Preparation method of sodium ion battery precursor and cathode with simple harmonic concentration gradient structure

Abstract

The present invention discloses a preparation method of a sodium-ion battery precursor and a cathode with a simple harmonic concentration gradient structure, belonging to the field of sodium-ion battery cathode materials. To solve the problems of multiple complex phase transitions and poor long-cycle performance of current sodium-ion battery cathodes, the present invention proposes a preparation method of a novel concentration gradient structure precursor, in which the metal ion concentration follows a simple harmonic variation law. The precursor prepared by this method is equivalent to rearranging the traditional linear concentration gradient precursor after differentiating it along the radial direction, successfully distributing the originally stable surface layer into the bulk phase, and also ensuring the high-capacity characteristics of the original core. The cathode material fired from the precursor greatly improves the stability of the sodium-ion battery. The process flow is simple and controllable, with low cost, and is suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to a preparation method of a sodium-ion battery cathode with a harmonic concentration gradient precursor and a cathode. Background Art

[0002] Among sodium-ion battery cathode materials, sodium element is widely distributed globally, has huge reserves and low cost, which enables sodium-ion batteries to have great market potential and has received extensive attention from the academic and industrial circles in the battery field. And layered oxide cathodes have become the sodium-ion battery cathodes closest to commercialization due to their high specific capacity and safety. However, there are still some key challenges in the cycle, rate, processing, etc. of sodium-ion battery layered oxide cathodes. Due to complex multiple phase transitions, air stability, and limitations of the precursor morphology and structure, the capacity of the material rapidly decays during the cycle, which seriously hinders the further application of this layered oxide material. To solve these problems, the academic and industrial circles have made various modification attempts on the material, such as plasma phase doping, surface doping, surface coating, structure design, etc.

[0003] Therefore, the present invention uses wet chemical co-precipitation to conduct multi-stage gradient design on the precursor of the sodium-ion battery layered oxide cathode, so that the high-capacity structure and the high-stability structure are alternately distributed, and a series of sodium-ion battery layered oxide cathode materials with excellent cycle stability are developed. This preparation method has a simple production process and reasonable cost, and is suitable for large-scale industrial production. Summary of the Invention<(

[0004] Aiming at the key challenges existing in sodium-ion battery layered oxides, the present invention conducts a reasonable structural design on the precursor of its cathode material and prepares it into a cathode material.

[0005] To achieve the above object, metal ions are subjected to multi-stage gradient co-precipitation by wet chemical co-precipitation, so that the concentration gradient is distributed in a harmonic periodic manner, and the double-layer (or multi-layer) high-capacity and high-stability structures are alternately arranged. The manganese concentration shows a trend of first rising, then falling, and then rising, and the nickel concentration shows a trend of first falling, then rising, and then falling. And an appropriate amount of magnesium and cobalt ions are selectively incorporated to improve the multiple complex phase transitions of the material and enhance the high-voltage and long-cycle performance.

[0006] Specifically, it includes the following steps:

[0007] (1) Prepare metal salt solutions M1, M2, and M3; prepare a precipitant solution A; prepare a complexing agent solution B; the precipitant solution is a sodium hydroxide solution, and the complexing agent solution is an ammonia water solution;

[0008] (2) Prepare the bottom liquid of the reaction kettle;

[0009] (3) Add metal salt solution M1, complexing agent solution A and precipitant solution B to the reactor in parallel, and add metal salt solution M3 to M1 solution at an appropriate flow rate; when the particle size of the reaction slurry reaches the set value L1, stop adding metal salt solution M3 and add M2 solution to M1 solution instead; when the particle size of the reaction slurry reaches the value L2, stop adding M2 solution and add metal salt solution M3 to M1 solution instead; the above operation can be repeated N times to set different particle size values Lm; during the entire reaction process, the pH value of the reaction system is controlled to be 8.5-11 and the ammonia concentration is controlled to be 6.5-10.5 g / L;

[0010] (4) When the particle size of the reaction slurry reaches the target value, the reaction is stopped; the slurry after the coprecipitation reaction is filtered, and the solid phase powder is washed and dried to obtain a precursor material with a quasi-simple harmonic concentration gradient.

