High-nickel ternary positive electrode material for controlling generation of micro powder and preparation method of high-nickel ternary positive electrode material

Abstract

The preparation method comprises the following steps: uniformly mixing a ternary precursor, a lithium source, a nitrogen source and neodymium fluoride, so as to obtain mixed powder; and carrying out primary sintering, crushing and sieving, washing and filtering, drying and secondary sintering on the mixed powder to obtain the high-nickel ternary positive electrode material. A nitrogen source and neodymium fluoride are added in the raw material mixing stage, and co-doping of N and Nd can inhibit harmful phase change, reduce volume expansion and microcrack generation and regulate diffusion kinetics and surface energy, so that excessive growth of primary crystal grains in the sintering process is inhibited, the structural stability among the crystal grains is improved, generation of micro powder is effectively controlled, and the preparation process is simple. The obtained high-nickel ternary positive electrode material is good in electrochemical energy storage performance and cycling stability and excellent in rate capability.

Description

Technical Field

[0001] The present invention relates to the field of lithium battery materials, and in particular to a high-nickel ternary positive electrode material with controlled micropowder generation and a preparation method thereof. Background Art

[0002] Currently, ternary cathode materials, particularly high-nickel ternary materials (typically with a nickel content of over 60%), are widely used in new energy vehicles, electric bicycles, smart wearable devices, and other fields. Due to their high operating voltage, low production cost, and large reversible capacity, they are considered one of the most promising cathode materials for high-energy-density lithium batteries. However, nickel-rich ternary cathode materials still face some urgent challenges.

[0003] Due to the high nickel content and low sintering temperature, high-nickel ternary cathodes leave a high level of residual alkaline substances (LiOH and Li2CO3) on their surface after sintering. These substances are highly absorbent and easily form a "jelly-like" slurry during the homogenization process, affecting coating uniformity. LiOH reacts with LiPF6 in the electrolyte to produce HF, which corrodes the electrode material. Li2CO3 decomposes under high pressure to produce CO2, which causes battery flatulence. Therefore, the preparation process for high-nickel ternary cathodes generally includes a water washing step to remove residual alkaline substances on the surface, inhibit side reactions, and improve the battery's electrical and cycle performance.

[0004] If the primary grains of the secondary spheres of cathode material obtained after sintering are large and loosely spaced, the mechanical agitation during the subsequent washing and drying processes can cause some primary grains to fall off or small secondary spheres to break apart, resulting in fine powder adhering to the surface of the spheres or scattered within them. Excessive fine powder can lead to battery capacity degradation and reduced rate performance, so an improved process is urgently needed to reduce fine powder generation during the preparation of high-nickel ternary cathode materials. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies, provide a high-nickel ternary positive electrode material and a preparation method thereof that controls the generation of micropowder, and solve the technical problem of excessive micropowder in the high-nickel ternary positive electrode material in the prior art.

[0006] In order to achieve the above technical objectives, the technical solution provided by the present invention is: In a first aspect, the present invention provides a method for preparing a high-nickel ternary positive electrode material with controlled micropowder production, comprising the following steps: uniformly mixing a ternary precursor, a lithium source, a nitrogen source and neodymium fluoride to obtain a mixed powder; subjecting the mixed powder to primary sintering, crushing and screening, water washing and filtering, drying and secondary sintering to obtain a high-nickel ternary positive electrode material.

[0007] In a second aspect, the present invention provides a high-nickel ternary positive electrode material prepared by the above preparation method.

