Modified lithium-rich manganese-based precursor as well as preparation method therefor and use thereof

Abstract

A modified lithium-rich manganese-based precursor as well as a preparation method therefor and the use thereof. The preparation method comprises the following steps: (1) adding a nickel-manganese binary salt solution, a precipitant and a complexing agent to a reaction apparatus containing a base solution, and carrying out first-step coprecipitation reaction to obtain a nickel-manganese binary precursor; and (2) adding a cobalt salt solution and an organic complexing carbon source solution to a reaction apparatus in a parallel flow manner, and carrying out second-step coprecipitation reaction to obtain the modified lithium-rich manganese-based precursor. The modified lithium-rich manganese-based precursor has a stable structure and good rate capacity, and positive electrode materials prepared from same have excellent capacity performance and cycle performance.

Description

A modified lithium-rich manganese-based precursor and its preparation method and application Technical Field

[0001] The present application relates to the field of lithium-ion battery technology, for example, a modified lithium-rich manganese-based precursor and its preparation method and application. Background Art

[0002] In recent years, the application areas of lithium-ion batteries have continued to expand, from traditional 3C products to current electric vehicles and smart grids. The new energy industry has an increasingly urgent demand for lithium-ion batteries, especially high-energy-density lithium batteries. To meet this demand, a large amount of research has been devoted to the development of electrode materials with high specific capacity. The lithium-rich manganese-based cathode material xLi2MnO3·(1-x)LiMO2 (M=one or more of Ni, Co, Mn, Al, V, Cr, Fe) has a discharge capacity exceeding 250mAh / g and an operating voltage greater than 3.50V. Due to its high specific capacity, good thermal stability, excellent cycle performance, wide charge and discharge voltage range, low price, and environmental friendliness, it has attracted in-depth research from many experts and scholars in the industry and has great development potential.

[0003] Although lithium-rich manganese-based positive electrode materials have a high specific capacity of more than 250 mAh / g, there are still many problems in their application in actual production, including low initial efficiency (about 75%) and obvious voltage and capacity decay during the cycle.

[0004] CN106564967A discloses a lithium-rich manganese-based cathode material precursor, cathode material, and preparation method thereof. In this method, metal salts (i.e., manganese salt, cobalt salt, and nickel salt) and a surfactant are mixed and dissolved in water to obtain a metal salt solution; a precipitant is dissolved in water and stirred to obtain a precipitant solution; the metal salt solution and the precipitant solution undergo a liquid-liquid coprecipitation reaction in a high-gravity field reactor, followed by filtration, washing, and vacuum drying to obtain the precursor.

[0005] CN112158893A discloses a method for preparing a lithium-rich manganese-based positive electrode material precursor, comprising: preparing a mixed salt solution A of nickel and manganese, and a mixed salt solution B of nickel, cobalt and manganese, introducing an inert gas into a reactor containing a base liquid, adding the mixed salt solution A, ammonia water and an alkaline solution to the reactor respectively and stirring, adding the mixed salt solution B, ammonia water and an alkaline solution, and reacting to obtain a precursor with a particle size between 13μm and 18μm.

[0006] The coating layer of the precursor prepared by the method described in the above scheme will result in poor rate performance of the material, obvious cracking will occur after cycling, and the application prospect is poor.

[0007] Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] The present application provides a modified lithium-rich manganese-based precursor and its preparation method and application. The modified lithium-rich manganese-based precursor described in the present application has a stable structure and good rate performance, and the prepared positive electrode material has excellent capacity performance and cycle performance.

[0010] In a first aspect, the present application provides a method for preparing a modified lithium-rich manganese-based precursor, the preparation method comprising the following steps:

[0011] (1) adding a nickel-manganese binary salt solution, a precipitant, and a complexing agent concurrently into a reaction device containing a base liquid, and obtaining a nickel-manganese binary precursor through a one-step coprecipitation reaction;

[0012] (2) The cobalt salt solution and the organic complex carbon source solution are added to the reaction device in parallel, and the modified lithium-rich manganese-based precursor is obtained through a two-step coprecipitation reaction.

