A lithium-rich manganese-based cathode material and its preparation method

Abstract

The present invention discloses a lithium-rich manganese-based cathode material and a preparation method thereof, belonging to the technical field of batteries. The chemical formula of the lithium-rich manganese-based cathode material is xLi<subgt;2< / subgt;MnO<subgt;3< / subgt>·(1−x)LiMO<subgt;2< / subgt>, where M is selected from Ni, Mn, Co, Cr or Fe; 0 < x ≤ 1; the cathode material has a spinel interface, and has a fast lithium ion transmission rate and high rate performance. The preparation method includes: subjecting a mixed material of a cathode material precursor and a lithium source to heat preservation treatment in an oxygen-containing atmosphere in a first low-temperature zone to decompose the mixed material; subsequently, subjecting it to heat preservation treatment in a high-temperature zone to generate a lithium-rich manganese-based material containing both a trigonal layered structure and a monoclinic layered structure; adjusting the oxygen-containing atmosphere to an anaerobic atmosphere, and making the surface of the lithium-rich manganese-based material in a lithium-deficient state under a slightly positive pressure condition; and then subjecting it to heat preservation treatment in a second low-temperature zone in an oxygen-containing atmosphere to obtain a lithium-rich manganese-based cathode material with an in-situ constructed spinel interface. This method has simple processes and reduces the introduction of impurities.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular, to a lithium-rich manganese-based cathode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have been widely used due to their advantages such as good cycling performance, high capacity, low price, convenience in use, safety, and environmental friendliness. With the development of transportation equipment such as electric vehicles, higher requirements are put forward for the performance of lithium batteries. The lithium-rich manganese-based cathode material has a high specific capacity (greater than 250 mAh / g) and a wide working voltage window (2 - 4.8 V), and is most likely to become the next-generation high-performance lithium-ion battery material. However, at present, the lithium-rich manganese-based cathode material has obvious defects such as low rate performance and poor cycle stability, which severely limits its use.

[0003] During the first charging process of the lithium-rich manganese-based cathode material, part of the Li + is removed in the form of Li2O, but cannot be re-embedded during the discharging process, resulting in a low first charge-discharge efficiency of this material. At the same time, the removal of Li2O will cause part of the lattice oxygen to be removed to generate oxygen, and the generation of oxygen will damage the surface of the electrode, making the electrode interior eroded by the electrolyte, resulting in poor stability, causing changes in the surface composition and structure of the material and gradually spreading to the interior, increasing the impedance of the battery and resulting in poor cycle performance of the material, seriously affecting the battery life.

[0004] Therefore, it is necessary to optimize the performance of the lithium-rich manganese-based cathode material by using technical means such as surface modification to change the surface structure of the lithium-rich manganese-based material.

[0005] Currently, metal oxides, metal fluorides, or phosphates are usually used to stabilize the surface structure of the lithium-rich manganese-based cathode material, thereby improving the performance of the lithium-rich manganese-based cathode material at normal and high temperatures. However, when using the above materials to optimize the lithium-rich manganese-based cathode material, the formed coating layer on the surface is discontinuous and cannot achieve a satisfactory effect.

[0006] In view of this, the present invention is specifically proposed. Summary of the Invention

[0007] One of the purposes of the present invention is to provide a lithium-rich manganese-based cathode material, which has a fast lithium-ion transmission rate and high rate performance. Another purpose of the present invention is to provide a preparation method of the above lithium-rich manganese-based cathode material.

[0008] The present application can be implemented as follows:

[0009] In a first aspect, the present application provides a lithium-rich manganese-based cathode material with a chemical formula of xLi2MnO3·(1-x)LiMO2, where M is selected from Ni, Mn, Co, Cr or Fe; and 0 < x ≤ 1;

[0010] The lithium-rich manganese-based cathode material has a spinel interface, and the lithium-rich manganese-based cathode material contains both a rhombic LiMO2 structure and a monoclinic Li2MnO3 structure.

