Lithium-rich manganese-based positive electrode material, and preparation method therefor and use thereof

Abstract

A lithium-rich manganese-based positive electrode material, and a preparation method therefor and the use thereof. The preparation method comprises the following steps: (1) pre-sintering a lithium-rich manganese-based precursor to obtain an oxide precursor; and (2) mixing the oxide precursor with a lithium source, and roasting same to obtain the lithium-rich manganese-based positive electrode material, wherein the molar ratio (TM / Li) of the total molar weight of metal elements in the oxide precursor to lithium in the lithium source is 1:(1.2-1.4). By means of a simple one-step three-in-one surface treatment technique, a coating with lithium vacancies, a spinel phase and nickel doping is synchronously constructed on a surface of the lithium-rich manganese-based positive electrode material, thereby allowing the lithium-rich manganese-based positive electrode material to have high rate performance, inhibited voltage attenuation and good long-term cycling stability at the same time.

Description

A lithium-rich manganese-based positive electrode material and its preparation method and application Technical Field

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

[0002] The rise of electric vehicles around the world has prompted a widespread search for low-cost, high-energy-density, next-generation rechargeable batteries. One of the main bottlenecks in commercial lithium-ion batteries (LIBs) is the low cathode capacity. Lithium-rich manganese-based layered oxides (LLOs) with reversible capacities exceeding 250 mAh / g are considered candidate cathode materials for low-cost, high-energy-density LIBs. The extraordinary capacity of LLOs is primarily attributed to anionic redox reactions under high voltage, including a large number of reversible anionic redox processes (O 2- →O 2n- ) and irreversible O2 released mainly on the surface. Irreversible O2 release simultaneously brings about structural evolution and particle cracking, resulting in several fatal disadvantages, such as poor rate capability and severe voltage and capacity decay. Due to the high operating voltage, LLO also undergoes undesirable cathode-electrolyte interface reactions, leading to electrolyte decomposition, transition metal (TM) ion migration, surface corrosion and cathode dissolution. This further exacerbates the decay in rate capability and cycle life. All of the above problems have seriously hindered the large-scale application of LLO in electric vehicles.

[0003] Lithium ions are a prerequisite for high specific capacity to utilize the additional anionic redox in LLO. However, excess lithium ions in the lattice are kinetically unfavorable. However, higher lithium utilization leads to a deeper delithiation state of LLO, resulting in capacity fade, voltage fade and poor kinetics. The spinel phase can act as a protective layer to suppress surface lattice oxygen release and improve the problems of capacity fade and voltage fade. In-situ nickel doping can improve the stability of the crystal structure, however nickel doping may hinder the migration of Li+ and lead to poor rate performance.

[0004] CN113788500A discloses a surface modification method for a lithium-rich manganese-based cathode material and a lithium-rich manganese-based cathode material. The surface modification method comprises uniformly mixing the lithium-rich manganese-based cathode material with a stannous salt solution, reacting the mixture at a constant temperature of 50-95°C for 2 minutes to 20 hours under stirring, filtering the reaction product, washing and drying the filtered solid, and sintering the mixture at 300-800°C for 30 minutes to 4 hours to obtain a surface-modified lithium-rich manganese-based cathode material.

[0005] CN111640931A discloses a method for preparing a lithium-rich manganese-based positive electrode material, comprising the following steps: S1, preparing a magnesium-doped precursor by a carbonate co-precipitation method: dissolving nickel salt, manganese salt and magnesium salt in water to obtain a mixed metal salt solution, and injecting the mixed metal salt solution and a precipitant solution into a reactor respectively, adjusting the pH value by a complexing agent, reacting for 24-120 hours to generate a precipitate, and washing, drying, crushing and sieving the precipitate to obtain a precursor; S2, mixing the precursor with a lithium source and calcining: after fully grinding and mixing the precursor and the lithium source, sintering to obtain the positive electrode material.

[0006] The above scheme obtains lithium-rich manganese-based positive electrode materials by modifying the lithium-rich manganese-based positive electrode materials by doping. Although doping can effectively improve capacity decay, voltage decay or rate performance, they can only suppress one of the destructive challenges and have no synergistic effect on each other.