[0013] This application achieves cobalt-complexed organic carbon coating through two-step co-precipitation, which not only isolates the lithium-rich manganese core from the electrolyte to improve the battery's initial efficiency and cycle performance, but also cobalt is an active substance and organic carbon can improve the conductivity of the positive electrode material, thereby increasing the capacity of the material.

[0014] In one embodiment, the mass concentration of the nickel-manganese binary salt solution in step (1) is 80-120 g / L, for example, 8 g / L, 9 g / L, 10 g / L, 11 g / L or 12 g / L.

[0015] In one embodiment, the molar ratio of nickel to manganese in the nickel-manganese binary salt solution is (2-4):(6-8), for example: 2:8, 2.5:7.5, 3:7, 3.5:6.5 or 4:6.

[0016] In one embodiment, the precipitating agent comprises an alkali solution.

[0017] In one embodiment, the mass concentration of the precipitant is 28-32%, for example, 28%, 29%, 30%, 31% or 32%.

[0018] In one embodiment, the complexing agent comprises aqueous ammonia.

[0019] In one embodiment, the mass concentration of the complexing agent is 10-20%, for example, 10%, 12%, 15%, 18% or 20%.

[0020] In one embodiment, the concentration of aqueous ammonia in the base solution is 4 to 8 g / L, for example, 4 g / L, 5 g / L, 6 g / L, 7 g / L or 8 g / L.

[0021] In one embodiment, the temperature of the base liquid is 40-60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C.

[0022] In one embodiment, the pH of the base solution is 11-12, for example, 11, 11.2, 11.5, 11.8 or 12.

[0023] In one embodiment, the flow rate of the nickel-manganese binary salt solution in step (1) is 6 to 10 L / h, for example, 6 L / h, 7 L / h, 8 L / h, 9 L / h or 10 L / h.

[0024] In one embodiment, the flow rate of the precipitant is 2 to 3 L / h, for example, 2 L / h, 2.2 L / h, 2.5 L / h, 2.8 L / h or 3 L / h.

[0025] In one embodiment, the flow rate of the complexing agent is 0.3 to 0.6 L / h, for example, 0.3 L / h, 0.35 L / h, 0.4 L / h, 0.5 L / h or 0.6 L / h.

[0026] In one embodiment, the concentration of aqueous ammonia in the one-step coprecipitation reaction in step (1) is 4 to 8 g / L, for example, 4 g / L, 5 g / L, 6 g / L, 7 g / L or 8 g / L.

[0027] In one embodiment, the temperature of the one-step coprecipitation reaction is 40-60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C.

[0028] In one embodiment, the pH of the one-step coprecipitation reaction is 10-12, for example, 10, 10.5, 11, 11.5 or 12.

[0029] In one embodiment, the stirring speed of the one-step coprecipitation reaction is 200-400 rpm, for example, 200 rpm, 250 rpm, 300 rpm, 350 rpm or 400 rpm.

[0030] In one embodiment, the median particle size D50 of the particles in the one-step coprecipitation reaction system is 3 to 4 μm (eg, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, or 4 μm, etc.) and the feeding is stopped.

[0031] In one embodiment, the nickel-manganese binary precursor in step (1) is centrifuged and washed before being put back into the reaction device.

[0032] In one embodiment, the mass concentration of the cobalt salt solution in step (2) is 80-120 g / L, for example, 8 g / L, 9 g / L, 10 g / L, 11 g / L or 12 g / L.

[0033] In one embodiment, the organic complex carbon source includes any one or a combination of at least two of citric acid, oxalic acid, sucrose, glucose, fructose or ascorbic acid.

[0034] In one embodiment, the mass concentration of the organic complex carbon source solution is 10-20%, for example, 10%, 12%, 15%, 18% or 20%.