[0011] In a second aspect, the present application provides a method for preparing the above lithium-rich manganese-based cathode material, including the following steps:

[0012] The mixed material of the lithium-rich manganese-based cathode material precursor and the lithium source is heat-insulated in an oxygen-containing atmosphere in a first low-temperature zone to decompose the mixed material; then it is heat-insulated in a high-temperature zone to generate a lithium-rich manganese-based material containing both a trigonal layered and a monoclinic layered structure; the oxygen-containing atmosphere is adjusted to an oxygen-free atmosphere, and the surface of the lithium-rich manganese-based material is in an under-lithiated state under a slightly positive pressure condition; then, in an oxygen-containing atmosphere, it is heat-insulated in a second low-temperature zone to obtain a lithium-rich manganese-based cathode material with an in-situ constructed spinel interface.

[0013] In an optional embodiment, the mass ratio of the lithium-rich manganese-based cathode material precursor to the lithium source is 2:0.8 - 1.2.

[0014] In an optional embodiment, the lithium-rich manganese-based cathode material precursor is a precursor in the form of a hydroxide or a precursor in the form of a carbonate.

[0015] In an optional embodiment, the lithium-rich manganese-based cathode material precursor is particles with a particle size of 1 - 15 μm.

[0016] In an optional embodiment, the temperature of the first low-temperature zone is 480 - 550 °C, and / or the heat-insulation time in the first low-temperature zone is 1 - 15 h.

[0017] In an optional embodiment, the temperature of the high-temperature zone is 800 - 1000 °C, and / or the heat-insulation time in the high-temperature zone is 1 - 15 h.

[0018] In an optional embodiment, the pressure condition corresponding to the slightly positive pressure is 1 - 20 Pa, and / or the holding time of the slightly positive pressure is 30 min - 7 h.

[0019] In an optional embodiment, the temperature of the second low-temperature zone is 550 - 750 °C, and / or the heat-insulation time in the second low-temperature zone is 1 - 8 h.

[0020] In an optional embodiment, each oxygen-containing atmosphere is provided by air and / or oxygen.

[0021] In an optional embodiment, the flow rate of air and / or oxygen is greater than 0 m3 / h and ≤ 10 m 3 / h.

[0022] In an alternative embodiment, the anaerobic atmosphere is provided by nitrogen and / or inert gas.

[0023] In an alternative embodiment, the flow rate of nitrogen and / or inert gas is greater than 0 m 3 / h and ≤ 10 m 3 / h.

[0024] In an alternative embodiment, the cooling rate from the high-temperature zone to the second low-temperature zone is 1 - 5 °C / min.

[0025] The beneficial effects of the present application include:

[0026] The preparation method provided by the present application enables the decomposition of the mixed material of the precursor and the lithium source through heat preservation treatment in the first low-temperature zone (through heat preservation treatment in the first low-temperature zone, the mixture of the precursor and the lithium source can be fully decomposed. For example, carbonates are decomposed into oxides and carbon dioxide, and hydroxides generate oxides and water, and then the decomposition products can react in the high-temperature zone to form a triclinic layered (dominant) and monoclinic layered structure. Moreover, the above-mentioned decomposed materials are more likely to come into contact with each other, making the subsequent reaction more complete), and then heat preservation treatment in the high-temperature zone to generate a lithium-rich manganese-based material containing both triclinic layered and monoclinic layered structures (during the heat preservation treatment of the lithium-rich manganese-based material in the high-temperature zone, a stable triclinic structure is first formed. Further, the excess lithium will also react to form a monoclinic structure of Li2MnO3 phase, making the final lithium-rich manganese-based material in a stable state of a two-phase structure). Then, under the conditions of an anaerobic atmosphere and a slightly positive pressure, the surface of the lithium-rich manganese-based material is in an under-lithiated state, and then through an oxygen-containing atmosphere and heat preservation treatment in the second low-temperature zone, a spinel interface is in-situ constructed on the under-lithiated structure.

[0027] This process is simple, easy to operate, and has a high yield, reduces the introduction of impurities, and effectively prepares a lithium-rich manganese-based cathode material with an in-situ constructed spinel interface.