[0008] Compared with the prior art, the present invention has the following beneficial effects: The present invention adds nitrogen source and neodymium fluoride in the raw material mixing stage and then performs a sintering. N and Nd elements as doping elements will directly participate in the synthesis reaction process of the positive electrode material and be integrated into its crystal structure. Among them, N doping can expand the lattice spacing, promote the migration of lithium ions during the charge and discharge process, and reduce the particle size to prevent the primary grains from being too large and easy to fall off; while the addition of Nd can reduce the Li + / Ni 2+ The degree of mixing is increased, thereby making its crystal structure more stable and less prone to microcracks. Therefore, the present invention can inhibit harmful phase changes, reduce volume expansion and microcrack generation, regulate diffusion dynamics and surface energy through co-doping of N and Nd, and thus inhibit excessive growth of primary grains during sintering, thereby improving the structural stability between grains and effectively controlling the generation of micropowder. The high-nickel ternary positive electrode material obtained by the present invention has good electrochemical energy storage performance and cycle stability, and excellent rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a schematic flow chart of a method for preparing a high-nickel ternary cathode material by controlling the generation of micropowders according to the present invention; Figure 2 This is an SEM image of the high-nickel ternary positive electrode material prepared in Example 1 of the present invention; Figure 3 This is an SEM image of the high-nickel ternary positive electrode material prepared in Example 2 of the present invention; Figure 4 This is a SEM image of the high-nickel ternary positive electrode material prepared in Comparative Example 1 of the present invention; Figure 5 The discharge capacity of the battery assembled with the high-nickel ternary cathode material prepared in Examples 1-2 of the present invention and Comparative Example 1 varies with the number of cycles (0.2C); Figure 6 The discharge capacities of batteries assembled with high-nickel ternary cathode materials prepared in Examples 1-2 of the present invention and Comparative Example 1 at different rates are shown. DETAILED DESCRIPTION

[0010] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0011] Currently, during the preparation of high-nickel ternary cathode materials, the large primary grains lead to loose particles. During the washing and drying processes to remove residual alkali, mechanical agitation can easily cause some primary grains to fall off or small secondary spheres to break up, resulting in excessive fine powder. To overcome these drawbacks, the present invention provides a high-nickel ternary cathode material and a preparation method for controlling fine powder production. This improves the preparation process of the high-nickel ternary cathode material by co-doping the raw materials with melamine and neodymium fluoride before sintering to inhibit excessive primary grain growth and improve grain structural stability. Furthermore, air flow agitation is implemented during the washing process to avoid the primary grain shedding and breakage caused by traditional mechanical agitation. Combining these two measures with other steps, the resulting high-nickel ternary cathode material exhibits excellent electrochemical energy storage performance and cycling stability within the normal charge and discharge voltage range. The present invention effectively addresses the drawback of excessive fine powder in high-nickel ternary cathode materials prepared by traditional methods, further improving the electrical properties (including capacity and cycling performance) of the finished product.

[0012] First, see Figure 1 The present invention provides a method for preparing a high-nickel ternary positive electrode material with controlled micropowder production, comprising the following steps: uniformly mixing a ternary precursor, a lithium source, a nitrogen source and neodymium fluoride to obtain a mixed powder; subjecting the mixed powder to primary sintering, crushing and screening, water washing and filtering, drying and secondary sintering to obtain a high-nickel ternary positive electrode material.

[0013] In the present invention, the nitrogen source and neodymium fluoride (NdF3) are added in the raw material mixing stage before the primary sintering, that is, before the crystal structure of the positive electrode material is formed, that is, the N and Nd elements will directly participate in the synthesis reaction process of the positive electrode material and be integrated into its crystal structure to form a dopant. Among them, N doping can expand the lattice spacing, promote the migration of lithium ions during the charge and discharge process, and reduce the particle size to prevent the primary grains from being too large and easy to fall off; while the addition of Nd reduces the Li + / Ni 2+ The degree of mixing makes its crystal structure more stable and less prone to microcracks.

[0014] Preferably, the chemical formula of the ternary precursor is Ni x Co y Mn (1-x-y) (OH)2, 0.80≤x≤0.95, 0.05<y<0.20; the lithium source includes lithium hydroxide (LiOH·H2O).

[0015] Preferably, the molar ratio of the lithium element in the lithium source to the ternary precursor is (1.05-1.07) : 1. The molar amount of the ternary precursor is the total molar amount of nickel, cobalt and manganese.