[0035] In one embodiment, the mass of the cobalt element in the cobalt source is 2-3% of the total mass of nickel and manganese in the nickel-manganese binary precursor.

[0036] In one embodiment, the molar ratio of the cobalt element in the cobalt source to the organic complex carbon source is 2:(0.5-1), for example, 2:0.5, 2:0.6, 2:0.8, 2:0.9 or 2:1.

[0037] The ratio of the cobalt source and the organic complex carbon source described in this application depends on the type of carbon source, mainly satisfying that all the carbon source is complexed with cobalt, there is excess cobalt, the complex obtained by the complexation of the carbon source and cobalt is coated on the surface of the precursor, and the excess cobalt ions are free in the solution.

[0038] In one embodiment, the flow rate of the cobalt salt solution in step (2) is 6 to 10 L / h, for example, 6 L / h, 7 L / h, 8 L / h, 9 L / h or 10 L / h.

[0039] In one embodiment, the flow rate of the organic complex carbon source solution is 0.3 to 0.6 L / h, for example, 0.3 L / h, 0.35 L / h, 0.4 L / h, 0.5 L / h or 0.6 L / h.

[0040] In one embodiment, the stirring speed of the two-step co-precipitation reaction is 200-400 rpm, for example, 200 rpm, 250 rpm, 300 rpm, 350 rpm or 400 rpm.

[0041] In a second aspect, the present application provides a modified lithium-rich manganese-based precursor, which is prepared by the method described in the first aspect.

[0042] In a third aspect, the present application provides a modified lithium-rich manganese-based positive electrode material, which is obtained by mixing and sintering the modified lithium-rich manganese-based precursor described in the second aspect with a lithium source.

[0043] In a fourth aspect, the present application provides a lithium-ion battery, which comprises the modified lithium-rich manganese-based positive electrode material as described in the third aspect.

[0044] Compared with the related art, this application has the following beneficial effects:

[0045] (1) The present application coats a complex of cobalt and organic carbon material on the surface of the precursor. Coating cobalt and carbon source helps to improve the rupture of the positive electrode during cycling. Secondly, cobalt is an active substance and carbon source is a good conductive material. Both of these help to improve the capacity of the material.

[0046] (2) The 0.5C discharge specific capacity of the battery made from the modified lithium-rich manganese-based precursor described in this application can reach more than 246.13 mAh / g, and the capacity retention rate after 600 cycles can reach more than 94.23%.

[0047] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0049] FIG1 is a SEM image of the modified lithium-rich manganese-based precursor described in Example 1 of the present application.

[0050] FIG2 is a distribution diagram of cobalt in the modified lithium-rich manganese-based precursor described in Example 1 of the present application. DETAILED DESCRIPTION

[0051] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0052] Unless otherwise specified, the concentrations described in the examples and comparative examples of the present application are by mass concentrations.

[0053] Example 1

[0054] This embodiment provides a modified lithium-rich manganese-based precursor. The preparation method of the modified lithium-rich manganese-based precursor is as follows:

[0055] (1) A nickel-manganese disulfuric acid solution (Ni:Mn=4:6) with a mass concentration of 100 g / L, 30% alkali solution and 15% ammonia water were added to a reaction device containing a bottom liquid (ammonia concentration of 6 g / L, 50°C, pH of 11.5) at flow rates of 8 L / h, 2.5 L / h and 0.5 L / h, respectively. A one-step coprecipitation reaction was carried out under nitrogen protection and stirring at 300 rpm. The ammonia concentration of the reaction was controlled to be 6 g / L, 50°C and pH of 11. The particle size was continuously monitored. Before the particle size reached the requirement, a high-efficiency concentrator was used in the reaction process to collect all the particles and return them to the reactor for continuous reaction growth. When the particle size D 50 When the particle size reaches 3.5 μm, the feeding is stopped and the reaction is continued until the material reaction is complete to obtain a nickel-manganese binary precursor;

[0056] (2) The nickel-manganese binary precursor is centrifuged, washed, and then put back into the reactor. A cobalt sulfate solution with a concentration of 100 g / L and citric acid with a mass concentration of 15% are simultaneously added to the reactor at feed rates of 8 L / h and 0.5 L / h, respectively. A coprecipitation reaction is carried out at a stirring rate of 300 rpm. The amount of cobalt added is 2.5 wt% of the nickel-manganese, and the molar ratio of cobalt to citric acid is 2:0.8, thereby obtaining the modified lithium-rich manganese-based precursor.