[0028] In the obtained material, the interface bonding strength between the in-situ constructed spinel structure and the matrix layered structure is relatively high, which not only has high structural stability, avoids the shedding of the surface spinel structure due to structural stress during repeated charge and discharge cycles of the material, but also forms a three-dimensional lithium-ion diffusion channel, ensures the smoothness of the lithium-ion diffusion channel during charge and discharge, and can accelerate the lithium-ion transmission rate, which is beneficial to improving the rate performance of the material. Description of the Drawings

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0030] Figure 1 XRD pattern of each cathode material in Test Example 1;

[0031] Figure 2 and Figure 3 is Figure 1 partial enlarged view of;

[0032] Figure 4 Initial charge-discharge curve corresponding to Test Example 2;

[0033] Figure 5 Cycling performance curve corresponding to Test Example 2. Detailed implementation manners

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0035] The lithium-rich manganese-based cathode material and its preparation method provided in the present application will be specifically described below.

[0036] The present application proposes a lithium-rich manganese-based cathode material with the chemical formula xLi2MnO3·(1 - x)LiMO2, where M is selected from Ni, Mn, Co, Cr, or Fe; and 0 < x ≤ 1.

[0037] The lithium-rich manganese-based cathode material has a spinel interface and simultaneously contains a rhombic LiMO2 structure and a monoclinic Li2MnO3 structure, enabling the lithium-rich manganese-based cathode material to have a fast lithium-ion transmission rate and high rate performance.

[0038] By reference, the precursor of the lithium-rich manganese-based cathode material corresponding to the above lithium-rich manganese-based cathode material can be a precursor in the form of a hydroxide or a precursor in the form of a carbonate.

[0039] By way of example but not limitation, the precursor in the form of a hydroxide can be Ni 0.35 Co 0.05 Mn 0.6 (OH)2, and the precursor in the form of a carbonate can be Ni0.35 Co 0.05 Mn 0.6 CO3。

[0040] Correspondingly, the present application also provides a method for preparing the above-mentioned lithium-rich manganese-based cathode material, including the following steps:

[0041] The mixed material of the lithium-rich manganese-based cathode material precursor and the lithium source is heat-preserved in an oxygen-containing atmosphere in a first low-temperature zone to decompose the mixed material; subsequently, it is heat-preserved in a high-temperature zone to generate a lithium-rich manganese-based material containing both trigonal layered and monoclinic layered structures; the oxygen-containing atmosphere is adjusted to an anaerobic atmosphere, and the surface of the lithium-rich manganese-based material is made lithium-deficient under a slightly positive pressure condition; then, it is heat-preserved in an oxygen-containing atmosphere in a second low-temperature zone to obtain a lithium-rich manganese-based cathode material with an in-situ constructed spinel interface.

[0042] As a reference, the lithium-rich manganese-based cathode material precursor can be particles (which can also be understood as powders) with a particle size of 1-15 μm. Specifically, the particle size can be 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, etc., or any other value within the range of 1-15 μm.

[0043] It should be noted that if the particle size of the lithium-rich manganese-based cathode material precursor is too small, the contact area with the electrolyte will increase, resulting in an increase in side reactions between the material and the electrolyte, affecting the cycling performance of the material; if the particle size of the lithium-rich manganese-based cathode material precursor is too large, the lithium ion transport path will be too long, affecting the rate performance of the material.

[0044] The lithium source can be lithium hydroxide or lithium carbonate, etc.

[0045] Preferably, the mass ratio of the lithium-rich manganese-based cathode material precursor to the lithium source can be 2:0.8-1.2, such as 2:0.8, 2:0.85, 2:0.9, 2:0.95, 2:1, 2:1.05, 2:1.1, 2:1.15, or 2:1.2, etc., or any other value within the range of 2:0.8-1.2.

[0046] The oxygen-containing atmosphere mentioned in the present application is provided by air and / or oxygen.

[0047] For reference, the flow rate of air and / or oxygen can be, for example, greater than 0 m 3 / h and ≤10 m 3 / h, such as 0.1 m 3 / h, 0.5 m 3 / h, 1 m 3 / h, 2 m 3 / h, 5 m 3 / h, 8 m 3 / h or 10 m 3 / h, etc., and can also be greater than 0m 3 / h and ≤ 10m 3 / h and any other value within the range.

