A high-stability lithium-rich manganese-based positive electrode material, a preparation method and use thereof

Abstract

The application provides a high-stability lithium-rich manganese-based positive electrode material and a preparation method and use thereof. The preparation method comprises the following steps: mixing a modified lithium-rich manganese-based positive electrode material and a transition metal-containing ammonium salt, sintering, and obtaining an intermediate material; and performing water immersion treatment on the intermediate material to obtain the high-stability lithium-rich manganese-based positive electrode material. The preparation method provided by the application simultaneously completes oxygen vacancy, transition metal doping and lithium concentration gradient distribution 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, inhibits voltage attenuation and has excellent long-term cycle stability, and the method is simple, low in cost, good in repeatability, very suitable for large-scale production and promoting the practical application of high-capacity and high-voltage materials in high-energy-density batteries.

Description

Technical Field

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

[0002] As an energy storage device, lithium ion batteries have the advantages of small self-discharge, long cycle life, high specific energy, environmental protection, etc., and have been widely used in the field of 3C products. However, commercial lithium ion batteries are restricted by the embedded energy storage mechanism of their own materials, and their actual energy density increases slowly and gradually approaches the limit value of 300 Wh / kg. -1 ; Therefore, in order to meet the consumption demands of the electric vehicle market, developing secondary batteries with higher energy density has become a social consensus. In recent years, lithium-rich manganese-based cathode materials, such as xLi2MnO3·(1-x)LiMO2 (0 < x < 1, M = Mn, Ni, Co), have attracted much attention due to their outstanding discharge specific capacity (up to 300 mAh / g) -1 ) and high working voltage (>4.5V).

[0003] However, lithium-rich manganese-based cathode materials have problems such as low first-cycle Coulomb efficiency, poor cycle stability and rate performance, which are related to the characteristics of oxygen release during the first-cycle charging process of this cathode material, poor stability of the cathode / electrolyte interface, and poor electronic / ionic conductivity of itself. Under the high-voltage charging state above 4.5V in the first cycle, oxygen atoms in the lattice are removed, forming a large number of oxygen vacancies. Transition metal ions migrate, causing the crystal structure to rearrange. The reinsertion of lithium ions is hindered, and the oxygen molecules formed inside the grains are released in the form of oxygen, resulting in irreversible capacity loss. Therefore, the first-cycle discharge capacity is reduced; during the anion redox process with a charging voltage higher than 4.5V, capacity / voltage decay occurs during cycling due to unwanted phase changes; during the charge-discharge cycle process of the material, the side reactions at the cathode / electrolyte interface are intensified, especially the surface structure of the material deteriorates, resulting in a gradual decrease in capacity; the composition phase Li2MnO3 of the lithium-rich manganese-based cathode material has electrical insulation characteristics, and the lithium ion diffusion channels are restricted. Especially, the side reaction products on the surface of the cathode material and the electrolyte seriously hinder the transmission of lithium ions and electrons at the interface, resulting in an increase in impedance under high current.

[0004] Therefore, how to improve the electrochemical performance of lithium-rich manganese-based cathode materials is a technical problem that亟待解决的技术问题. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a highly stable lithium-rich manganese-based cathode material, its preparation method, and its applications. The preparation method provided by this invention simultaneously achieves oxygen vacancies, transition metal doping, and lithium concentration gradient distribution on the surface of the lithium-rich manganese-based cathode material, thereby realizing the high rate performance, suppressed voltage decay, and excellent long-term cycle stability of the lithium-rich manganese-based cathode material. Furthermore, the method is simple, low-cost, and highly reproducible, making it very suitable for large-scale production and promoting the practical application of high-capacity, high-voltage materials in high-energy-density batteries.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a highly stable lithium-rich manganese-based cathode material, the method comprising the following steps:

[0008] The lithium-rich manganese-based cathode material to be modified and an ammonium salt containing a transition metal are mixed and sintered to obtain an intermediate material.

[0009] The intermediate material was subjected to water immersion treatment to obtain the highly stable lithium-rich manganese-based cathode material.

[0010] The lithium-rich manganese-based cathode material to be modified in this invention is either the product obtained by calcining the precursor material and the lithium source once, or the product obtained by calcining once using a solid-state sintering method; thus, the method for preparing the lithium-rich manganese-based cathode material is applicable to this invention.

