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 a use thereof. The preparation method comprises the following steps: (1) mixing a nickel source, a manganese source and a boron source with a solvent to obtain a mixed salt solution, and concurrently adding the mixed salt solution, an alkali solution and ammonia water into a base solution for a co-precipitation reaction to obtain a boron-doped positive electrode precursor; (2) calcining the boron-doped positive electrode precursor to obtain an oxide; and (3) mixing the oxide, a tungsten source and a lithium source, and sintering to obtain a lithium-rich manganese-based positive electrode material. An element B is added in the co-precipitation process, and is uniformly distributed in crystals, thereby enhancing the structural stability of the material; and an element W is doped in the lithiation calcination stage to form an isolation layer on the particle surface during calcination, thereby reducing side reactions during charge and discharge, and improving the cycle performance of the material.

Description

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

[0001] The present application belongs to the technical field of lithium-ion batteries and relates to a lithium-rich manganese-based positive electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-rich manganese-based xLi2MnO3·(1-x)LiMO2 materials have become a hot topic of research and development both domestically and internationally due to their high capacity (actual discharge capacity exceeding 250 mAh / g) and high voltage. Commercially available polycrystalline cathodes allow liquid electrolytes to penetrate their internal structure, increasing the number of reaction sites. However, these materials are prone to significant capacity fading and safety issues during long-term cycling.

[0003] Micron-sized single crystal materials can not only effectively alleviate surface and interfacial side reactions in the electrochemical process by reducing the specific surface area, but the reduction of porosity during particle aggregation also helps to improve the compaction density of the positive electrode and exhibit a higher lithium ion diffusion coefficient.

[0004] CN109956505A discloses a lithium-rich manganese-based positive electrode material, a preparation method and use thereof. The lithium-rich manganese-based positive electrode material is a flexible lithium-rich manganese-based positive electrode material that does not contain other inert components, thereby significantly improving its energy density.

[0005] CN113823786A discloses a method for preparing a modified lithium-rich manganese-based positive electrode material, wherein a single crystal fast lithium ion conductor coated lithium-rich manganese-based positive electrode material is obtained by simultaneously performing single crystal and surface coating treatments by ball milling.

[0006] Diffusion distance and diffusion coefficient play a joint role in capacity. One disadvantage of the single crystal cathode material described in the above scheme is that Li + The diffusion path is extended, resulting in Li + The uneven distribution eventually leads to cracks inside the crystal after long-term cycling at high voltage or high current density. In addition, when the positive electrode is cycled in a highly delithiated state, it undergoes an irreversible phase transition from H2 to H3, resulting in a sudden contraction of the lattice and the generation of nanocracks. Once cracks begin to form, capacity decay occurs.

[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 purpose of this application is to provide a lithium-rich manganese-based positive electrode material and its preparation method and application. This application focuses on the action principle of doping elements and performs doping separately in the co-precipitation stage and calcination stage to maximize the effect of doping modification. By uniformly doping the B element inside the single crystal, the interlayer spacing is expanded, which is beneficial to lithium ion transmission and achieves a stable crystal structure; by doping the W element, a stable interface is formed, which alleviates the gas production and structural collapse caused by the reaction of oxygen-containing components with the electrolyte. Through material modification, good rate performance and long cycle stability can be achieved.

[0010] To achieve this goal, this application adopts the following technical solutions:

[0011] 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:

[0012] (1) mixing a nickel source, a manganese source, and a boron source with a solvent to obtain a mixed salt solution, and adding the mixed salt solution, an alkali solution, and an ammonia solution to a bottom liquid in parallel for a coprecipitation reaction to obtain a boron-doped positive electrode precursor;

[0013] (2) calcining the boron-doped positive electrode precursor to obtain an oxide;

[0014] (3) The oxide, tungsten source and lithium source are mixed and sintered to obtain the lithium-rich manganese-based positive electrode material.

[0015] The present application adds the B element during the coprecipitation process so that it can be evenly distributed in the crystal, thereby enhancing the structural stability of the material; and by incorporating the W element during the lithiation calcination stage, an isolation layer is formed on the surface of the particles during calcination, thereby reducing side reactions during the charge and discharge process and improving the cycle performance of the material.

