A modified cathode precursor, its preparation method and application

Abstract

This invention provides a modified cathode precursor, its preparation method, and its application. The preparation method includes the following steps: (1) mixing a nickel-cobalt-manganese ternary salt solution with a zirconium salt to obtain a zirconium-doped ternary salt solution; (2) injecting the zirconium-doped ternary salt solution, a precipitant, and a complexing agent into the base solution in a co-precipitation reaction; (3) keeping the injection rates of the precipitant and the complexing agent constant, reducing the injection rate of the zirconium-doped ternary salt solution, and injecting it into an aluminum-containing salt solution in a co-precipitation reaction to obtain the modified cathode precursor. In the early stage of this invention, the doping element and the ternary solution are mixed and fed together. The proportion of the ternary solution and the concentration of the doping element in the solution are adjusted in the early stage. After the coprecipitation begins, the concentration or flow rate of the doping element does not need to be adjusted. After reaching a certain particle size, the coating element and the ternary material are fed together. The feed flow rate is adjusted according to the amount of coating element to obtain a uniformly doped and coated ternary precursor with both anion and cation doping.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a modified cathode precursor, its preparation method and application. Background Technology

[0002] In recent years, significant progress has been made in the research and industrialization of ternary lithium-ion batteries, and the industry generally believes that NCM batteries will become the mainstream choice for future electric vehicles. Generally speaking, based on safety and cycle performance considerations, ternary lithium-ion batteries mainly use series with relatively low nickel content, such as 333, 442, and 523. However, as EVs demand increasingly higher energy density, the nickel content in ternary materials is gradually increasing.

[0003] Increasing the nickel content in ternary materials leads to higher energy density, but it is well known that higher nickel content in ternary materials results in lower stability and safety. To address this issue, one approach is to dope the material. Doping the ternary material lattice with metal ions can suppress Li / Ni cation mixing, helping to reduce the initial irreversible capacity. Metal ion doping can also make the layered structure more complete, thus helping to increase the rate capability. Furthermore, it can improve the stability of the ternary material structure and enhance cycling performance.

[0004] CN105680030A discloses a method for preparing a nickel-cobalt-manganese ternary cathode material precursor, belonging to the field of electrochemical technology, including the following steps: preparing a nickel-cobalt-manganese salt solution with a metal ion concentration of 60-120 g / L, preparing a sodium hydroxide solution of 160-240 g / L, and an ammonia solution with a mass concentration of 10-18%; adding deionized water to a sealed reaction vessel, stirring, purging with nitrogen, adding ammonia solution, and adjusting the ammonia solution concentration to 0.3-1.0 mol / L; heating to 50-70℃, simultaneously adding the nickel-cobalt-manganese salt solution, sodium hydroxide solution, and ammonia solution to the reaction vessel, controlling the pH to 10-12, and controlling the ammonia solution concentration to 0.3-1.0 mol / L; after the addition is complete, stopping stirring, aging for 1 hour, and removing the upper clear mother liquor under sealed conditions; stirring again, and repeating precipitation until the particle size reaches the required particle size.

[0005] CN112054182A discloses a lithium nickel cobalt manganese oxide ternary precursor, its preparation method, and a lithium nickel cobalt manganese oxide cathode material. The method includes: 1) dissolving and mixing a nickel source, a cobalt source, a manganese source, and urea to obtain a solution A; dissolving a lithium source to obtain a solution B; 2) adding the solutions A and B to a high-pressure reactor for reaction; 3) filtering and washing the solution obtained in step 2) to obtain a filter cake as the lithium nickel cobalt manganese oxide ternary precursor.

[0006] The aforementioned method for preparing the precursor suffers from drawbacks such as poor uniformity after sintering, high energy consumption, and numerous processing steps. Therefore, there is an urgent need to develop a method for preparing the cathode precursor to improve doping uniformity, increase coating efficiency, reduce sintering steps, and enhance the electrochemical performance of the cathode material. Summary of the Invention

[0007] The purpose of this invention is to provide a modified cathode precursor, its preparation method, and its application. In the early stage, this invention adopts a mixed feeding method of doping elements and ternary solution. The proportion of ternary solution and the concentration of doping elements in the solution are adjusted in the early stage. After co-precipitation begins, there is no need to adjust the concentration or flow rate of doping elements. After a certain particle size is reached, the coating elements and ternary materials are fed together. By adjusting the feed flow rate according to the amount of coating elements, a uniform cation and anion dual-doped internally doped and externally coated ternary precursor can be obtained.