[0016] Preferably, the nitrogen source includes melamine; in the mixed powder, the concentration of melamine is 1-2% (mol%), and the concentration of neodymium is 0.2-0.4% (wt%).

[0017] In the present invention, the amount of nitrogen source (melamine) and additive (neodymium fluoride) needs to be controlled. Too little melamine will not be able to inhibit the growth of primary grains, while too much will prevent the grains from growing normally, leading to degradation of electrical properties. Too little neodymium fluoride will also not be able to inhibit mixing, while too much will lead to increased costs and the risk of changing its overall structure and thus degrading electrical properties.

[0018] Preferably, the conditions for the primary sintering include: heating to 740-770°C at a heating rate of 5-10°C / min in an oxygen atmosphere with an oxygen concentration of 89-99%, and maintaining the temperature at this temperature for 12-16 hours; wherein the entire calcination process is carried out in a flowing oxygen atmosphere, and heating is stopped after calcination is completed and the furnace is cooled.

[0019] Preferably, the crushing and screening is performed by placing the product in a high-speed crusher for crushing, and then passing the product through a 200-400 mesh screen to separate large particles of foreign matter.

[0020] Preferably, the conditions for water washing and filtration include: adding the crushed and sieved material to pure water at a water-to-material mass ratio of (0.5-0.7) to 1, washing for 6-10 minutes under air flow stirring, and then filtering. It is understood that air flow stirring avoids the shedding and breakage of primary grains caused by traditional mechanical stirring. The specific form is not limited, for example, compressed air is introduced upward from the bottom of a container containing pure water to drive the liquid upward to form an annular vortex, thereby achieving the purpose of stirring and washing. After washing, the water is filtered to remove.

[0021] Preferably, the drying method is vacuum drying, the drying temperature is 150-170° C., and the drying time is 5-6 hours.

[0022] Preferably, the secondary sintering conditions include: heating to 250-290° C. at a heating rate of 5-10° C. / min in an air atmosphere, and maintaining the temperature at this temperature for 8-10 h.

[0023] In a second aspect, the present invention provides a high-nickel ternary positive electrode material prepared by the above preparation method.

[0024] The present invention is further described in detail below through specific examples.

[0025] Example 1 A method for preparing a high nickel ternary cathode material with controlled micropowder production, see Figure 1 , including the following steps: S1. Raw material mixing: Mix appropriate amount of nickel cobalt manganese hydroxide (precursor, Ni0.80Co 0.10 Mn 0.10 A mixed powder was prepared by thoroughly mixing lithium hydroxide (LiOH·H2O), lithium hydroxide (lithium source, LiOH·H2O), melamine (nitrogen source, C3H6N6), and neodymium fluoride (NdF3). The molar ratio of lithium to the total molar amount of nickel, cobalt, and manganese was 1.06:1. The melamine concentration in the mixed powder was controlled to be 1.5 mol%, and the neodymium concentration was controlled to be 0.3 wt%.

[0026] S2. Primary sintering: The mixed powder obtained in S1 is placed in an atmosphere furnace and heated to 750°C at a heating rate of 10°C / min, and then kept at this temperature for 15 hours. The entire calcination process is carried out in a flowing oxygen atmosphere with an oxygen concentration of 89-99%. After calcination is completed, heating is stopped and the mixture is cooled in the furnace to obtain a primary sintered material.

[0027] S3. Crushing and screening: The primary sintered material obtained in S2 is placed in a high-speed crusher for crushing, and then passed through a 400-mesh sieve to separate large particles of foreign matter to obtain a sieved material.

[0028] S4, water washing and filtration: add the sieved material obtained in S3 into a container filled with a certain amount of pure water, so that the water-to-material mass ratio is 0.5:1, and pass compressed air upward from the bottom of the container to drive the liquid to move upward to form an annular vortex, thereby achieving the purpose of stirring and washing. The stirring and washing time is controlled within 6 minutes, and then filtered to remove moisture to obtain the de-alkali material.