[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 lithium-rich manganese-based positive electrode material, a preparation method and an application thereof. The present application utilizes a simple one-step three-in-one surface treatment technology to simultaneously construct lithium vacancies, a spinel phase and a nickel-doped coating on the surface of the lithium-rich manganese-based positive electrode material, so that the lithium-rich manganese-based positive electrode material has high rate performance, suppressed voltage decay and excellent long-term cycle stability.

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

[0011] (1) pre-calcining a lithium-rich manganese-based precursor to obtain an oxide precursor;

[0012] (2) mixing the oxide precursor and a lithium source, and calcining the mixture to obtain the lithium-rich manganese-based positive electrode material;

[0013] Wherein, the molar ratio (TM / Li) of the total molar amount of the metal elements in the oxide precursor to the lithium element in the lithium source is 1:(1.2-1.4).

[0014] This application uses a simple one-step three-in-one surface treatment technology to simultaneously construct lithium vacancies, spinel phases and nickel-doped coatings on the surface of lithium-rich manganese-based positive electrode materials. Lithium vacancies have a larger diffusion coefficient and lower cost (Li / TM≥1.5 in conventional lithium-rich manganese-based positive electrode materials). The lack of lithium can induce the formation of spinel in a timely manner. In addition, under lithium-deficient conditions, nickel ions tend to migrate to the lithium plate because the energy barrier of nickel ions is the lowest among all transition metal (Mn, Co, Ni) ions in LLO. The nickel ions in the lithium plate can be used as doping elements to improve the stability of the crystal structure. In addition, the obstacles of nickel ions in Li+ migration can be compensated by intentionally pre-introduced lithium vacancies. Therefore, this application introduces lithium vacancies to induce the formation of spinel phases on the crystal surface and in-situ nickel doping, thereby improving the rate performance of dynamic LLO, and the idea of ​​suppressing capacity and voltage decay is expected to become a reality. In addition, nickel doping can stabilize the crystal structure, and the in-situ spinel coating due to lithium deficiency can protect the positive electrode material from electrolyte erosion and suppress the release of surface lattice oxygen. The method described in this application is simple, low-cost, and highly repeatable, and is very suitable for large-scale production.

[0015] In one embodiment, the chemical formula of the lithium-rich manganese-based precursor in step (1) is Ni x Co y Mn 1-x-y (OH)2, wherein 0.4≥x>0.3, y<0.1.

[0016] In one embodiment, the temperature of the pre-calcination treatment in step (1) is 300-600°C, for example, 300°C, 350°C, 400°C, 500°C or 600°C.

[0017] In one embodiment, the pre-firing treatment time is 3 to 7 hours, for example, 3 hours, 4 hours, 5 hours, 6 hours or 7 hours.

[0018] In one embodiment, the lithium source in step (2) includes lithium carbonate and / or lithium hydroxide.

[0019] In one embodiment, the calcination temperature in step (2) is 800-1000°C, for example, 800°C, 850°C, 900°C, 950°C or 1000°C.

[0020] In one embodiment, the calcination treatment time is 10 to 14 hours, for example, 10 hours, 11 hours, 12 hours, 13 hours or 14 hours.

[0021] In a second aspect, the present application provides a lithium-rich manganese-based positive electrode material, which is prepared by the method described in the first aspect.

[0022] In one embodiment, the lithium-rich manganese-based positive electrode material includes a lithium-rich manganese-based core and a composite coating layer disposed on the surface of the lithium-rich manganese-based core.

[0023] In one embodiment, the composite coating layer contains lithium vacancies, a spinel phase, and a nickel-doped coating.

[0024] The surface of the lithium-rich manganese-based cathode material described herein contains lithium vacancies, a spinel phase, and a nickel-doped coating. Lithium vacancies have a greater diffusion coefficient and lower cost, nickel doping stabilizes the crystal structure, and the in-situ spinel coating, created due to lithium deficiency, protects the cathode material from electrolyte corrosion and inhibits the release of surface lattice oxygen. This lithium-rich manganese-based cathode material exhibits high rate performance, suppressed voltage decay, and excellent long-term cycling stability.