[0008] To achieve this objective, the present invention employs the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a modified cathode precursor, the method comprising the following steps:

[0010] (1) Mix the nickel-cobalt-manganese ternary salt solution with zirconium salt to obtain a zirconium-doped ternary salt solution;

[0011] (2) A one-step co-precipitation reaction was carried out by injecting zirconium-doped ternary salt solution, precipitant and complexing agent into the bottom liquid in a co-flow manner;

[0012] (3) The injection rates of the precipitant and complexing agent remain unchanged, while the injection rate of the zirconium-doped ternary salt solution is reduced and the aluminum-containing salt solution is injected in parallel to carry out a two-step co-precipitation reaction to obtain the modified cathode precursor.

[0013] This invention pre-mixes the nickel-cobalt-manganese ternary salt solution with zirconium salt for simultaneous feeding, while Al raw material is fed separately. This reduces redundant processes and lowers costs, while effectively stabilizing the Zr and Al content in nickel-cobalt-manganese. The existing mature ammonia co-precipitation process can be used, reducing process modifications and lowering costs.

[0014] Preferably, the elemental molar ratio of nickel, cobalt, and manganese in the nickel-cobalt-manganese ternary salt solution in step (1) is Ni:Co:Mn=x:y:0.3, 0.5≤x<0.7, 0 <y≤0.2,0.3+x+y=1。

[0015] Preferably, the total concentration of metal ions in the nickel-cobalt-manganese ternary salt solution is 1.5 to 2 mol / L, for example: 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L or 2 mol / L, etc.

[0016] Preferably, the concentration of zirconium in the zirconium-doped ternary salt solution in step (1) is 2 to 8 mmol / L, for example: 2 mmol / L, 3 mmol / L, 5 mmol / L, 6 mmol / L or 8 mmol / L, etc.

[0017] Preferably, the precipitant in step (2) includes a sodium hydroxide solution and / or a potassium hydroxide solution.

[0018] Preferably, the concentration of the precipitant is 7 to 9 mol / L, for example: 7 mol / L, 7.5 mol / L, 8 mol / L, 8.5 mol / L or 9 mol / L, etc.

[0019] Preferably, the complexing agent comprises ammonia.

[0020] Preferably, the concentration of the complexing agent is 4.5 to 5 mol / L, for example: 4.5 mol / L, 4.6 mol / L, 4.8 mol / L, 4.9 mol / L or 5 mol / L, etc.

[0021] Preferably, the flow rate of the zirconium-doped ternary salt solution is 35–60 L / h, for example: 35 L / h, 40 L / h, 45 L / h, 50 L / h, or 60 L / h.

[0022] Preferably, the flow rate of the precipitant is 10-20 L / h, for example: 10 L / h, 12 L / h, 15 L / h, 18 L / h or 20 L / h, etc.

[0023] Preferably, the flow rate of the complexing agent is 2.5 to 5.5 L / h, for example: 2.5 L / h, 3 L / h, 4 L / h, 5 L / h or 5.5 L / h.

[0024] Preferably, the temperature of the one-step coprecipitation reaction in step (2) is 40 to 70°C, for example: 40°C, 45°C, 50°C, 60°C or 70°C.

[0025] Preferably, the stirring speed of the one-step coprecipitation reaction is 250 to 400 rpm, for example: 250 rpm, 280 rpm, 300 rpm, 350 rpm or 400 rpm.

[0026] Preferably, the pH of the one-step coprecipitation reaction is 9.5 to 12, for example: 9.5, 10, 10.5, 11 or 12, etc.

[0027] Preferably, the endpoint of the one-step coprecipitation reaction is when the particle size in the system is 3 to 4 μm, for example: 3 μm, 3.2 μm, 3.5 μm, 3.8 μm or 4 μm, etc.

[0028] Preferably, the flow rate of the zirconium-doped ternary salt solution in step (3) is 15 to 35 L / h, for example: 15 L / h, 18 L / h, 20 L / h, 30 L / h or 35 L / h.

[0029] Preferably, the solute in the aluminum salt solution includes any one or a combination of at least two of sodium aluminate, aluminum sulfate, or aluminum nitrate.

[0030] Preferably, the concentration of aluminum in the aluminum-containing salt solution is 1 to 2 mol / L, for example: 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L or 2 mol / L, etc.

[0031] Preferably, the flow rate of the aluminum salt solution is 30-60 L / h, for example: 30 L / h, 35 L / h, 40 L / h, 50 L / h or 60 L / h.

[0032] Preferably, the temperature of the two-step coprecipitation reaction in step (3) is 40 to 70°C, for example: 40°C, 45°C, 50°C, 60°C or 70°C.

[0033] Preferably, the stirring speed of the two-step coprecipitation reaction is 250-400 rpm, for example: 250 rpm, 280 rpm, 300 rpm, 350 rpm or 400 rpm.