[0029] S5. Vacuum drying: the de-alkali material obtained in S4 is placed in a vacuum drying oven for drying. The temperature in the oven is controlled at 150-160° C. and the drying time is controlled at 6 hours to obtain a dried material.

[0030] S6. Secondary sintering: The dried material obtained in S5 is placed in an atmosphere furnace and heated to 260°C at a heating rate of 10°C / min, and then kept at this temperature for 8 hours. The entire calcination process is carried out in an air atmosphere, and the high-nickel ternary positive electrode material is obtained after cooling.

[0031] Example 2 Compared with Example 1, the only difference is that in step S4, ventilation stirring is not used, but traditional motor-driven paddle mechanical stirring is used. Other steps and conditions are the same as those in Example 1.

[0032] Comparative Example 1 Compared with Example 1, the only differences are that: melamine and neodymium fluoride are not added in step S1, and the precursor and lithium source are directly mixed; and in step S4, ventilation stirring is not used, but traditional motor-driven paddle mechanical stirring is used. Other steps and conditions are the same as in Example 1.

[0033] Comparative Example 2 Compared with Example 1, the only difference is that in step S1, melamine is not added, and the other steps and conditions are the same as those in Example 1.

[0034] Comparative Example 3 Compared with Example 1, the only difference is that in step S1, neodymium fluoride is not added, and the other steps and conditions are the same as those in Example 1.

[0035] Performance Testing 1. The surface morphologies of Example 1, Example 2 and Comparative Example 1 were observed by scanning electron microscopy; the results were as follows: Figures 2 to 4 shown.

[0036] Depend on Figure 2 It can be seen that the secondary particles of the high nickel ternary positive electrode material obtained in Example 1 are distributed relatively evenly, and there are no obvious primary particles falling or broken secondary particles between the secondary particles; Figure 3 It can be seen that in Example 2, air flow stirring was not used but traditional mechanical stirring was used, and a small amount of secondary particles were broken or primary particles fell off; Figure 4 In Comparative Example 1 shown, melamine and neodymium fluoride were not added and mechanical stirring was used, and the amount of fine powder smaller than 1 μm in the obtained high-nickel ternary positive electrode material increased significantly.

[0037] 2. Assemble button cells using positive electrode sheets, lithium metal sheets (negative electrode sheets) and electrolytes in an argon-filled glove box. Test the cycle performance and rate performance of the button cells at a charge and discharge voltage of 2.7-4.4V on a battery testing system. The preparation method of the positive electrode sheet is as follows: First, 80% of the positive electrode material obtained in the above-mentioned embodiment or comparative example, 10% of acetylene black (conductive agent) and 10% of polyvinylidene fluoride (PVDF) (binder) are thoroughly mixed and stirred for 4 hours. The resulting slurry is evenly coated on aluminum foil and dried in a vacuum oven at 120°C for 12 hours. The aluminum foil after the slurry is dried is then punched into a disc with a diameter of 12 mm. The electrolyte is 1 mol / L lithium hexafluorophosphate (LiPF6) dissolved in a mixture of ethyl carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC=1:1 volume ratio). All electrochemical measurements are performed at room temperature. The test results are as follows. Figure 5-Figure 6 And shown in Table 1.

[0038] Table 1 Electrical properties of button cells of comparative examples and examples (0.2C)

[0039] Depend on Figure 5 As can be seen from Table 1, the batteries assembled with the positive electrode materials obtained in Examples 1 and 2 of the present invention have high capacity and high discharge efficiency, especially the 52-cycle efficiency of Example 1 is stable; in Comparative Example 1, no melamine and neodymium fluoride are added and mechanical stirring is adopted, and the first discharge capacity of the battery assembled with the positive electrode material decreases significantly, resulting in a charge and discharge efficiency that is significantly lower than that of Example 1; Comparative Example 2 does not add melamine, and Comparative Example 3 does not add neodymium fluoride, and the performance of the battery assembled with the obtained positive electrode materials is worse than that of Example 1, but better than that of Comparative Example 1, which shows that the present invention adopts airflow stirring combined with co-doping of melamine and neodymium fluoride to synergistically improve the capacity (especially the discharge capacity) of the positive electrode material, thereby improving the charge and discharge efficiency and effectively improving the cycle performance.