[0016] In one embodiment, the nickel source in step (1) includes any one of nickel chloride, nickel sulfate or nickel nitrate, or a combination of at least two thereof.

[0017] In one embodiment, the manganese source includes any one of manganese chloride, manganese sulfate, or manganese nitrate, or a combination of at least two thereof.

[0018] In one embodiment, the boron source comprises boron oxide and / or boric acid.

[0019] In one embodiment, the molar ratio of the total molar amount of the nickel source and the manganese source to the boron element in the boron source is (99.5-99.98):(0.02-0.5), for example: 99.98:0.02, 99.95:0.05, 99.9:0.1, 99.7:0.3 or 99.5:0.5, etc.

[0020] In one embodiment, the total molar concentration of nickel and manganese in the mixed salt solution of step (1) is 1 to 3 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L.

[0021] In one embodiment, the alkali solution includes sodium hydroxide solution and / or potassium hydroxide solution.

[0022] In one embodiment, the concentration of the alkali solution is 8 to 10 mol / L, for example, 8 mol / L, 8.5 mol / L, 9 mol / L, 9.5 mol / L or 10 mol / L.

[0023] In one embodiment, the concentration of the ammonia water is 8 to 10 mol / L, for example, 8 mol / L, 8.5 mol / L, 9 mol / L, 9.5 mol / L or 10 mol / L.

[0024] In one embodiment, the temperature of the coprecipitation reaction in step (1) is 40-80°C, for example, 40°C, 50°C, 60°C, 70°C or 80°C.

[0025] In one embodiment, the pH of the coprecipitation reaction is 8 to 12, for example, 8, 9, 10, 11 or 12.

[0026] In one embodiment, the temperature of the calcination treatment in step (2) is 600-950°C, for example, 600°C, 700°C, 800°C, 900°C or 950°C.

[0027] In one embodiment, the calcination treatment time is 6 to 10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours.

[0028] In one embodiment, the tungsten source in step (3) comprises WO3.

[0029] In one embodiment, the molar ratio of the oxide to the tungsten source is 100:(0.02-0.5), for example, 100:0.02, 100:0.05, 100:0.1, 100:0.3 or 100:0.5.

[0030] In one embodiment, the lithium source comprises lithium hydroxide and / or lithium carbonate.

[0031] In one embodiment, the sintering temperature in step (3) is 900-1000°C, for example, 900°C, 920°C, 950°C, 980°C or 1000°C.

[0032] In one embodiment, the sintering treatment time is 6 to 10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours.

[0033] 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.

[0034] In the lithium-rich manganese-based cathode material described in this application, B occupies the tetrahedral interstitial position of the oxygen-filled lattice, forming a stronger BO covalent bond, blocking the migration channel of the transition metal ions. The uniform distribution of the B element inside the crystal can achieve an ideal stable structure, effectively alleviating the concentration gradient distribution of lithium ions in micron-sized single crystals, causing serious lattice mismatch between the bulk and the surface, and the accumulation of microstress and strain in the grains. W is added together with the lithium source during lithiation calcination without adding additional synthesis processes. W reacts with the lithium source during heat treatment to form an LWO layer on the surface of the single crystal, which helps to improve mechanical strength. The charge accumulation around W is greater than that of Ni, forming a WO bond stronger than Ni-O, strengthening the interface and improving surface stability.

[0035] 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.

[0036] 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.

[0037] Compared with the prior art, this application has the following beneficial effects:

[0038] (1) This application focuses on the principle of action of doping elements and performs doping in the co-precipitation stage and the calcination stage respectively, to maximize the effect of doping modification. By uniformly doping the B element inside the single crystal, the interlayer spacing is expanded, which is beneficial to lithium ion transmission and achieves a stable crystal structure; by doping the W element, a stable interface is formed, which alleviates the gas production and structural collapse caused by the reaction of oxygen-containing components with the electrolyte. Through material modification, good rate performance and long-cycle stability can be achieved.