[0048] As a reference, the temperature of the first low-temperature zone can be 480 - 550 °C, such as 480 °C, 490 °C, 500 °C, 510 °C, 520 °C, 530 °C, 540 °C or 550 °C, etc., and can also be any other value within the range of 480 - 550 °C.

[0049] The heat preservation time of the first low-temperature zone can be 1 - 15h, such as 1h, 2h, 5h, 8h, 10h, 12h or 15h, etc., and can also be any other value within the range of 1 - 15h.

[0050] The heat preservation treatment in the first low-temperature zone can be carried out in a box furnace. Under the above heat preservation treatment conditions in the first low-temperature zone, the mixture of the precursor and the lithium source can be fully decomposed. For example, carbonates are decomposed into oxides and carbon dioxide, and hydroxides are converted into oxides and water. On the one hand, it is beneficial for the decomposition products to react with each other in the high-temperature zone to form a tri-layered (mainly) and monoclinic layered structure (specifically, during the heat preservation treatment in the high-temperature zone of the lithium-rich manganese-based material, a stable tri-layered structure is first formed, which is the lithium-rich material; further, the excess lithium also reacts to form the Li2MnO3 phase with a monoclinic structure, making the final lithium-rich manganese-based material in a stable state of a two-phase structure); on the other hand, the decomposed materials are more likely to come into contact with each other, making the subsequent reaction more complete.

[0051] After the heat preservation treatment in the first low-temperature zone is completed, the temperature is raised to the high-temperature zone for heat preservation treatment.

[0052] As a reference, the temperature of the high-temperature zone can be 800 - 1000 °C, such as 800 °C, 820 °C, 850 °C, 880 °C, 900 °C, 920 °C, 950 °C, 980 °C or 1000 °C, etc., and can also be any other value within the range of 800 - 1000 °C.

[0053] The heat preservation time of the high-temperature zone can be 1 - 15h, such as 1h, 2h, 5h, 8h, 10h, 12h or 15h, etc., and can also be any other value within the range of 1 - 15h.

[0054] If the temperature of the high-temperature zone is too high, it is easy to cause the corresponding structure to be damaged; if the temperature is too low, the structure is likely to be unstable.

[0055] In this application, the anaerobic atmosphere is provided by nitrogen and / or inert gas (such as argon).

[0056] For reference, the flow rate of nitrogen and / or inert gas can be greater than 0m 3 / h and ≤ 10m 3 / h, such as 0.1 m 3 / h, 0.5 m 3 / h, 1 m 3 / h, 2 m 3 / h, 5 m 3 / h, 8 m 3 / h or 10 m 3 / h, etc., and can also be greater than 0 m 3 / h and ≤ 10 m 3 / h and any other arbitrary value within the range.

[0057] Specifically, the anaerobic atmosphere can be achieved by changing the introduced air and / or oxygen to inert gas and / or nitrogen after the treatment in the high-temperature zone.

[0058] For reference, the pressure condition corresponding to the slightly positive pressure can be 1 - 20 Pa, such as 1 Pa, 2 Pa, 5 Pa, 8 Pa, 10 Pa, 12 Pa, 15 Pa, 18 Pa or 20 Pa, etc., and can also be any other arbitrary value within the range of 1 - 20 Pa.

[0059] The holding time of the slightly positive pressure can be 30 min - 7 h, such as 30 min, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h or 7 h, etc., and can also be any other arbitrary value within the range of 30 min - 7 h.

[0060] Under the conditions of slightly positive pressure and introducing argon and / or inert gas, the lithium ions on the surface of the material are promoted to escape, and the inert gas can take away some of the lithium ions on the surface of the positive electrode material, thereby reducing the lithium ion content on the surface, and the surface of the lithium-rich manganese-based material shows a lithium-deficient state.

[0061] It should be noted that if the holding time of the slightly positive pressure is too long, phase transformation may occur and the structure may be damaged.

[0062] For reference, the temperature of the second low-temperature zone can be 550 - 750 °C, such as 550 °C, 580 °C, 600 °C, 620 °C, 650 °C, 680 °C, 700 °C, 720 °C or 750 °C, etc., and can also be any other arbitrary value within the range of 550 - 750 °C.