[0011] (5) The obtained precursor is fully and evenly mixed with sodium salt and sintered to obtain a positive electrode material with a quasi-simple harmonic concentration gradient.

[0012] Preferably, the concentrations of the prepared metal salt solutions M1 and M2 are 1 mol / L to 4 mol / L, wherein the ion molar ratio of manganese ions, nickel ions, cobalt ions and magnesium ions is x1:y1:z1:w1 (x1∈[0,0.6], z1∈[0,0.1], w1∈[0,0.1], y1=1-x1-z1-w1), and the concentrations of the components M1 and M2 are the same; the concentration of the prepared metal salt solution M3 is 1 mol / L to 4 mol / L, wherein the ion molar ratio of manganese ions, nickel ions, cobalt ions and magnesium ions is x2:y2:z2:w2 (0.1≤x2-x1≤0.7 and x2≤0.7, z2=z1, w2=w1, y2=1-x2-z2-w2);

[0013] Preferably, the precipitant A is a sodium hydroxide solution with a concentration of 1 to 4 mol / L; the complexing agent B is an ammonia solution with a concentration of 6.5 to 10.5 g / L; the stirring speed is 280 rpm to 480 rpm;

[0014] Preferably, the metal salt solution is one or more of a nitrate solution, a chloride solution, a sulfate solution, an acetate solution, and an oxalate solution.

[0015] Preferably, the pH range of the reaction system is 8.5-11; the ammonia concentration is 6.5-10.5 g / L.

[0016] Preferably, the particle size setting value L1 is 1 / 5-1 / 3 of the target precursor particle size; the setting value L2 is 2 / 5-2 / 3 of the target precursor particle size; the setting value Lm can be determined according to the number of repetitions N and the target precursor particle size, N≥1; the target precursor particle size is 3~10um.

[0017] Preferably, the injection rates of the metal salt solution M3 and the metal salt solution M2 are determined according to the coprecipitation rate and the injection rate of the metal salt solution M1; the stirring rate in the metal salt solution M1 is 280 rpm to 480 rpm.

[0018] Preferably, in the metal salt solution, the molar contents of cobalt and magnesium are not higher than 10%.

[0019] Preferably, the sodium salts for mixed sodium sintering in the present invention are at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium citrate, sodium acetate, sodium oxalate, sodium oxide, sodium peroxide, and sodium superoxide.

[0020] Preferably, the temperature range for mixed sodium sintering is 500 - 1100 °C.

[0021] The precursor designed in the present invention has a multi-layer structure, and the metal ion concentration in the precursor follows the law of quasi-simple harmonic variation. When N = 1, the manganese concentration shows a trend of first rising, then falling, and then rising, the nickel concentration shows a trend of first falling, then rising, and then falling, and cobalt and magnesium are doped in small amounts. The cathode material sintered after the precursor and the sodium salt are fully and uniformly mixed improves the high voltage and cycling performance of the sodium-ion battery. The precursor prepared by this method is equivalent to rearranging the traditional linear concentration gradient precursor after differentiating it along the radial direction, successfully distributing the originally stable surface layer into the bulk phase, and also ensuring the high-capacity characteristics of the original core. The process flow is simple and controllable, with low cost, and is suitable for large-scale production. Description of the Drawings

[0022] Figure 1 is the XRD pattern of the cathode precursor material prepared in Example 2 of the present invention.

[0023] Figure 2 is the XRD pattern of the cathode layered oxide material prepared in Example 2 of the present invention.

[0024] Figure 3 is the SEM image of the cathode layered oxide material prepared in Example 2 of the present invention.

[0025] Figure 4 is the electrochemical cycling curve of the cathode layered oxide material prepared in Example 2 of the present invention. Detailed Embodiments

[0026] To make the technical problems, technical solutions, and advantages to be solved by the present invention clearer, the following will be described in detail with reference to specific embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0027] Unless otherwise defined, all technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0028] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0029] Example 1

