.

[0070] Comparative Example 2

[0071] In this comparative example, the difference from Example 1 or Example 2 is that:

[0072] Prepare an aqueous metal salt solution A, including FeSO 4 solution and MnSO 4 solution, where the molar ratio of FeSO 4 to MnSO 4 is 1:8;

[0073] Prepare an aqueous metal salt solution B, including FeSO 4 solution and MnSO 4 solution, and the molar ratio of FeSO 4 to MnSO 4 is also 1:8.

[0074] In the active material 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 material precursor is: Fe 0.1 Mn 0.9 NH 4 PO 4 .

[0075] After the active material precursor is prepared, the active material precursor Fe 0.1 Mn 0.9 NH 4 PO 4 It was mixed with lithium source LiOH at a molar ratio of 0.97:1 and sintered at 700℃ for 5h in a nitrogen atmosphere to form an average chemical formula of LiFe 0.1 Mn 0.9 PO 4 of living matter.

[0076] The lithium-ion battery prepared by using the active material of this embodiment as the positive electrode material has a tap density of 1.7g / ml, a compaction density of 2.5g / ml, a specific capacity of 149mAh / g, an initial coulombic efficiency of 92%; and a capacity retention rate of 98.1% that can be achieved after 100 cycles.

[0077] In this comparative example, when the lithium manganese iron phosphate active material is not compounded with the ternary active material, the capacity retention rate of the lithium battery will decrease significantly.

[0078] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the scope of protection of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is limited by the attached claims rather than the above description, and it is intended to include all changes within the meaning and scope of the equivalent elements of the claims in the present invention.

Claims

1. A positive electrode active material, characterized in that: Including lithium manganese iron phosphate (LiFe x Mn y PO4) and ternary cathode materials (LiNi a Mn b Co c O3), The lithium manganese iron phosphate includes a central part, a middle part and an outer part, and its average chemical formula is: Li Fe x Mn y PO4, And it satisfies: 2x+2y=3; Among them, Fe and Mn elements have a continuous concentration gradient from the center to the surface.

2. A living substance precursor according to claim 1, characterized in that: In the active material, the average molar ratio x:y of Fe to Mn is 2:8 to 1:9; The Fe element has a concentration gradient that gradually increases from the central portion to the outer portion; The Mn element has a concentration gradient that gradually decreases from the central portion to the outer portion.

3. A method for preparing a living substance according to claim 2, characterized in that: include: Prepare a metal salt aqueous solution A forming the center portion, including an iron salt solution and a manganese salt solution, and the molar ratio is x1 / y1; A metal salt aqueous solution B for forming the outer surface is prepared, comprising an iron salt solution and a manganese salt solution, and the molar ratio is x2 / y2; wherein x1 / y1<x2 / y2; preparing a mixed solution including an ammonia solution, a phosphoric acid solution or a phosphate solution, and an alkali solution; Adding the metal salt aqueous solution A, aqueous solution C, and the mixed solution into a co-precipitation reactor formed with an inert gas atmosphere to generate seed crystals containing Fe and Mn at a molar ratio of x1 / y1 and containing doping elements; The metal salt aqueous solution A is mixed with the metal salt aqueous solution B to form an aqueous solution whose concentration of Mn element decreases over time, and the aqueous solution is added to the coprecipitation reactor, while adjusting the speed of adding the aqueous solution C to form a core-shell structure crystal with a Mn and Fe concentration gradient and different doping element contents; A carbon source is added into the coprecipitation reactor, and the precursor formed by the reaction is separated, washed with water, and dried to form a carbon-coated active material precursor with a core-shell structure having a concentration gradient. The active material precursor is mixed with a lithium source and a ternary positive electrode material and then sintered at high temperature in an inert gas atmosphere to obtain a composite positive electrode active material.

4. The method for preparing a living substance according to claim 3, characterized in that: When the metal salt aqueous solution A and the metal salt aqueous solution B are mixed and added into the co-precipitation reactor, the mixed solution is continuously added into the co-precipitation reactor.

5. The method for preparing a living substance according to claim 4, characterized in that: When the mixed solution is mixed with the metal salt aqueous solution A, and with the combination of the metal salt aqueous solution A and the metal salt aqueous solution B, the addition acceleration of the ammonia aqueous solution is 1 to 800 mmol / h / L, the addition acceleration of the alkali solution is 1 to 800 mmol / h / L, the addition acceleration of the phosphoric acid solution or the phosphate solution is 1 to 800 mmol / h / L, and the addition acceleration of the aqueous solution C is 0.1 to 8 mmol / h / L.

6. The method for preparing a living substance according to claim 5, characterized in that: The dosing speed of the ammonia solution is 1-100 mmol / h / L, the dosing speed of the alkali solution is 1-100 mmol / h / L, the dosing speed of the phosphoric acid or phosphate solution is 1-100 mmol / h / L, and the dosing speed of the aqueous solution C is 0.8-3.2 mmol / h / L; The addition speeds of the phosphoric acid or phosphate solution, the ammonia solution and the alkaline solution are sequentially reduced to control the concentration of each solution.

7. The method for preparing a living substance according to claim 4, characterized in that: The metal salt aqueous solution A and the mixed solution are reacted at a temperature of 30 to 80° C. for 30 to 40 minutes; 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 30 to 80° C. for at least 20 to 60 hours.

8. The method for preparing a living substance according to claim 3, characterized in that: In the metal salt aqueous solution A and the metal salt aqueous solution B, the cation concentration is 0.5-2 mol / L, the iron salt solution is FeSO4 solution, and the manganese salt solution is MnSO4 solution; In the metal salt aqueous solution A, the molar ratio of FeSO4 to MnSO4 is 2:8 to 0.5:9.5; In the metal salt aqueous solution B, the molar ratio of FeSO4 to MnSO4 is 3:7 to 5:

5.

9. The method for preparing a living substance according to claim 3, characterized in that: The carbon source is glucose, which is processed to form a carbon-coated active material precursor with a core-shell structure having a concentration gradient, and the carbon coating content in the active material precursor is 0.5-3wt%.

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