[0040] Depend on Figure 6 It can be seen that as the number of cycles increases (within 25 times), the discharge capacity of the battery assembled with the positive electrode material obtained in Example 1 can still be maintained above 140 mAh / g under 5C conditions, and that of Example 2 can also be maintained at around 130 mAh / g, while that of Comparative Example 1 drops to around 105 mAh / g, indicating that the present invention uses airflow stirring combined with co-doping of melamine and neodymium fluoride to synergistically improve the high current rate performance of the positive electrode material.

[0041] In summary, the present invention adds a nitrogen source and neodymium fluoride during the raw material mixing stage, and co-doping of N and Nd can inhibit harmful phase changes, reduce volume expansion and microcrack generation, regulate diffusion dynamics and surface energy, and thus inhibit excessive growth of primary grains during sintering to improve the structural stability between grains; in addition, the present invention adopts a ventilation stirring method to drive the flow of liquid through rising bubbles, avoiding the strong shear force generated by the high-speed rotation of mechanical blades, reducing crystal breakage or structural defects, and eliminating pollution problems caused by metal blade wear (such as stainless steel blades releasing Fe) or sealing material falling off.

[0042] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a high-nickel ternary cathode material with controlled micropowder generation, characterized in that: The following steps are involved: The ternary precursor, the lithium source, the nitrogen source and the neodymium fluoride are uniformly mixed to obtain a mixed powder; The mixed powder is subjected to primary sintering, crushing and screening, water washing and filtering, drying and secondary sintering to obtain a high-nickel ternary positive electrode material.

2. The method for preparing a high-nickel ternary cathode material with controlled micropowder generation according to claim 1, characterized in that: The chemical formula of the ternary precursor is Ni x Co y Mn (1-x-y) (OH)2, 0.80≤x≤0.95, 0.05<y<0.20; the lithium source includes lithium hydroxide.

3. The method for preparing a high-nickel ternary cathode material with controlled micropowder generation according to claim 1, characterized in that: The molar ratio of the lithium element in the lithium source to the ternary precursor is (1.05-1.07):

1.

4. The method for preparing a high-nickel ternary cathode material with controlled micropowder generation according to claim 1, characterized in that: The nitrogen source includes melamine; in the mixed powder, the concentration of melamine is 1 to 2 mol%, and the concentration of neodymium is 0.2 to 0.4 wt%.

5. The method for preparing a high-nickel ternary cathode material with controlled micropowder generation according to claim 1, characterized in that: The primary sintering conditions include: heating to 740-770° C. at a heating rate of 5-10° C. / min and holding for 12-16 hours in an oxygen atmosphere with an oxygen concentration of 89-99%.

6. The method for preparing a high-nickel ternary cathode material with controlled micropowder generation according to claim 1, characterized in that: The 200-400 mesh screen is used in the crushing and screening.

7. The method for preparing a high-nickel ternary cathode material with controlled micropowder generation according to claim 1, characterized in that: The conditions for water washing and filtration include: adding the crushed and sieved material into pure water at a water-to-material mass ratio of (0.5-0.7):1, washing for 6-10 minutes under air flow stirring, and then filtering.

8. The method for preparing a high-nickel ternary cathode material with controlled micropowder generation according to claim 1, characterized in that: The drying method is vacuum drying, the drying temperature is 150-170° C., and the drying time is 5-6 hours.

9. The method for preparing a high-nickel ternary cathode material with controlled micropowder generation according to claim 1, characterized in that: The secondary sintering conditions include: heating to 250-290° C. at a heating rate of 5-10° C. / min and keeping the temperature for 8-10 h in an air atmosphere.

10. A high-nickel ternary positive electrode material prepared by the preparation method according to any one of claims 1 to 9.

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