[0030] (1) Prepare sulfate solutions M1 and M2 with a total metal concentration of manganese and nickel of 4 mol / L, and the molar ratio of manganese to nickel in the sulfate solution is 1:1; prepare a sulfate solution M3 with a total metal concentration of manganese and nickel of 4 mol / L, and the molar ratio of manganese to nickel in the sulfate solution is 7:3; prepare a 3 mol / L sodium hydroxide solution; prepare a 3 mol / L ammonia water solution; prepare a reaction kettle bottom liquid, adjust the pH to 10, the ammonia concentration to 6 g / L, and introduce nitrogen; inject M1 into the reaction kettle at a rate of 60 ml / min, inject M3 into M1 at a rate of 40 ml / min. When the particle size reaches 1.6 um, stop adding M3 and change to adding M2 to M1 at a rate of 40 ml / min. When the particle size reaches 3.2 um, stop adding M2 and change to adding M3 at the same rate as before. When the particle size reaches 5 um, stop the reaction. Filter, wash, and dry the slurry to obtain the precursor. The stirring speed is 300 rpm.

[0031] (2) Take 10 g of the precursor under the condition that the molar ratio of sodium to transition metal is 0.67 and sodium is in excess by 3%. Weigh a certain mass of anhydrous sodium carbonate powder and mix it in a ball mill for 1 h at a speed of 350 rpm; then transfer the powder to a muffle furnace and sinter it at 500 °C for 6 h and at 900 °C for 12 h, and cool it naturally to obtain the cathode material.

[0032] For the cathode material prepared in Example 1, in the voltage range of 2 - 4.5 V and under the condition of a 1C rate, the initial discharge capacity in the first cycle reaches 122 mAh / g, and the capacity retention rate after 50 cycles is 94%; and under the condition of 0.1C, the initial discharge capacity reaches 141 mAh / g. In the voltage range of 2 - 4 V and under the condition of a 1C rate, the capacity retention rate after 50 cycles reaches 100%.

[0033] Example 2

[0034] The difference between Example 2 and Example 1 is only that: only 10% molar proportion of magnesium ions is added.

[0035] (1) Prepare sulfate solutions M1 and M2 with a total metal concentration of manganese, nickel, and magnesium of 4 mol / L, and the molar ratio of manganese, nickel, and magnesium in the sulfate solution is 4.5:4.5:1; prepare a sulfate solution M3 with a total metal concentration of manganese, nickel, and magnesium of 4 mol / L, and the molar ratio of manganese, nickel, and magnesium in the sulfate solution is 6.3:2.7:1; prepare a 3 mol / L sodium hydroxide solution; prepare a 3 mol / L ammonia water solution; prepare the bottom liquid of the reaction kettle, adjust the pH to 10, the ammonia concentration to 6 g / L, and introduce nitrogen; inject M1 into the reaction kettle at a rate of 60 ml / min, inject M3 into M1 at a rate of 40 ml / min. When the particle size reaches 1.6 um, stop adding M3 and change to adding M2 to M1 at a rate of 40 ml / min. When the particle size reaches 3.2 um, stop adding M2 and change to adding M3 at the same rate as before. When the particle size reaches 5 um, stop the reaction. Filter, wash, and dry the slurry to obtain the precursor. The stirring speed is 300 rpm for all steps.

[0036] (2) Take 10 g of the precursor and, under the condition that the molar ratio of sodium to transition metals is 0.67 and sodium is in excess by 3%, weigh a certain mass of anhydrous sodium carbonate powder and mix it in a ball mill for 1 h at a speed of 350 rpm; then transfer the powder to a muffle furnace and sinter it at 500 °C for 6 h and at 900 °C for 12 h, and cool it naturally to obtain the cathode material.

[0037] For the cathode material prepared in Example 2, in the voltage range of 2 - 4.5 V and under the condition of a 1C rate, the initial discharge capacity in the first cycle reaches 117 mAh / g, and the capacity retention rate after 50 cycles is 97%; and under the condition of 0.1C, the initial discharge capacity reaches 141 mAh / g. In the voltage range of 2 - 4 V and under the condition of a 1C rate, the capacity retention rate after 50 cycles reaches 100%.

[0038] Example 3

[0039] The difference between Example 3 and Example 1 is only that: only 10% molar proportion of magnesium ions and 10% molar proportion of cobalt ions are added.