[0057] The SEM image of the modified lithium-rich manganese-based precursor is shown in Figure 1, and the distribution diagram of cobalt in the modified lithium-rich manganese-based precursor is shown in Figure 2. It can be seen from Figure 2 that the cobalt in the precursor described in this application is evenly distributed on the surface of the precursor.

[0058] Example 2

[0059] This embodiment provides a modified lithium-rich manganese-based precursor. The preparation method of the modified lithium-rich manganese-based precursor is as follows:

[0060] (1) A nickel-manganese disulfuric acid solution (Ni:Mn=3:7) with a mass concentration of 80 g / L, 28% alkali solution and 10% ammonia water were added to a reaction device containing a bottom liquid (ammonia concentration of 4 g / L, 40°C, pH of 11) at flow rates of 6 L / h, 2 L / h and 0.3 L / h, respectively. A one-step coprecipitation reaction was carried out under nitrogen protection and stirring at 200 rpm. The ammonia concentration of the reaction was controlled to be 4 g / L, 40°C and pH of 10. The particle size was continuously monitored. Before the particle size reached the required value, a high-efficiency concentrator was used in the reaction process to collect all the particles and return them to the reactor for continuous reaction growth. When the particle size D 50 When the particle size reaches 3 μm, the feeding is stopped and the reaction is continued until the reaction is complete to obtain a nickel-manganese binary precursor.

[0061] (2) The nickel-manganese binary precursor is centrifuged, washed, and then put back into the reactor. A cobalt sulfate solution with a concentration of 80 g / L and oxalic acid with a mass concentration of 10% are simultaneously added to the reactor at feed rates of 6 L / h and 0.3 L / h, respectively. A coprecipitation reaction is carried out at a stirring rate of 200 rpm. The amount of cobalt added is 2 wt% of the nickel-manganese, and the molar ratio of cobalt to oxalic acid is 2:1, thereby obtaining the modified lithium-rich manganese-based precursor.

[0062] Example 3

[0063] This embodiment provides a modified lithium-rich manganese-based precursor. The preparation method of the modified lithium-rich manganese-based precursor is as follows:

[0064] (1) A nickel-manganese disulfuric acid solution (Ni:Mn=2:8) with a mass concentration of 80 g / L, 32% alkali solution and 10% ammonia water were added to a reaction device containing a bottom liquid (ammonia concentration of 8 g / L, 60°C, pH of 12) at flow rates of 10 L / h, 3 L / h and 0.6 L / h, respectively. A one-step coprecipitation reaction was carried out under nitrogen protection and stirring at 400 rpm. The ammonia concentration of the reaction was controlled to be 8 g / L, 60°C and pH of 12. The particle size was continuously monitored. Before the particle size reached the requirement, a high-efficiency concentrator was used in the reaction process to collect all the particles and return them to the reactor for continuous reaction growth. When the particle size D 50 When the particle size reaches 4 μm, the feeding is stopped and the reaction is continued until the material reaction is complete to obtain a nickel-manganese binary precursor;

[0065] (2) The nickel-manganese binary precursor is centrifuged, washed, and then put back into the reactor. A cobalt sulfate solution with a concentration of 120 g / L and glucose with a mass concentration of 20% are simultaneously added to the reactor at feed rates of 10 L / h and 0.6 L / h, respectively. A coprecipitation reaction is carried out at a stirring rate of 400 rpm. The amount of cobalt added is 3 wt% of the nickel-manganese, and the molar ratio of cobalt to glucose is 2:0.5, thereby obtaining the modified lithium-rich manganese-based precursor.