[0063] The heat preservation time of the second low-temperature zone can be 1 - 8 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h or 8 h, etc., and can also be any other arbitrary value within the range of 1 - 8 h.

[0064] During the heat preservation treatment stage in the second low-temperature zone, the lithium-deficient structure on the surface layer of the lithium-rich manganese-based material can in-situ generate a spinel structure.

[0065] Exemplarily, the cooling rate from the above-mentioned high-temperature region to the second low-temperature region can be 1-5 °C / min, such as 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min or 5 °C / min, etc., or any other value within the range of 1-5 °C / min.

[0066] Further, after the heat preservation treatment in the second low-temperature region, conventional operations such as cooling, crushing, and sieving can also be carried out.

[0067] The above preparation method has a simple process, convenient operation, high yield, and reduces the introduction of impurities.

[0068] The interfacial bonding strength between the spinel structure and the matrix layered structure in-situ constructed by the above method is relatively high. It not only has high structural stability, avoiding the shedding of the surface spinel structure due to structural stress during repeated charge and discharge cycles, but also the lithium-ion diffusion channels in the two crystal structures (rhombic LiMO2 structure and monoclinic Li2MnO3 structure) are interconnected to form a three-dimensional lithium-ion diffusion channel, ensuring the smoothness of the lithium-ion diffusion channel during charge and discharge, and can accelerate the lithium-ion transmission rate, which is beneficial to improving the rate performance of the material.

[0069] The features and properties of the present invention will be further described in detail below in conjunction with the embodiments.

[0070] Example 1

[0071] This example provides a lithium-rich manganese-based cathode material with an in-situ constructed spinel interface, and its preparation method includes the following steps:

[0072] Step 1: Prepare the lithium-rich manganese-based precursor powder Ni 0.35 Co 0.05 Mn 0.6 (OH)2, and the average particle size of this precursor material is 4 μm.

[0073] Step 2: Weigh 2000 g of the lithium-rich manganese-based precursor material powder in Step 1 and uniformly mix it with 1000 g of lithium carbonate.

[0074] Step 3: Put the material in Step 2 into a box furnace, and introduce air. The flow rate of the air is 5 m 3 / h. Keep it at 500 °C in the low-temperature region for 5 h to decompose the material, and then raise the temperature to 850 °C and keep it for 10 h to generate a layered lithium-rich manganese-based cathode material.

[0075] Step 4: After Step 3 is completed, change the introduced air to nitrogen, and the flow rate of the nitrogen is 8 m 3 / h, and maintain the slightly positive pressure of the furnace at 5 Pa. After maintaining for 1 h, let nitrogen remove some lithium ions on the surface of the cathode material. Then cool down to 650 °C at a rate of 2 °C / min and hold for 5 h. During the holding stage, change the nitrogen to air, and the flow rate of the air is 5 m 3 / h. After cooling, crushing, and sieving after the holding is completed, the lithium-rich manganese-based cathode material with an in-situ constructed spinel interface is obtained.

[0076] Example 2

[0077] The difference between this example and Example 1 is that:

[0078] Step 4: After Step 3 is completed, change the introduced air to nitrogen, and the flow rate of the nitrogen is 10 m 3 / h, and maintain the slightly positive pressure of the furnace at 5 Pa. After maintaining for 1 h, let nitrogen remove some lithium ions on the surface of the cathode material. Then cool down to 700 °C at a rate of 2 °C / min and hold for 3 h. During the holding stage, change the nitrogen to air, and the flow rate of the air is 5 m 3 / h. After cooling, crushing, and sieving after the holding is completed, the lithium-rich manganese-based cathode material with an in-situ constructed spinel interface is obtained.

[0079] Example 3

[0080] This example provides a lithium-rich manganese-based cathode material with an in-situ constructed spinel interface, and its preparation method includes the following steps:

[0081] Step 1: Prepare the lithium-rich manganese-based precursor powder Ni 0.35 Co 0.05 Mn 0.6 (OH)2, and the average particle size of this precursor material is 1 μm.