[0011] The preparation method provided by this invention uses an ammonium salt containing a transition metal to treat the modified lithium-rich manganese-based cathode material. After sintering, a one-step method is used to achieve transition metal doping, surface oxygen vacancies, and water-soluble transition metal lithium salt coating (intermediate material) in the lithium-rich manganese-based cathode material. Further, a subsequent water immersion treatment washes away the water-soluble transition metal lithium salt, forming a protective layer with a lithium concentration gradient distribution. This protective layer can effectively stabilize the electrode / electrolyte interface. Furthermore, this protective layer can suppress the phase transition from layered structure to spinel structure, significantly improving the thermal stability of the structure. Thus, the lithium-rich manganese-based cathode material achieves high rate performance, suppressed voltage decay, and excellent long-cycle stability. The method is simple, low-cost, and highly reproducible, making it very suitable for large-scale production and promoting the practical application of high-capacity, high-voltage materials in high-energy-density batteries. This opens a new avenue for solving the interface problem of lithium-ion battery cathode materials, promoting the practical application of high-capacity, high-voltage materials in high-energy-density batteries.

[0012] In this invention, if the ammonium salt containing transition metals is not treated and instead a pure ammonium salt is used, a gradient distribution of lithium concentration cannot be achieved even after subsequent water immersion treatment. Furthermore, if the transition metal is a non-ammonium salt, oxygen vacancies cannot be obtained. At the same time, if the obtained transition metal lithium salt is poorly soluble in water, it is also not conducive to the preparation of lithium-rich manganese-based materials with a gradient distribution of lithium concentration. In other words, this invention achieves the formation of a protective layer with oxygen vacancies, transition metal doping, and a gradient distribution of lithium concentration simultaneously through a specific modification and sintering treatment of the transition metal ammonium salt, in conjunction with a simple subsequent water immersion process.

[0013] Preferably, the preparation of the lithium-rich manganese-based cathode material to be modified includes:

[0014] The lithium-rich manganese-based precursor material was mixed with a lithium source and calcined to obtain the lithium-rich manganese-based cathode material to be modified.

[0015] Preferably, the lithium-rich manganese-based precursor material includes manganese and non-manganese transition metal elements.

[0016] Preferably, the non-manganese transition metal element includes Ni and / or Co.

[0017] It should be noted that the lithium-rich manganese-based precursor materials provided by this invention include hydroxide precursor materials, carbonate precursor materials, or precursor materials prepared by the sol-gel method, etc., that is, conventional lithium-rich manganese-based precursor material types that can be paired with a lithium source, and this invention applies to all of them.

[0018] For example, the present invention provides a lithium-rich manganese-based precursor material Ni x Co y Mn 1-x-y (OH)2, 0.3 < x ≤ 0.4, for example 0.33, 0.034, 0.35, 0.36, 0.38 or 0.4, etc., y ≤ 0.1, that is, 0, 0.025, 0.05, 0.075 or 0.1, etc., and its preparation method is the conventional co-precipitation method. That is, the lithium-rich manganese-based precursor material provided by the present invention is more suitable for cobalt-free or low-cobalt structures.

[0019] It should also be noted that the lithium-rich manganese-based precursor materials provided above are merely illustrative examples, and other precursor material types applicable to this invention are also applicable to this invention.

[0020] Preferably, the ratio of the total molar amount of metal elements in the lithium-rich manganese-based precursor material to the molar amount of lithium in the lithium source is 1:(1.3 to 1.6), such as 1:1.3, 1:1.35, 1:1.4, 1:1.45, 1:1.5, 1:1.55 or 1:1.6, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, the lithium-rich manganese-based precursor material is first pre-sintered and then mixed with a lithium source.

[0022] Preferably, the pre-sintering temperature is 400-600℃, such as 400℃, 450℃, 500℃, 550℃ or 600℃.

[0023] Preferably, the pre-sintering time is 3 to 6 hours, such as 3 hours, 4 hours, 5 hours or 6 hours.

[0024] Preferably, the calcination temperature is 800–1000°C, such as 800°C, 850°C, 900°C, 950°C, or 1000°C, and other unlisted values ​​within this range are also applicable.

[0025] Preferably, the calcination time is 10 to 14 hours, such as 10 hours, 11 hours, 12 hours, 13 hours or 14 hours, and other unlisted values ​​within this range are also applicable.

[0026] In this invention, pre-sintering treatment can be omitted, and the mixture can be directly calcined after mixing with the lithium source; calcination can also be carried out in stages, and the appropriate selection and adjustment can be made according to actual needs.

[0027] Preferably, the ammonium salt containing a transition metal includes any one or a combination of at least two of ammonium molybdate, ammonium tungstate, or ferric ammonium oxalate, and preferably includes at least ammonium molybdate.

[0028] In this invention, when the ammonium salt containing transition metals includes ammonium molybdate, after sintering, oxygen vacancies, molybdenum doping, and water-soluble lithium molybdate can be obtained simultaneously. Thus, after subsequent water immersion treatment, a surface protective layer with a lithium concentration gradient distribution can be obtained.

[0029] Preferably, the amount of the ammonium salt containing the transition metal added is 2 to 8 wt% of the mass of the lithium-rich manganese-based cathode material to be modified, such as 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, or 8 wt%, etc. Other unlisted values ​​within this range are also applicable.