[0034] Preferably, the pH of the two-step coprecipitation reaction is 9.5 to 12, for example: 9.5, 10, 10.5, 11 or 12.

[0035] Preferably, the two-step coprecipitation reaction is followed by washing and drying.

[0036] Preferably, the detergent used for washing includes hot water and liquid alkali.

[0037] In a second aspect, the present invention provides a modified cathode precursor, which is prepared by the method described in the first aspect.

[0038] Thirdly, the present invention provides a cathode material, which is prepared by mixing and sintering a modified cathode precursor as described in the second aspect with a lithium source.

[0039] Fourthly, the present invention provides a lithium-ion battery comprising the positive electrode material as described in the third aspect.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) In the early stage of this invention, the doping element and the ternary solution are mixed and fed together. The ratio of the ternary solution and the concentration of the doping element in the solution are adjusted in the early stage. After the co-precipitation begins, there is no need to adjust the concentration or flow rate of the doping element. After a certain particle size is reached, the coating element and the ternary material are fed together. The feed flow rate is adjusted according to the amount of coating element to obtain a uniform ternary precursor with internal doping and external coating of anion and cation doping.

[0042] (2) The modified cathode precursor of the present invention can maintain a capacity retention rate of more than 85.1% after 100 cycles. When Zr is doped in an appropriate amount and Al is coated in an appropriate amount, the cycle performance of the material is the best, reaching 88.7%. Attached Figure Description

[0043] Figure 1 This is a SEM image of the modified cathode precursor prepared by the method described in Embodiment 1 of the present invention. Detailed Implementation

[0044] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0045] Example 1

[0046] This embodiment provides a modified cathode precursor, and the preparation method of the modified cathode precursor is as follows:

[0047] (1) Prepare a ternary solution (sulfate) with a molar ratio of Ni:Co:Mn = 0.6:0.1:0.3 and a concentration of 1.73 mol / L. Add zirconium sulfate to obtain a zirconium-doped ternary salt solution with a Zr concentration of 3.5 mmol / L.

[0048] (2) Prepare an aluminum sulfate solution with an aluminum concentration of 1.5 mol / L, a sodium hydroxide solution with a concentration of 8 mol / L, and an ammonia solution with a concentration of 4.7 mol / L. Control the flow rates of the zirconium-doped ternary salt solution, sodium hydroxide solution, and ammonia solution to be injected into the stirrer at 55 L / h, 18.2 L / h, and 5.1 L / h, respectively. The stirring speed is 260 rpm, the temperature is 68℃, and the pH is 10.6~11.6. Perform a one-step co-precipitation reaction until the particle size in the system reaches 3.3 μm.

[0049] (3) The injection rates of the precipitant and complexing agent are kept constant, the flow rate of the zirconium-doped ternary salt solution is adjusted to 33 L / h, the flow rate of the aluminum sulfate solution is 36 L / h, the reaction is carried out to the target particle size, and the mixture is washed with hot water and liquid alkali. The filter residue obtained by vacuum filtration and washing is dried in an oven at 160°C to finally obtain the modified cathode precursor.

[0050] The SEM image of the modified cathode precursor is as follows: Figure 1 As shown.

[0051] Example 2

[0052] This embodiment provides a modified cathode precursor, and the preparation method of the modified cathode precursor is as follows:

[0053] (1) Prepare a ternary solution (sulfate) with a molar ratio of Ni:Co:Mn = 0.5:0.2:0.3 and a concentration of 1.65 mol / L. Add zirconium sulfate to obtain a zirconium-doped ternary salt solution with a Zr concentration of 5.2 mmol / L.

[0054] (2) Prepare an aluminum sulfate solution with an aluminum concentration of 1.2 mol / L, a sodium hydroxide solution with a concentration of 7 mol / L, and an ammonia solution with a concentration of 4.5 mol / L. Control the flow rates of the zirconium-doped ternary salt solution, sodium hydroxide solution, and ammonia solution to be injected into the stirrer at 47 L / h, 15.3 L / h, and 4.2 L / h, respectively. The stirring speed is 320 rpm, the temperature is 50℃, and the pH is 10.2~11.2. Perform a one-step co-precipitation reaction until the particle size in the system reaches 3.2 μm.

[0055] (3) The injection rates of the precipitant and complexing agent are kept constant, the flow rate of the zirconium-doped ternary salt solution is adjusted to 23.5 L / h, the flow rate of the aluminum sulfate solution is 58.75 L / h, the reaction is carried out to the target particle size, and the mixture is washed with hot water and liquid alkali. The filter residue obtained by vacuum filtration and washing is dried in an oven at 160°C to finally obtain the modified cathode precursor.