[0082] Step 2: Weigh 2000 g of the lithium-rich manganese-based precursor material powder in Step 1 and uniformly mix it with 1000 g of lithium hydroxide.

[0083] Step 3: Put the material in Step 2 into a box furnace, and introduce air, and the flow rate of the air is 2 m 3 / h. Hold at 480 °C in the low-temperature zone for 15 h to decompose the material, and then raise the temperature to 800 °C and hold for 15 h to generate a layered lithium-rich manganese-based cathode material.

[0084] Step 4: After Step 3 is completed, change the introduced air to nitrogen, and the flow rate of the nitrogen is 2 m 3 / h, and maintain the slightly positive pressure of the furnace at 1 Pa. After maintaining for 7 h, let nitrogen remove some lithium ions on the surface of the cathode material. Then cool down to 550 °C at a rate of 1 °C / min and hold for 8 h. During the holding stage, change the nitrogen to air, and the flow rate of the air is 2 m 3After heat preservation at [specific temperature] / h, after cooling, crushing, and sieving, the lithium-rich manganese-based cathode material with in-situ constructed spinel interface is obtained.

[0085] Example 4

[0086] This example provides a lithium-rich manganese-based cathode material with in-situ constructed spinel interface, and its preparation method includes the following steps:

[0087] Step 1: Prepare the lithium-rich manganese-based precursor powder Ni 0.35 Co 0.05 Mn 0.6 CO3, and the average particle size of this precursor material is 15 μm.

[0088] Step 2: Weigh 2000 g of the lithium-rich manganese-based precursor material powder in Step 1 and mix it evenly with 1000 g of lithium carbonate.

[0089] Step 3: Put the material in Step 2 into a box furnace, introduce oxygen, and the flow rate of oxygen is 8 m 3 / h. Keep it at 550 °C in the low-temperature zone for 1 h to decompose the material, then raise the temperature to 1000 °C and keep it for 1 h to generate a layered lithium-rich manganese-based cathode material.

[0090] Step 4: After Step 3 is completed, change the introduced oxygen to argon, and the flow rate of argon is 8 m 3 / h, and keep the slight positive pressure of the furnace at 20 Pa. After keeping it for 30 min, let the argon take away some lithium ions on the surface of the cathode material, then cool it down to 750 °C at 5 °C / min and keep it for 1 h. During the heat preservation stage, change the argon to oxygen, and the flow rate of oxygen is 8 m 3 / h. After heat preservation, perform cooling, crushing, and sieving, and then the lithium-rich manganese-based cathode material with in-situ constructed spinel interface is obtained.

[0091] Comparative Example 1

[0092] The difference between this comparative example and Example 1 is that only Steps 1 - 3 are included, without Step 4; that is, the layered lithium-rich manganese-based cathode material obtained in Step 3 of Example 1 is provided in this comparative example.

[0093] Test Example 1

[0094] Taking Example 1 and Comparative Example 1 as examples, the XRD patterns of the lithium-rich manganese-based cathode material with in-situ constructed spinel interface prepared in Example 1 and the layered lithium-rich manganese-based cathode material of the comparative example are as Figures 1 to 3 shown.

[0095] From Figures 1 to 3It can be seen that the in-situ construction of the spinel interface of the lithium-rich manganese-based cathode material does not change the main crystal structure of the original lithium-rich manganese-based cathode material. Both are typical α-NaFeO2 structures, belonging to the R-3m space group, with obvious splitting of the (006) / (012) and (018) / (110) peaks, and the superlattice peaks of Li2MnO3 appear between θ = 20° and 22°. However, from the local enlarged images at θ = 18° to 20° and θ = 44° to 46°, it can be seen that the (003) peak and (104) peak of the modified cathode material are slightly shifted to lower angles relative to the original lithium-rich manganese-based cathode material, indicating that the interlayer spacing of the modified cathode material is larger than that of the original lithium-rich manganese-based cathode material, which will be conducive to the insertion and extraction of lithium ions, and the surface of the surface-modified sample has a spinel phase.

[0096] Test Example 2

[0097] Taking the materials obtained in Example 1 and Comparative Example 1 as examples, electrodes were prepared and batteries were assembled in the following manners.