[0039] (2) The lithium-rich manganese-based positive electrode material described in the present application is used to make a battery with a capacity retention rate of more than 97.5% after 500 cycles of 1C cycling, a 0.5C discharge specific capacity of more than 255.1mAh / g, a 1C discharge specific capacity of more than 245.6mAh / g, a 2C discharge specific capacity of more than 226.3mAh / g, a 5C discharge specific capacity of more than 210.5mAh / g, and a 10C discharge specific capacity of more than 187.1mAh / g. The co-doping of an appropriate amount of metal W and non-metal B can stabilize the material structure and improve the transmission of lithium ions. The material performance is judged by preparing different lithium-rich manganese-based positive electrode materials. The test is simple and the results are highly reliable, which proves that the performance is best when the appropriate doping amounts of W and B are used.

[0040] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] 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.

[0042] FIG1 is a SEM image of the lithium-rich manganese-based positive electrode material described in Example 1 of the present application. DETAILED DESCRIPTION

[0043] 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.

[0044] Example 1

[0045] 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:

[0046] (1) nickel salt, manganese salt and boron compound are prepared into a mixed salt solution according to the stoichiometric ratio of Ni:Mn:B=0.249:0.75:0.001, and 10 mol / L liquid alkali solution and 9 mol / L ammonia water are prepared. Under nitrogen protection, the mixed salt solution, alkali solution and ammonia water are added to the reactor through metering pumps respectively. The coprecipitation reaction is carried out at 45°C and pH 11. When the average particle size of the material in the reactor reaches 4 μm, the feeding is stopped, the solution in the reactor is centrifuged and washed, and then dried to obtain a B-doped lithium-rich manganese-based positive electrode precursor;

[0047] (2) placing the prepared precursor in a calcining furnace at 650°C for 6 hours to obtain the corresponding oxide;

[0048] (3) The precursor oxide was mixed with WO3 and a lithium source at a molar ratio of precursor oxide: W: Li = 1:0.001:1.15 at high speed, and then calcined in a sintering furnace at 970° C. for 8 h to obtain the lithium-rich manganese-based positive electrode material. A SEM image of the lithium-rich manganese-based positive electrode material is shown in FIG1 .

[0049] Example 2

[0050] 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:

[0051] (1) nickel salt, manganese salt and boron compound were prepared into a mixed salt solution according to the stoichiometric ratio of Ni:Mn:B=0.2498:0.75:0.0002, and 9 mol / L liquid alkali solution and 8 mol / L ammonia water were prepared. Under nitrogen protection, the mixed salt solution, alkali solution and ammonia water were added to the reactor through metering pumps respectively. The coprecipitation reaction was carried out at 45°C and pH 11. When the average particle size of the material in the reactor reached 4 μm, the feeding was stopped, the solution in the reactor was centrifuged and washed, and then dried to obtain a B-doped lithium-rich manganese-based positive electrode precursor;

[0052] (2) placing the prepared precursor in a calcining furnace at 600°C for 6 hours to obtain the corresponding oxide;

[0053] (3) The above-mentioned precursor oxide is mixed with WO3 and a lithium source at a molar ratio of precursor oxide: W: Li = 1: 0.0002: 1.12 at a high speed, and then calcined at 900 ° C. for 10 hours in a sintering furnace to obtain the lithium-rich manganese-based positive electrode material.

[0054] Example 3

[0055] 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:

[0056] (1) nickel salt, manganese salt and boron compound are prepared into a mixed salt solution according to the stoichiometric ratio of Ni:Mn:B=0.245:0.75:0.005, and 10 mol / L liquid alkali solution and 9 mol / L ammonia water are prepared. Under nitrogen protection, the mixed salt solution, alkali solution and ammonia water are added to the reactor through metering pumps respectively. The coprecipitation reaction is carried out at 45°C and pH 11. When the average particle size of the material in the reactor reaches 4 μm, the feeding is stopped, the solution in the reactor is centrifuged and washed, and then dried to obtain a B-doped lithium-rich manganese-based positive electrode precursor;

[0057] (2) placing the prepared precursor in a calcining furnace at 950°C for 6 hours to obtain the corresponding oxide;

[0058] (3) The above-mentioned precursor oxide is mixed with WO3 and a lithium source at a molar ratio of precursor oxide: W: Li = 1:0.001:1.15 at a high speed, and then calcined at 1000°C in a sintering furnace for 6 hours to obtain the lithium-rich manganese-based positive electrode material.