[0040] (1) Prepare sulfate solutions M1 and M2 with a total metal concentration of 4 mol / L of manganese, nickel, magnesium, and cobalt, and the molar ratio of manganese, nickel, magnesium, and cobalt in the sulfate solution is 4:4:1:1; prepare sulfate solution M3 with a total metal concentration of 4 mol / L of manganese, nickel, magnesium, and cobalt, and the molar ratio of manganese, nickel, magnesium, and cobalt in the sulfate solution is 5.6:2.4:1:1; prepare 3 mol / L sodium hydroxide solution; prepare 3 mol / L ammonia solution; prepare the reaction kettle bottom liquid, adjust the pH to 10, the ammonia concentration is 6 g / L, and introduce nitrogen; inject M1 into the reaction kettle at a rate of 60 ml / min, inject M3 into M1 at a rate of 40 ml / min. When the particle size reaches 1.6 um, stop adding M3 and instead add M2 to M1 at a rate of 40 ml / min. When the particle size reaches 3.2 um, stop adding M2 and instead add M3 at the same rate as before. When the particle size reaches 5 um, stop the reaction. Filter, wash, and dry the slurry to obtain the precursor. The stirring speed is 300 rpm for all cases.

[0041] (2) Take 10 g of the precursor under the condition that the molar ratio of sodium to transition metals is 0.67 and sodium is in excess by 3%. Weigh a certain mass of anhydrous sodium carbonate powder and mix it in a ball mill for 1 h at a speed of 350 rpm; then transfer the powder to a muffle furnace and sinter it at 500 °C for 6 h and at 900 °C for 12 h, and cool it naturally to obtain the cathode material.

[0042] For the cathode material prepared in Example 3, in the voltage range of 2 - 4.5 V and under the condition of a 1C rate, the initial discharge capacity in the first cycle reaches 128 mAh / g, and the capacity retention rate after 50 cycles is 96%; and under the condition of 0.1C, the initial discharge capacity reaches 142 mAh / g. In the voltage range of 2 - 4 V and under the condition of a 1C rate, the capacity retention rate after 50 cycles reaches 100%.

[0043] Comparative Example 1

[0044] (1) Prepare sulfate solution M with a total metal concentration of 4 mol / L of manganese, nickel, and magnesium, and the molar ratio of manganese to nickel in the sulfate solution is 7:3; prepare 3 mol / L sodium hydroxide solution; prepare 3 mol / L ammonia solution; prepare the reaction kettle bottom liquid, adjust the pH to 10, the ammonia concentration is 6 g / L, and introduce nitrogen; inject M into the reaction kettle at a rate of 60 ml / min. When the particle size reaches 5 um, stop the reaction. Filter, wash, and dry the slurry to obtain the precursor. The stirring speed is 300 rpm for all cases.

[0045] (2) Take 10 g of the precursor under the condition that the molar ratio of sodium to transition metal is 0.67 and sodium is in excess by 3%. Weigh a certain mass of anhydrous sodium carbonate powder and mix it in a ball mill for 1 h at a rotation speed of 350 rpm. Then transfer the powder to a muffle furnace and sinter it at 500 °C for 6 h and at 900 °C for 12 h. After natural cooling, the cathode material is obtained.

[0046] For the cathode material prepared in Comparative Example 1, in the voltage range of 2 - 4.5 V and under the condition of a 1C rate, the initial discharge capacity in the first cycle reaches 145 mAh / g, and the capacity retention rate after 50 cycles is 80%; and under the condition of 0.1C, the initial discharge capacity reaches 170 mAh / g. In the voltage range of 2 - 4 V and under the condition of a 1C rate, the capacity retention rate after 50 cycles reaches 97%.

[0047] The above-described embodiments are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope of the present invention, according to the technical solution and its concept of the present invention, makes equivalent substitutions or changes, and all should be covered by the protection scope of the present invention.