[0098] Electrode preparation and battery assembly: Each lithium-rich manganese-based positive electrode material was weighed and fully mixed with super carbon black and polyvinylidene fluoride (PVDF) in a mass ratio of 9:0.5:0.5, coated on aluminum foil, and placed in a vacuum dryer at 100°C for 5 hours. After taking it out, it was placed on a roller press and rolled several times, and then cut into discs. It was used as the positive electrode, the metal lithium sheet as the negative electrode, the polypropylene microporous membrane as the separator, and 1 mol / L LiPF6+EC / DMC / EMC as the electrolyte. The CR2430 stainless steel button battery was assembled in a glove box filled with argon and with a moisture content of less than 0.1ppm; after standing for 10 hours, its charge and discharge performance was tested.

[0099] Figure 4 These are the first cycle charge and discharge curves of Example 1 and Comparative Example 1.

[0100] Depend on Figure 4 As can be seen, under the test conditions of a voltage of 2.0-4.8V and a rate of 0.1C, Example 1 achieves an initial discharge capacity of 248mAh / g and a first efficiency of 85.16%. The discharge curve of this sample exhibits a distinct plateau near 2.6V, allowing the material to incorporate more lithium ions, which contributes to improved discharge capacity and coulombic efficiency. This plateau corresponds to the reduction reaction of manganese in the spinel phase.

[0101] The material corresponding to Comparative Example 1, under the test conditions of voltage of 2.0-4.8V and rate of 0.1C, has an initial discharge capacity of 236.9mAh / g and a first efficiency of 83.9%.

[0102] Figure 5 1 is the cycle performance curve of Example 1 and Comparative Example 1.

[0103] It can be seen from Figure 5 that under the test conditions of a voltage of 2.0 - 4.8 V and a rate of 0.5 C, the material corresponding to Example 1 still had a discharge specific capacity of 208.3 mA / g after 100 cycles, and its capacity retention rate was 84%.

[0104] For the material corresponding to Comparative Example 1, the discharge specific capacity was only 189.8 mAh / g after 100 cycles at 0.5 C, and its capacity retention rate was 80.1%.

[0105] Test Example 3

[0106] Taking Examples 2 - 4 as examples, the electrode preparation, battery assembly and corresponding performance tests were carried out according to the method in Test Example 2.

[0107] The results are as follows:

[0108] For the material corresponding to Example 2, under the test conditions of a voltage of 2.0 - 4.8 V and a rate of 0.1 C, its initial discharge specific capacity was 242.8 mAh / g, and its first efficiency was 84.5%. After 100 cycles at 0.5 C, the discharge specific capacity was still 199.8 mAh / g, and its capacity retention rate was 82.3%.

[0109] For the material corresponding to Example 3, under the test conditions of a voltage of 2.0 - 4.8 V and a rate of 0.1 C, its initial discharge specific capacity was 247 mAh / g, and its first efficiency was 85.2%. After 100 cycles at 0.5 C, the discharge specific capacity was still 201.6 mAh / g, and its capacity retention rate was 81.6%.

[0110] For the material corresponding to Example 4, under the test conditions of a voltage of 2.0 - 4.8 V and a rate of 0.1 C, its initial discharge specific capacity was 241 mAh / g, and its first efficiency was 85%. After 100 cycles at 0.5 C, the discharge specific capacity was still 195.9 mAh / g, and its capacity retention rate was 81.3%.

[0111] In summary, the preparation method provided by this application has a simple process, is easy to operate, has a high yield, reduces the introduction of impurities, and effectively prepares a lithium-rich manganese-based cathode material with an in-situ constructed spinel interface. In the obtained material, the interface between the in-situ constructed spinel structure and the matrix layered structure has a high binding strength, which not only has high structural stability, avoids the shedding of the surface spinel structure during repeated charge and discharge cycles due to structural stress, but also forms a three-dimensional lithium-ion diffusion channel, ensuring the smoothness of the lithium-ion diffusion channel during charge and discharge, and can accelerate the lithium-ion transmission rate, which is beneficial to improving the rate performance of the material.