[0025] In a third aspect, the present application provides a positive electrode plate, which comprises the lithium-rich manganese-based positive electrode material as described in the second aspect.

[0026] In a fourth aspect, the present application provides a lithium-ion battery, wherein the lithium-ion battery comprises the positive electrode sheet as described in the third aspect.

[0027] Compared with the related art, this application has the following beneficial effects:

[0028] (1) This application utilizes a simple one-step three-in-one surface treatment technology to simultaneously construct lithium vacancies, spinel phases, and nickel-doped coatings on the surface of lithium-rich manganese-based cathode materials. Lithium vacancies have a larger diffusion coefficient and lower cost, nickel doping can stabilize the crystal structure, and the in-situ spinel coating due to lithium deficiency can protect the cathode material from electrolyte corrosion and inhibit the release of surface lattice oxygen. The lithium-rich manganese-based cathode material has high rate performance, suppressed voltage decay, and excellent long-term cycle stability.

[0029] (2) The discharge capacity of the battery made of the lithium-rich manganese-based positive electrode material described in this application can reach more than 245.53mAh / g, the capacity retention rate after 50 weeks is more than 95.2%, and the capacity retention rate after 100 weeks is more than 87.83% (by appropriately adjusting the type of precursor, the discharge capacity can reach a maximum of 273.93mAh / g, the capacity retention rate after 50 weeks is 99.57%, and the capacity retention rate after 100 weeks is 98.24%). The lithium-rich manganese-based positive electrode with lithium defects also exhibits good rate performance, further illustrating that the simple one-step three-in-one surface treatment technology used in this application helps to improve the performance of the lithium-rich manganese-based positive electrode.

[0030] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] 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.

[0032] FIG1 is an XRD comparison diagram of Examples 1-2, Comparative Example 1 and Comparative Example 3 of the present application.

[0033] FIG2 is an XRD enlarged comparison diagram of Examples 1-2, Comparative Example 1 and Comparative Example 3 of the present application.

[0034] FIG3 is a comparison chart of the rate performance of Examples 1-2, Comparative Example 1, and Comparative Example 3 of the present application.

[0035] FIG4 is a comparison chart of the capacity performance of Examples 1-2, Comparative Example 1, and Comparative Example 3 of the present application.

[0036] FIG5 is a comparison chart of the cycle performance of Examples 1-2, Comparative Example 1 and Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0037] 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.

[0038] Example 1

[0039] This embodiment provides a lithium-rich manganese-based positive electrode material, and the preparation method of the lithium-rich manganese-based positive electrode material is as follows:

[0040] (1) Lithium-rich manganese-based precursor Ni 0.4 Mn 0.6 (OH)2 was pre-sintered at 500℃ for 5h to obtain the oxide precursor Ni 0.4 Mn 0.6 O2;

[0041] (2) The oxide precursor and the lithium source are mixed according to Li / TM=1.4:1, and calcined at 900°C for 12h to obtain the lithium-rich manganese-based positive electrode material.

[0042] Example 2

[0043] This embodiment provides a lithium-rich manganese-based positive electrode material, and the preparation method of the lithium-rich manganese-based positive electrode material is as follows:

[0044] (1) Lithium-rich manganese-based precursor Ni 0.35 Co 0.05 Mn 0.6 (OH)2 was pre-calcined at 300℃ for 7h to obtain the oxide precursor Ni 0.35 Co 0.05 Mn0.6 O2;

[0045] (2) The oxide precursor and the lithium source are mixed according to Li / TM=1.3:1, and calcined at 800°C for 14 hours to obtain the lithium-rich manganese-based positive electrode material.

[0046] Example 3

[0047] This embodiment provides a lithium-rich manganese-based positive electrode material, and the preparation method of the lithium-rich manganese-based positive electrode material is as follows:

[0048] (1) Lithium-rich manganese-based precursor Ni 0.32 Co 0.02 Mn 0.66 (OH)2 was pre-calcined at 600℃ for 3h to obtain the oxide precursor Ni 0.32 Co 0.02 Mn 0.66 O2;

[0049] (2) The oxide precursor and the lithium source are mixed according to Li / TM=1.2:1, and calcined at 1000°C for 10 hours to obtain the lithium-rich manganese-based positive electrode material.