[0059] Example 4

[0060] The only difference between this embodiment and embodiment 1 is that the molar ratio of the total molar amount of the nickel source and the manganese source to the boron element in the boron source is 99:1, and other conditions and parameters are exactly the same as those in embodiment 1.

[0061] Example 5

[0062] The only difference between this embodiment and embodiment 1 is that the molar ratio of the total molar amount of the nickel source and the manganese source to the boron element in the boron source is 99.99:0.01, and other conditions and parameters are exactly the same as those in embodiment 1.

[0063] Example 6

[0064] The only difference between this embodiment and embodiment 1 is that the molar ratio of the oxide to the tungsten source is 99:1, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0065] Example 7

[0066] The only difference between this embodiment and embodiment 1 is that the molar ratio of oxide to tungsten source is 99.99:0.01, and other conditions and parameters are exactly the same as those in embodiment 1.

[0067] Comparative Example 1

[0068] The only difference between this comparative example and Example 1 is that boron and tungsten are directly doped by co-precipitation, and other conditions and parameters are exactly the same as those in Example 1.

[0069] Comparative Example 2

[0070] The only difference between this comparative example and Example 1 is that no boron source is added, and other conditions and parameters are exactly the same as those in Example 1.

[0071] Example 3

[0072] The only difference between this comparative example and Example 1 is that no tungsten source is added, and other conditions and parameters are exactly the same as those in Example 1.

[0073] Performance testing:

[0074] The first-week charge-discharge capacity and cycle performance were measured using constant current charge-discharge mode at room temperature. The positive electrode material was assembled into a CR2025 button cell and cycled 100 times at 1C / 1C at 25°C with a voltage range of 2.5V to 4.6V. Rate performance was tested using current densities of 0.5C, 1C, 2C, 5C, and 10C. The test results are shown in Table 1.

[0075] Table 1

[0076] As can be seen from Table 1, it can be obtained from Examples 1-3 that the capacity retention rate of the battery made of the lithium-rich manganese-based positive electrode material described in the present application after 500 cycles of 1C cycle can reach more than 97.5%, the 0.5C discharge specific capacity can reach more than 255.1mAh / g, the 1C discharge specific capacity can reach more than 245.6mAh / g, the 2C discharge specific capacity can reach more than 226.3mAh / g, the 5C discharge specific capacity can reach more than 210.5mAh / g, and the 10C discharge specific capacity can reach more than 187.1mAh / g. The B and W co-doped lithium-rich manganese-based positive electrode materials with appropriate content ranges in the present application show excellent capacity retention and rate performance.

[0077] By comparison of Example 1 and Examples 4-5, it can be seen that in the lithium-rich manganese-based positive electrode material described in the present application, the amount of boron doping will affect its performance. During the preparation process, the molar ratio of the total molar amount of the nickel source and the manganese source to the boron element in the boron source is controlled at (99.5-99.98): (0.02-0.5). The performance of the lithium-rich manganese-based positive electrode material is good. If the boron doping amount is too large, the transitional substitution of boron in the crystal structure affects the performance of the transition metal capacity and even causes lattice distortion; if the boron doping amount is too small, the effect of widening the lithium ion channel cannot be achieved, and there is no obvious improvement on the diffusion and migration of lithium ions, and the capacity will also be limited.