[0112] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A lithium-rich manganese-based cathode material, characterized in that, The chemical formula of the lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiMO2, where M is selected from Ni, Mn, Co, Cr or Fe; 0 < x ≤ 1; The lithium-rich manganese-based cathode material has a spinel interface, and the lithium-rich manganese-based cathode material contains both a rhombic LiMO2 structure and a monoclinic Li2MnO3 structure; The preparation of the lithium-rich manganese-based cathode material includes the following steps: A mixed material of a lithium-rich manganese-based cathode material precursor and a lithium source is heat-insulated in an oxygen-containing atmosphere in a first low-temperature zone to decompose the mixed material; Subsequently, it is heat-insulated in a high-temperature zone to generate a lithium-rich manganese-based material containing both a trigonal layered structure and a monoclinic layered structure; the oxygen-containing atmosphere is adjusted to an oxygen-free atmosphere, and the surface of the lithium-rich manganese-based material is in a lithium-deficient state under a slightly positive pressure condition; Then, it is heat-insulated in an oxygen-containing atmosphere in a second low-temperature zone to obtain a lithium-rich manganese-based cathode material with an in-situ constructed spinel interface; The temperature of the first low-temperature zone is 480 - 550 °C, the temperature of the high-temperature zone is 800 - 1000 °C, and the temperature of the second low-temperature zone is 550 - 750 °C.

2. A method for preparing a lithium-rich manganese-based cathode material as described in claim 1, characterized in that, Including the following steps: A mixed material of a lithium-rich manganese-based cathode material precursor and a lithium source is heat-insulated in an oxygen-containing atmosphere in a first low-temperature zone to decompose the mixed material; Subsequently, it is heat-insulated in a high-temperature zone to generate a lithium-rich manganese-based material containing both a trigonal layered structure and a monoclinic layered structure; the oxygen-containing atmosphere is adjusted to an oxygen-free atmosphere, and the surface of the lithium-rich manganese-based material is in a lithium-deficient state under a slightly positive pressure condition; Then, it is heat-insulated in an oxygen-containing atmosphere in a second low-temperature zone to obtain a lithium-rich manganese-based cathode material with an in-situ constructed spinel interface; The temperature of the first low-temperature zone is 480 - 550 °C, the temperature of the high-temperature zone is 800 - 1000 °C, and the temperature of the second low-temperature zone is 550 - 750 °C.

3. The preparation method according to claim 2, characterized in that, The mass ratio of the lithium-rich manganese-based cathode material precursor to the lithium source is 2:0.8 - 1.

2.

4. The preparation method according to claim 3, characterized in that, The lithium-rich manganese-based cathode material precursor is a precursor in the form of a hydroxide or a precursor in the form of a carbonate.

5. The preparation method according to claim 3, characterized in that, The lithium-rich manganese-based cathode material precursor is particles with a particle size of 1 - 15 μm.

6. The preparation method according to claim 2, characterized in that, The heat-insulation time in the first low-temperature zone is 1 - 15 h.

7. The preparation method according to claim 2, characterized in that, The heat-insulation time in the high-temperature zone is 1 - 15 h.

8. The preparation method according to claim 2, characterized in that, The pressure condition corresponding to the slightly positive pressure is 1 - 20 Pa, and / or the holding time of the slightly positive pressure is 30 min - 7 h.

9. The preparation method according to claim 2, characterized in that, The heat-insulation time in the second low-temperature zone is 1 - 8 h.

10. The preparation method according to claim 2, characterized in that, Each oxygen-containing atmosphere is provided by air and / or oxygen.

11. The preparation method according to claim 10, characterized in that, The flow rate of air and / or oxygen is greater than 0 m 3 / h and ≤ 10 m 3 / h.

12. The preparation method according to claim 2, characterized in that, The oxygen-free atmosphere is provided by nitrogen and / or inert gas.

13. The preparation method according to claim 12, characterized in that, The flow rate of nitrogen and / or inert gas is greater than 0 m 3 / h and ≤ 10 m 3 / h.

14. The preparation method according to claim 2, characterized in that, The cooling rate from the high-temperature zone to the second low-temperature zone is 1 - 5 °C / min.

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