[0050] Example 4

[0051] The only difference between this embodiment and embodiment 1 is that the calcination temperature is 750° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0052] Example 5

[0053] The only difference between this embodiment and embodiment 1 is that the calcination temperature is 1100° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0054] Comparative Example 1

[0055] The only difference between this comparative example and Example 1 is that Li / TM=1.5:1, and other conditions and parameters are exactly the same as those in Example 1.

[0056] Comparative Example 2

[0057] The only difference between this comparative example and Example 1 is that Li / TM=1.1:1, and the other conditions and parameters are exactly the same as those in Example 1.

[0058] Comparative Example 3

[0059] The only difference between this comparative example and Example 1 is that Li / TM=1.6:1, and the other conditions and parameters are exactly the same as those in Example 1.

[0060] Comparative Example 4

[0061] The only difference between this comparative example and Example 1 is that the pre-firing treatment 1 is not performed, and the other conditions and parameters are exactly the same as those in Example 1.

[0062] Performance testing:

[0063] The results of this test are all the results of the power-off test. The specific steps are as follows: First, the active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1, and the slurry is mixed using a homogenizer in a multi-stage mode at room temperature; then, the ground slurry is applied to the A1 foil with a coater and dried in a vacuum drying oven at 80°C for 8 hours. Finally, the aluminum foil is punched into 1.13cm 2 The positive electrode was obtained by forming a circular shape. The resulting electrode sheet was used as the positive electrode, a metal sheet was used as the counter electrode, and a porous polypropylene membrane (Celgard 2400, USA) was used as a separator to separate the positive and counter electrodes. CR-2032 batteries were assembled in an Ar-filled glove box. The batteries were tested using a battery testing system (Blue Power CT2001A, Wuhan, China). The batteries were first activated three times at a rate of 0.1C within a voltage range of 2.0 to 4.8V. The activated button cells were then subjected to cycle and rate testing at different rates within the same voltage range. The test results are shown in Table 1.

[0064] Table 1

[0065] As can be seen from Table 1, from Examples 1-5, the discharge capacity of the battery made of the lithium-rich manganese-based positive electrode material described in the present application can reach more than 245.53 mAh / g, the capacity retention rate of 50 weeks is more than 95.2%, and the capacity retention rate of 100 weeks is more than 87.83% (by appropriately adjusting the type of precursor, the discharge capacity can reach a maximum of 273.93 mAh / g, the capacity retention rate of 50 weeks is 99.57%, and the capacity retention rate of 100 weeks is 98.24%).

[0066] By comparing Example 1 with Examples 4-5, it can be seen that the calcination temperature in the preparation process of the lithium-rich manganese-based positive electrode material described in the present application will affect its performance. When the calcination temperature is controlled at 800-1000°C, the performance of the positive electrode material obtained is better. If the calcination temperature is too low, the positive electrode surface is relatively loose, and the migration of lithium ions is hindered, which ultimately leads to a decrease in the performance of the lithium-rich manganese positive electrode. If the calcination temperature is too high, the positive electrode surface is severely agglomerated, further affecting the migration and diffusion of lithium ions, and ultimately leading to a decrease in performance.

[0067] By comparison between Example 1 and Comparative Examples 1-2, it can be seen that in the preparation process of the lithium-rich manganese-based positive electrode material described in the present application, the ratio of the lithium element in the lithium source to the metal element in the precursor has a very obvious effect on the material. When Li / TM is controlled at 1.2 to 1.4, the lithium-rich manganese-based positive electrode material exhibits good performance. If the amount of lithium added is too high, the residual alkali on the surface of the lithium-rich manganese-based positive electrode is too high, affecting the performance. If the amount of lithium added is too low, the lithium-rich manganese-based positive electrode impurities are generated, which will also affect the electrochemical properties of the lithium-rich manganese-based positive electrode.