[0066] Example 4

[0067] The only difference between this embodiment and embodiment 1 is that the amount of cobalt added is 1.5 wt % of the nickel and manganese. Other conditions and parameters are exactly the same as those in embodiment 1.

[0068] Example 5

[0069] The only difference between this embodiment and embodiment 1 is that the amount of cobalt added is 3.5 wt % of the nickel and manganese. Other conditions and parameters are exactly the same as those in embodiment 1.

[0070] Example 6

[0071] The only difference between this embodiment and embodiment 1 is that the molar ratio of cobalt to citric acid is 1:1, and other conditions and parameters are exactly the same as those in embodiment 1.

[0072] Comparative Example 1

[0073] The only difference between this comparative example and Example 1 is that no cobalt salt solution is added, and other conditions and parameters are exactly the same as those in Example 1.

[0074] Comparative Example 2

[0075] The only difference between this comparative example and Example 1 is that citric acid is replaced by urea, and the other conditions and parameters are exactly the same as those in Example 1.

[0076] Performance testing:

[0077] The positive electrode material precursor obtained in the embodiment and the comparative example was evenly mixed with lithium hydroxide in a mortar at a ratio of 1:1.05, and calcined at 850°C for 20 hours to obtain a positive electrode material. The positive electrode material was used to prepare a positive electrode sheet, and a button battery was prepared using a lithium sheet as a counter electrode. The obtained button battery was tested for cycle performance and rate performance.

[0078] The battery performance test system (model: BTS05 / 10C8D-HP) of Shenghong Electric Co., Ltd. was used to test the cycle capacity retention rate: at 25°C, the battery was cycled at a charge and discharge rate of 0.5C. After 600 cycles, the discharge capacity of the battery at this time was divided by the discharge capacity of the first cycle, which is the battery's 600-cycle capacity retention rate. The test results are shown in Table 1:

[0079] Table 1

[0080] As can be seen from Table 1, from Examples 1-3, the 0.5C discharge specific capacity of the battery made from the modified lithium-rich manganese-based precursor described in this application can reach more than 246.13 mAh / g, and the capacity retention rate after 600 cycles can reach more than 94.23%.

[0081] By comparing Example 1 with Examples 4-5, it can be seen that during the preparation process of the modified lithium-rich manganese-based precursor described in the present application, the amount of cobalt source added will affect its performance. The mass of the cobalt element in the cobalt source is controlled at 2-3% of the total mass of nickel and manganese in the nickel-manganese binary precursor to obtain a precursor with better performance. If the amount of cobalt source added is too high, the cost is too high, and it will not have a significant effect on the performance of the material. If the amount of cobalt source added is too low, the coating effect will not be achieved and the cycle performance will be very poor.

[0082] By comparing Example 1 and Example 6, it can be seen that during the preparation process of the modified lithium-rich manganese-based precursor described in the present application, the addition ratio of the cobalt source and the organic complex carbon source will affect its performance. According to the complexation equation, the excess cobalt is controlled. If the amount of carbon source added is too large (there is still a residue after complexing with cobalt), it will instead affect the subsequent washing and sintering, and affect the capacity of the material.

[0083] By comparing Example 1 and Comparative Examples 1-2, it can be seen that in the present application, a cobalt salt and an organic carbon source that can complex with the cobalt salt are added in the two-step co-precipitation, and the two undergo a complex reaction. The generated complex is evenly coated on the surface of the precursor core, which not only isolates the lithium-rich manganese core from the electrolyte and thus improves the initial efficiency and cycle performance of the battery, but also cobalt is an active substance and organic carbon can improve the conductivity of the positive electrode material, thereby increasing the capacity of the material.

[0084] The applicant declares that the above is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Technical personnel in the relevant technical field should understand that any changes or substitutions that can be easily thought of by technical personnel in the relevant technical field within the technical scope disclosed in this application fall within the protection scope and disclosure scope of this application.