[0030] In this invention, if the amount of ammonium salt containing transition metal is too small, it will not be conducive to the construction of lithium concentration gradient; if it is too large, it will lead to a large amount of non-chemically active metal doping, which will affect the performance of electrochemical properties.

[0031] Preferably, the sintering atmosphere includes a protective atmosphere.

[0032] Preferably, the sintering temperature is 300-500℃, such as 300℃, 325℃, 350℃, 375℃, 400℃, 425℃, 450℃, 475℃ or 500℃, and other unlisted values ​​within this range are also applicable.

[0033] In this invention, if the temperature of adding ammonium salt containing transition metal for sintering is too low, it will be difficult to achieve a full reaction between the metal and the Li source to form a Li-containing metal salt; while if the temperature is too high, it will cause secondary sintering of the lithium-rich manganese cathode, which is not conducive to the diffusion of Li ions.

[0034] Preferably, the sintering time is 2 to 6 hours, such as 2 hours, 3 hours, 4 hours, 5 hours or 6 hours, and other unlisted values ​​within this range are also applicable.

[0035] Preferably, the water immersion treatment includes placing the intermediate material in an aqueous solution and subjecting it to ultrasonic treatment.

[0036] In this invention, ultrasonic water immersion can better dissolve the Li-containing metal salt on the surface of lithium-rich manganese, thereby constructing a protective layer with a Li concentration gradient distribution.

[0037] Preferably, the solid-liquid ratio of the water to the intermediate material is 1:1 to 1:4, such as 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5 or 1:1.4, etc. Other unlisted values ​​within this range are also applicable.

[0038] In this invention, if the solid-liquid ratio is too small, that is, too little positive electrode material is added, excessive delithiation will occur, which will increase the lithium defects on the surface and is not conducive to the stability of the material structure. On the other hand, if the solid-liquid ratio is too large, that is, too much positive electrode material is added, it is not conducive to the formation of a protective layer with a lithium concentration gradient distribution on the surface.

[0039] Preferably, the ultrasound duration is 0.5 to 2 hours, such as 0.5 hours, 1 hour, 1.5 hours, or 2 hours. Other values ​​not listed within this range are also applicable.

[0040] As a preferred technical solution, the preparation method includes the following steps:

[0041] The lithium-rich manganese-based precursor material is pre-sintered at 400–600 °C for 3–6 h, and then mixed with a lithium source. The ratio of the total molar amount of metal elements in the lithium-rich manganese-based precursor material to the molar amount of lithium in the lithium source is 1:(1.3–1.6). Then it is calcined at 800–1000 °C for 10–14 h to obtain the lithium-rich manganese-based cathode material to be modified.

[0042] The lithium-rich manganese-based cathode material to be modified and an ammonium salt containing a transition metal are mixed. The amount of the ammonium salt containing the transition metal is 2 to 8 wt% of the mass of the lithium-rich manganese-based cathode material to be modified. The mixture is sintered at 300 to 500 °C for 2 to 6 h under a protective atmosphere to obtain an intermediate material.

[0043] The intermediate material was placed in an aqueous solution at a solid-liquid ratio of 1:1 to 1:4 and subjected to ultrasonic treatment for 0.5 to 2 hours to obtain the highly stable lithium-rich manganese-based cathode material.

[0044] The ammonium salt containing transition metals includes at least ammonium molybdate.

[0045] In a second aspect, the present invention provides a highly stable lithium-rich manganese-based cathode material, wherein the highly stable lithium-rich manganese-based cathode material is prepared by the preparation method described in the first aspect.

[0046] Thirdly, the present invention also provides a lithium-ion battery comprising a highly stable lithium-rich manganese-based cathode material as described in the second aspect.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The preparation method provided by this invention uses an ammonium salt containing a transition metal to treat the modified lithium-rich manganese-based cathode material. After sintering, transition metal doping, surface oxygen vacancies, and water-soluble transition metal lithium salt coating (intermediate material) are achieved in one step in the lithium-rich manganese-based cathode material. Further water immersion treatment removes the water-soluble transition metal lithium salt, forming a protective layer with a lithium concentration gradient distribution. This protective layer effectively stabilizes the electrode / electrolyte interface and suppresses the phase transition from layered structure to spinel structure, significantly improving the thermal stability of the structure. This achieves the goal of high rate performance, suppressed voltage decay, and excellent long-term cycle stability in the lithium-rich manganese-based cathode material. The method is simple, low-cost, and highly reproducible, making it very suitable for large-scale production and promoting the practical application of high-capacity, high-voltage materials in high-energy-density batteries. It opens a new avenue for solving the interface problem of lithium-ion battery cathode materials, further promoting the practical application of high-capacity, high-voltage materials in high-energy-density batteries. Detailed Implementation

[0049] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are merely illustrative of the present invention and should not be construed as limiting the invention.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms “comprising” and “having” and any variations thereof in this application are intended to cover non-exclusive inclusion.