[0068] From the comparison between Example 1 and Comparative Example 3, it can be seen that the lithium-rich manganese-based positive electrode material described in the present application is different from the lithium-rich manganese-based positive electrode material prepared by the related technology. The higher the lithium content (Li / TM exceeds 1.5), the further the performance decreases, which indirectly illustrates the particularity of the structure of the lithium-rich manganese-based positive electrode material described in the present application.

[0069] From the comparison between Example 1 and Comparative Example 4, it can be seen that the present application pre-sintering the lithium-rich manganese-based precursor in advance can maintain the stability of the structure and morphology of the precursor.

[0070] The XRD comparison diagrams of Example 1-2, Comparative Example 1 and Comparative Example 3 are shown in Figure 1-2. It can be seen from Figure 1-2 that as the lithium ratio decreases, the XRD front position shifts to a certain extent, indicating that lithium vacancies are generated during the lithium calcination process.

[0071] The capacity performance comparison diagram of Examples 1-2, Comparative Example 1 and Comparative Example 3 is shown in FIG3 . As can be seen from FIG3 , appropriately reducing the lithium content of the lithium-rich manganese-based positive electrode during the lithium addition process helps to improve the capacity of the lithium-rich manganese-based positive electrode.

[0072] A comparison of the cycle performance of Examples 1-2, Comparative Example 1 and Comparative Example 3 is shown in FIG4 . As can be seen from FIG4 , appropriately reducing the lithium content of the lithium-rich manganese-based positive electrode during the lithium addition process allows a protective coating with lithium vacancies, spinel and nickel doping to be generated on the surface of the lithium-rich manganese-based positive electrode, which helps to improve the cycle stability of the lithium-rich manganese-based positive electrode.

[0073] A comparison chart of the rate performance of Examples 1-2, Comparative Example 1 and Comparative Example 3 is shown in FIG5 . As can be seen from FIG5 , appropriately reducing the lithium content of the lithium-rich manganese-based positive electrode during the lithium addition process improves the surface structure of the lithium-rich manganese-based positive electrode, thereby helping to improve the rate performance of the lithium-rich manganese-based positive electrode.

[0074] 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 lithium-rich manganese-based positive electrode material, the method comprising the following steps: (1) pre-calcining a lithium-rich manganese-based precursor to obtain an oxide precursor; (2) mixing the oxide precursor and a lithium source, and subjecting the mixture to a calcination treatment to obtain the lithium-rich manganese-based positive electrode material; Wherein, the molar ratio of the total molar amount of the metal elements in the oxide precursor to the lithium element in the lithium source is 1:(1.2-1.4).

2. The preparation method according to claim 1, wherein The chemical formula of the lithium-rich manganese-based precursor in step (1) is Ni x Co y Mn 1-x-y (OH)2, wherein 0.4≥x>0.3, y<0.

1.

3. The preparation method according to claim 1 or 2, wherein: The temperature of the pre-sintering treatment in step (1) is 300-600°C.

4. The preparation method according to any one of claims 1 to 3, wherein The pre-burning treatment time is 3 to 7 hours.

5. The preparation method according to any one of claims 1 to 4, wherein: The lithium source in step (2) includes lithium carbonate and / or lithium hydroxide.

6. The preparation method according to any one of claims 1 to 5, wherein: The temperature of the calcination treatment in step (2) is 800-1000°C.

7. The preparation method according to any one of claims 1 to 6, wherein: The calcination time is 10 to 14 hours.

8. A lithium-rich manganese-based positive electrode material, wherein: The lithium-rich manganese-based positive electrode material is prepared by the method according to any one of claims 1 to 7.

9. The lithium-rich manganese-based positive electrode material according to claim 8, wherein: The lithium-rich manganese-based positive electrode material comprises a lithium-rich manganese-based core and a composite coating layer arranged on the surface of the lithium-rich manganese-based core.

10. The lithium-rich manganese-based positive electrode material according to claim 9, wherein: The composite coating layer contains lithium vacancies, spinel phase and nickel-doped coating.

11. A positive electrode sheet, wherein: The positive electrode plate comprises the lithium-rich manganese-based positive electrode material as claimed in claim 9 or 10.

12. A lithium ion battery, wherein: The lithium-ion battery comprises the positive electrode sheet as claimed in claim 11.

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