[0056] Example 3

[0057] This embodiment provides a modified cathode precursor, and the preparation method of the modified cathode precursor is as follows:

[0058] (1) Prepare a ternary solution (sulfate) with a molar ratio of Ni:Co:Mn = 0.6:0.1:0.3 and a concentration of 1.75 mol / L. Add zirconium sulfate to obtain a zirconium-doped ternary salt solution with a Zr concentration of 7 mmol / L.

[0059] (2) Prepare an aluminum sulfate solution with an aluminum concentration of 1.5 mol / L, a sodium hydroxide solution with a concentration of 9 mol / L, and an ammonia solution with a concentration of 5 mol / L. Control the flow rates of the zirconium-doped ternary salt solution, sodium hydroxide solution, and ammonia solution to be injected into the stirrer at 38 L / h, 12.2 L / h, and 2.85 L / h, respectively. The stirring speed is 400 rpm, the temperature is 42℃, and the pH is 9.5~10.5. Perform a one-step co-precipitation reaction until the particle size in the system reaches 3.5 μm.

[0060] (3) The injection rates of the precipitant and complexing agent are kept constant, the flow rate of the zirconium-doped ternary salt solution is adjusted to 15.2 L / h, the flow rate of the aluminum sulfate solution is 57 L / h, the reaction is carried out to the target particle size, and the mixture is washed with hot water and liquid alkali. The filter residue obtained by vacuum filtration and washing is dried in an oven at 110°C to finally obtain the modified cathode precursor.

[0061] Example 4

[0062] The only difference between this embodiment and Example 1 is that the concentration of zirconium in the zirconium-doped ternary salt solution is 1 mmol / L. All other conditions and parameters are exactly the same as in Example 1.

[0063] Example 5

[0064] The only difference between this embodiment and Example 1 is that the concentration of zirconium in the zirconium-doped ternary salt solution is 10 mmol / L. All other conditions and parameters are exactly the same as in Example 1.

[0065] Example 6

[0066] The only difference between this embodiment and Example 1 is that the concentration of aluminum in the aluminum salt solution is 0.5 mol / L. All other conditions and parameters are exactly the same as in Example 1.

[0067] Example 7

[0068] The only difference between this embodiment and Example 1 is that the concentration of aluminum in the aluminum salt solution is 3 mol / L. All other conditions and parameters are exactly the same as in Example 1.

[0069] Comparative Example 1

[0070] The only difference between this comparative example and Example 1 is that aluminum and zirconium are mixed with the ternary salt solution at the same time; all other conditions and parameters are exactly the same as in Example 1.

[0071] Performance testing:

[0072] The precursors provided in the examples and comparative examples were mixed with lithium hydroxide at a molar ratio of Li:M (M is a metal element) = 1.05 and calcined in air at a temperature of 800°C for 13 hours to obtain the cathode material.

[0073] The positive electrode material provided in the examples and comparative examples is the positive electrode active material. The mass ratio of positive electrode active material:PVDF:SP is 95:3:2. NMP is added to obtain a positive electrode slurry, which is then coated onto the surface of aluminum foil to obtain a positive electrode sheet.

[0074] A coin cell is obtained by assembling a lithium sheet as the counter electrode with a positive electrode.

[0075] Electrochemical performance tests were conducted on the coin cells provided in the examples and comparisons. The test conditions were: electrochemical window: 2.5-4.3V, 100 cycles at 0.2C / 0.5C. The test results are shown in Table 1.

[0076] Table 1

[0077]

[0078]

[0079] As can be seen from Table 1, as obtained from Examples 1-3, the battery made from the modified cathode precursor of the present invention can achieve a capacity retention rate of over 85.1% after 100 cycles. When Zr doping is in an appropriate amount and Al coating is in an appropriate amount, the cycling performance of the material is the best, reaching 88.7%.

[0080] A comparison of Examples 1 and 4-5 shows that the concentration of zirconium in the zirconium-doped ternary salt solution affects the performance of the modified cathode precursor of the present invention. Controlling the concentration of zirconium in the zirconium-doped ternary salt solution to 2-8 mmol / L results in a precursor with better performance. If the zirconium concentration is too high, there will be too many Zr atoms in the material, causing material deformation and affecting the material's cycle stability. If the zirconium concentration is too low, it will not play a supporting role in the material.