Claims

1. A method for preparing a modified lithium-rich manganese-based precursor, comprising the following steps: (1) adding a nickel-manganese binary salt solution, a precipitant, and a complexing agent in parallel to a reaction device containing a base liquid to obtain a nickel-manganese binary precursor through a one-step coprecipitation reaction; (2) Adding the cobalt salt solution and the organic complex carbon source solution into a reaction device in parallel, and performing a two-step coprecipitation reaction to obtain the modified lithium-rich manganese-based precursor.

2. The preparation method according to claim 1, wherein The mass concentration of the nickel-manganese binary salt solution in step (1) is 80-120 g / L.

3. The preparation method according to claim 1 or 2, wherein: The molar ratio of nickel to manganese in the nickel-manganese binary salt solution is (2-4):(6-8).

4. The preparation method according to any one of claims 1 to 3, wherein The precipitating agent includes alkali solution.

5. The preparation method according to any one of claims 1 to 4, wherein: The mass concentration of the precipitant is 28-32%.

6. The preparation method according to any one of claims 1 to 5, wherein: The complexing agent includes ammonia; Optionally, the mass concentration of the complexing agent is 10-20%.

7. The preparation method according to any one of claims 1 to 6, wherein: The concentration of ammonia water in the base liquid is 4 to 8 g / L; Optionally, the temperature of the base liquid is 40-60°C; Optionally, the pH of the base solution is 11-12.

8. The preparation method according to any one of claims 1 to 7, wherein: The flow rate of the nickel-manganese binary salt solution in step (1) is 6 to 10 L / h; Optionally, the flow rate of the precipitant is 2 to 3 L / h; Optionally, the flow rate of the complexing agent is 0.3 to 0.6 L / h.

9. The preparation method according to any one of claims 1 to 8, wherein: The concentration of aqueous ammonia in the one-step coprecipitation reaction of step (1) is 4 to 8 g / L; Optionally, the temperature of the one-step coprecipitation reaction is 40 to 60° C.; Optionally, the pH of the one-step coprecipitation reaction is 10 to 12; Optionally, the stirring speed of the one-step coprecipitation reaction is 200 to 400 rpm; Optionally, the feeding is stopped when the median particle size D50 of the particles in the one-step coprecipitation reaction system is 3 to 4 μm.

10. The preparation method according to any one of claims 1 to 9, wherein: The nickel-manganese binary precursor in step (1) is centrifuged and washed and then put back into the reaction device.

11. The preparation method according to any one of claims 1 to 10, wherein: The mass concentration of the cobalt salt solution in step (2) is 80-120 g / L; Optionally, the organic complex carbon source includes any one or a combination of at least two of citric acid, oxalic acid, sucrose, glucose, fructose or ascorbic acid; Optionally, the mass concentration of the organic complex carbon source solution is 10-20%; Optionally, the mass of the cobalt element in the cobalt source is 2-3% of the total mass of nickel and manganese in the nickel-manganese binary precursor; Optionally, the molar ratio of the cobalt element in the cobalt source to the organic complex carbon source is 2:(0.5-1).

12. The preparation method according to any one of claims 1 to 11, wherein: The flow rate of the cobalt salt solution in step (2) is 6 to 10 L / h; Optionally, the flow rate of the organic complex carbon source solution is 0.3 to 0.6 L / h; Optionally, the stirring speed of the two-step coprecipitation reaction is 200-400 rpm.

13. A modified lithium-rich manganese-based precursor, wherein: The modified lithium-rich manganese-based precursor is prepared by the method according to any one of claims 1 to 12.

14. A modified lithium-rich manganese-based positive electrode material, wherein: The modified lithium-rich manganese-based material is obtained by mixing and sintering the modified lithium-rich manganese-based precursor described in claim 13 with a lithium source.

15. A lithium ion battery, wherein: The lithium-ion battery comprises the modified lithium-rich manganese-based positive electrode material as claimed in claim 14.

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