[0078] By comparing Example 1 with Examples 6-7, it can be seen that in the lithium-rich manganese-based positive electrode material described in the present application, the amount of tungsten doping will affect its performance. During the preparation process, the molar ratio of the oxide and the tungsten source is controlled at 100: (0.02~0.5), and the performance of the lithium-rich manganese-based positive electrode material is good. If the tungsten doping amount is too large, the crystal internal resistance will increase, deteriorate the cycle performance of the material, and also deteriorate the rate performance; if the tungsten doping amount is too small, there is not enough W to diffuse to the crystal surface to form a stable isolation layer, and the cycle performance cannot be improved.

[0079] By comparing Example 1 and Comparative Example 1, it can be seen that the present application adds the B element during the co-precipitation process so that it can be evenly distributed in the crystal, thereby enhancing the structural stability of the material; by incorporating the W element during the lithiation calcination stage, an isolation layer is formed on the surface of the particles during calcination, thereby reducing side reactions during the charge and discharge process and improving the cycle performance of the material.

[0080] By comparison of Example 1 and Comparative Examples 2-3, it can be seen that in the lithium-rich manganese-based positive electrode material described in the present application, B occupies the tetrahedral interstitial position of the oxygen-filled lattice, forming a stronger BO covalent bond, blocking the migration channel of the transition metal ions, and the uniform distribution of the B element inside the crystal can achieve an ideal stable structure, effectively alleviating the concentration gradient distribution of lithium ions in micron-sized single crystals, causing serious lattice mismatch between the bulk and the surface, and the accumulation of microstress and strain in the grains. W is added together with the lithium source during lithiation calcination without adding additional synthesis processes. W reacts with the lithium source during the heat treatment process to form an LWO layer on the surface of the single crystal, which helps to improve the mechanical strength. The charge accumulation around W is greater than that of Ni, forming a WO bond stronger than Ni-O, strengthening the interface and improving surface stability.

[0081] 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 preparation method comprising the following steps: (1) mixing a nickel source, a manganese source and a boron source with a solvent to obtain a mixed salt solution, and adding the mixed salt solution, an alkali solution and an ammonia solution to a base liquid in parallel for a co-precipitation reaction to obtain a boron-doped positive electrode precursor; (2) calcining the boron-doped positive electrode precursor to obtain an oxide; (3) The oxide, tungsten source and lithium source are mixed, and the mixture is sintered to obtain the lithium-rich manganese-based positive electrode material.

2. The preparation method according to claim 1, wherein The nickel source in step (1) comprises any one of nickel chloride, nickel sulfate or nickel nitrate, or a combination of at least two thereof; Optionally, the manganese source includes any one or a combination of at least two of manganese chloride, manganese sulfate or manganese nitrate; Optionally, the boron source includes boron oxide and / or boric acid; Optionally, the molar ratio of the total molar amount of the nickel source and the manganese source to the boron element in the boron source is (99.5-99.98):(0.02-0.5).

3. The preparation method according to claim 1 or 2, wherein: The total molar concentration of nickel and manganese in the mixed salt solution of step (1) is 1 to 3 mol / L; Optionally, the alkali solution includes sodium hydroxide solution and / or potassium hydroxide solution; Optionally, the concentration of the alkali solution is 8 to 10 mol / L; Optionally, the concentration of the ammonia water is 8 to 10 mol / L.

4. The preparation method according to any one of claims 1 to 3, wherein The temperature of the coprecipitation reaction in step (1) is 40 to 80° C. Optionally, the pH of the coprecipitation reaction is 8-12.

5. The preparation method according to any one of claims 1 to 4, wherein: The calcination temperature in step (2) is 600-950°C; Optionally, the calcination treatment time is 6 to 10 hours.

6. The preparation method according to any one of claims 1 to 5, wherein: The tungsten source in step (3) comprises WO3; Optionally, the molar ratio of the oxide to the tungsten source is 100:(0.02-0.5); Optionally, the lithium source includes lithium hydroxide and / or lithium carbonate.

7. The preparation method according to any one of claims 1 to 6, wherein: The sintering temperature in step (3) is 900-1000° C. Optionally, the sintering treatment time is 6 to 10 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. A positive electrode plate, comprising the lithium-rich manganese-based positive electrode material according to claim 8. 10 . A lithium ion battery, comprising the positive electrode sheet according to claim 9 .

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