[0081] A comparison of Examples 1 and 5-6 shows that the concentration of aluminum in the aluminum salt solution affects the performance of the modified cathode precursor of the present invention. Controlling the concentration of aluminum in the aluminum salt solution to 1-2 mmol / L results in a precursor with better performance. If the aluminum concentration is too high, the amount of aluminum coating will be too large, reducing the overall relative capacity of the material. The alumina formed after sintering will hinder electron transport. If the aluminum concentration is too low, the alumina coating effect will not be achieved, and the side reactions between the electrolyte and the material will not be prevented.

[0082] As can be seen from the comparison between Example 1 and Comparative Example 1, the present invention pre-mixes the nickel-cobalt-manganese ternary salt solution with zirconium salt and feeds them simultaneously, while feeding Al raw material separately. This reduces redundant processes and lowers costs, while effectively stabilizing the uniformity of Zr and Al elements in nickel-cobalt-manganese, thereby producing a high-performance cathode precursor.

[0083] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing an internally doped and externally coated modified cathode precursor, characterized in that, The preparation method includes the following steps: (1) Mix the nickel-cobalt-manganese ternary salt solution with zirconium salt to obtain a zirconium-doped ternary salt solution; (2) A one-step co-precipitation reaction was carried out by injecting zirconium-doped ternary salt solution, precipitant and complexing agent into the bottom liquid in a co-flow manner; (3) The injection rates of the precipitant and complexing agent remain unchanged, the injection rate of the zirconium-doped ternary salt solution is reduced, and the aluminum salt solution is injected in parallel to carry out a two-step co-precipitation reaction to obtain the modified cathode precursor. In step (1), the elemental molar ratio of nickel, cobalt, and manganese in the nickel-cobalt-manganese ternary salt solution is Ni:Co:Mn=x:y:0.3, 0.5≤x<0.7, 0 <y≤0.2,0.3+x+y=1; The concentration of zirconium in the zirconium-doped ternary salt solution in step (1) is 3~7 mmol / L; The flow rate of the zirconium-doped ternary salt solution in step (2) is 38~60 L / h; The endpoint of the one-step coprecipitation reaction described in step (2) is when the particle size in the system is 3~4μm; The flow rate of the zirconium-doped ternary salt solution in step (3) is 15~35 L / h; The concentration of aluminum in the aluminum-containing salt solution is 1~2 mol / L; The flow rate of the aluminum salt solution is 30~60 L / h.

2. The preparation method according to claim 1, characterized in that, The total concentration of metal ions in the nickel-cobalt-manganese ternary salt solution is 1.5~2 mol / L.

3. The preparation method according to claim 1, characterized in that, The precipitant in step (2) includes sodium hydroxide solution and / or potassium hydroxide solution.

4. The preparation method according to claim 1, characterized in that, The concentration of the precipitant is 7~9 mol / L.

5. The preparation method according to claim 1, characterized in that, The complexing agent includes ammonia.

6. The preparation method according to claim 1, characterized in that, The concentration of the complexing agent is 4.5~5 mol / L.

7. The preparation method according to claim 1, characterized in that, The flow rate of the precipitant is 10~20 L / h.

8. The preparation method according to claim 1, characterized in that, The flow rate of the complexing agent is 2.5~5.5 L / h.

9. The preparation method according to claim 1, characterized in that, The temperature of the one-step coprecipitation reaction in step (2) is 40~70℃.

10. The preparation method according to claim 1, characterized in that, The stirring speed for the one-step coprecipitation reaction in step (2) is 250~400 rpm.

11. The preparation method according to claim 1, characterized in that, The pH of the one-step coprecipitation reaction in step (2) is 9.5~12.

12. The preparation method according to claim 1, characterized in that, The solute in the aluminum-containing salt solution includes any one or a combination of at least two of sodium aluminate, aluminum sulfate, or aluminum nitrate.

13. The preparation method according to claim 1, characterized in that, The temperature of the two-step coprecipitation reaction in step (3) is 40~70℃.

14. The preparation method according to claim 1, characterized in that, The stirring speed for the two-step coprecipitation reaction in step (3) is 250~400 rpm.

15. The preparation method according to claim 1, characterized in that, The pH of the two-step coprecipitation reaction in step (3) is 9.5~12.

16. The preparation method according to claim 1, characterized in that, After the two-step coprecipitation reaction described in step (3), the product is washed and dried.

17. The preparation method according to claim 16, characterized in that, The detergent used for washing includes hot water and liquid alkali.

18. A modified positive electrode precursor, characterized in that, The modified cathode precursor is prepared by the method described in any one of claims 1-17.

19. A positive electrode material, characterized in that, The cathode material is prepared by sintering the modified cathode precursor as described in claim 18 with a lithium source.

20. A lithium-ion battery, characterized in that, The lithium-ion battery comprises the positive electrode material as described in claim 19.

Images