Claims

1. A preparation method of a sodium-ion battery precursor with a simple harmonic concentration gradient structure, characterized in that, It includes the following steps: Step S1, prepare metal salt solutions M1, M2, and M3; Prepare a complexing agent solution A and a precipitating agent solution B; the complexing agent solution is an ammonia water solution; the metal salts are at least one of cobalt and magnesium salts and manganese and nickel salts, and the components of M1 and M2 solutions are the same, and the ionic mole numbers in the solutions are the same. The components of M1 and M3 solutions are the same, but the ionic mole numbers in the solutions are different; Step S2, prepare the bottom liquid of the reaction kettle and keep the inside of the kettle in a nitrogen atmosphere; Step S3, add the metal salt solution M1, the complexing agent solution A, and the precipitating agent solution B into the reaction kettle in parallel flow, and add the metal salt solution M3 into the M1 solution at an appropriate flow rate; when the particle size of the reaction slurry reaches the set value L1, stop adding the metal salt solution M3 and change to adding the M2 solution into the M1 solution; when the particle size of the reaction slurry reaches the value L2, stop adding the M2 solution and change to adding the metal salt solution M3 into the M1 solution; the above operations can be repeated N times to set different particle size values Lm; during the whole reaction process, control the pH value of the reaction system to be 8.5 - 11 and the ammonia concentration to be 6.5 - 10.5 g / L; Step S4, when the particle size of the reaction slurry reaches the target value, stop the reaction; filter the slurry after the coprecipitation reaction, wash and dry the solid-phase powder to obtain a precursor material with a quasi-harmonic concentration gradient; The precursor is a multi-layer structure, and the manganese concentration shows a trend of first rising, then falling, and then rising, while the nickel concentration shows a trend of first falling, then rising, and then falling.

2. The preparation method of a sodium ion battery precursor with a simple harmonic concentration gradient structure as described in claim 1, characterized in that, The concentrations of the prepared metal salt solutions M1 and M2 are 1 mol / L - 4 mol / L, and the ionic mole ratios of manganese ions, nickel ions, cobalt ions, and magnesium ions are x1:y1:z1:w1, where x1 ∈ [0, 0.6], z1 ∈ [0, 0.1], w1 ∈ [0, 0.1], and y1 = 1 - x1 - z1 - w1, and the component concentrations of M1 and M2 are the same; the concentration of the prepared metal salt solution M3 is 1 mol / L - 4 mol / L, and the ionic mole ratios of manganese ions, nickel ions, cobalt ions, and magnesium ions are x2:y2:z2:w2, where 0.1 ≤ x2 - x1 ≤ 0.7 and x2 ≤ 0.7, z2 = z1, w2 = w1, and y2 = 1 - x2 - z2 - w2; the precipitating agent A is a sodium hydroxide solution with a concentration of 1 - 4 mol / L; the complexing agent B is an ammonia water solution with a concentration of 6.5 - 10.5 g / L; the stirring speed is 280 rpm - 480 rpm.

3. The preparation method of a sodium ion battery precursor with a simple harmonic concentration gradient structure as described in claim 1, characterized in that, The metal salt solution is one or more of a nitrate solution, a chloride solution, a sulfate solution, an acetate solution, and an oxalate solution.

4. The preparation method of a sodium ion battery precursor with a simple harmonic concentration gradient structure as described in claim 1, characterized in that, The set value L1 of the particle size is 1 / 5 - 1 / 3 of the target precursor particle size; the set value L2 is 2 / 5 - 2 / 3 of the target precursor particle size; the set value Lm is determined according to the repetition times N and the target precursor particle size, N ≥ 1; the target precursor particle size is 3 - 10 μm.

5. The preparation method of a sodium-ion battery precursor having a simple harmonic concentration gradient structure as described in claim 1, wherein, The injection rates of the metal salt solution M3 and the metal salt solution M2 are determined according to the coprecipitation rate and the injection rate of the metal salt solution M1; the stirring speed in the metal salt solution M1 is 280 rpm - 480 rpm.

6. The preparation method of a sodium ion battery precursor with a simple harmonic concentration gradient structure according to claim 2, characterized in that, In the metal salt solution, the molar contents of cobalt and magnesium are not higher than 10%.

7. A preparation method of a cathode material for a sodium ion battery with a simple harmonic concentration gradient structure, characterized in that, It is made by sintering the precursor mixture of sodium with a simple harmonic concentration gradient structure prepared by the precursor preparation method according to any one of claims 1-6.

8. The preparation method of a cathode material for a sodium ion battery with a simple harmonic concentration gradient structure as claimed in claim 7, wherein The sodium salt is at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium citrate, sodium acetate, sodium oxalate, sodium oxide, sodium peroxide, and sodium superoxide, and the temperature range of the mixed sodium sintering is 500-1100 °C.

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