[0051] In the description of this application, the technical terms "first," "second," etc., are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order, or primary and secondary relationship of the indicated technical features.

[0052] In one specific embodiment, the present invention provides a method for preparing a lithium-rich manganese-based precursor material, the method comprising:

[0053] A 2 mol / L manganese-based mixed salt solution, a 2 mol / L sodium hydroxide solution, and a 0.1 mol / L oxalic acid solution were added concurrently to the bottom liquid of the reactor (water, sodium hydroxide, and oxalic acid solutions were used as the bottom liquid, with a pH of 11.5–11.8 and an oxalic acid concentration of 0.01 mol / L). N2 was introduced, and the temperature was controlled at 58°C. The mixture was continuously stirred at 350 r / min, maintaining the pH of the reaction system at 9.0–9.5 for co-precipitation. After washing, drying, and sieving, Ni was obtained. x Co y Mn 1-x-y (OH)2, 0.3 < x ≤ 0.4, y ≤ 0.1 lithium-rich manganese-based precursor material.

[0054] The lithium-rich manganese-based precursor materials in the following examples and comparative examples were all prepared using the specific embodiments described above.

[0055] Example 1

[0056] This embodiment provides a lithium-rich manganese-based cathode material with oxygen vacancy surface modification, molybdenum doping, and a lithium concentration gradient distribution protective layer; the preparation method of the lithium-rich manganese-based cathode material is as follows.

[0057] (1) The lithium-rich manganese precursor (Ni 0.40 Mn 0.60 (OH)2) was placed in a muffle furnace and pre-calcined at 500℃ for 5h. Then it was weighed and mixed with lithium carbonate at a ratio of lithium to transition metal molar ratio of 1.4. Then it was calcined at 900℃ for 12h and cooled naturally to obtain the lithium-rich manganese-based cathode material to be modified.

[0058] (2) The above-obtained lithium-rich manganese cathode material to be modified is uniformly mixed with 4 wt% ammonium molybdate (the amount added is 4 wt% of the mass of the lithium-rich manganese cathode material to be modified). The mixed sample is placed in a tube furnace and sintered at 400°C for 4 h under an argon atmosphere to prepare a lithium-rich manganese-based cathode material (intermediate material) with oxygen vacancies, molybdenum doping and lithium molybdate coating.

[0059] (3) The lithium-rich manganese-based cathode material with molybdenum doping and lithium molybdate coating obtained above is ultrasonicated with a certain mass of pure water for 1 hour. At this time, the solid-liquid ratio is 1:1. After drying, a lithium-rich manganese-based cathode material with oxygen vacancy surface modification, molybdenum doping and lithium concentration gradient distribution protective layer is obtained.

[0060] Example 2

[0061] This embodiment provides a lithium-rich manganese-based cathode material with oxygen vacancy surface modification, molybdenum doping, and a lithium concentration gradient distribution protective layer; the preparation method of the lithium-rich manganese-based cathode material is as follows.

[0062] (1) The lithium-rich manganese precursor (Ni 0.40 Mn 0.60 (OH)2) was placed in a muffle furnace and pre-calcined at 500℃ for 5h. Then it was weighed and mixed with lithium carbonate at a ratio of lithium to transition metal molar ratio of 1.4. Then it was calcined at 900℃ for 12h and cooled naturally to obtain the lithium-rich manganese-based cathode material to be modified.

[0063] (2) The above-obtained lithium-rich manganese cathode material to be modified is uniformly mixed with 8 wt% ammonium molybdate (the amount added is 8 wt% of the mass of the lithium-rich manganese cathode material to be modified). The mixed sample is placed in a tube furnace and sintered at 400°C for 4 h under an argon atmosphere to prepare a lithium-rich manganese-based cathode material (intermediate material) with oxygen vacancies, molybdenum doping and lithium molybdate coating.

[0064] (3) The lithium-rich manganese-based cathode material with molybdenum doping and lithium molybdate coating obtained above is ultrasonicated with a certain mass of pure water for 1 hour. At this time, the solid-liquid ratio is 1:2. After drying, a lithium-rich manganese-based cathode material with oxygen vacancy surface modification, molybdenum doping and lithium concentration gradient distribution protective layer is obtained.

[0065] Example 3

[0066] This embodiment provides a lithium-rich manganese-based cathode material with oxygen vacancy surface modification, molybdenum doping, and a lithium concentration gradient distribution protective layer; the preparation method of the lithium-rich manganese-based cathode material is as follows.

[0067] (1) The lithium-rich manganese precursor (Ni 0.40 Mn 0.60(OH)2) was placed in a muffle furnace and pre-calcined at 500℃ for 5h. Then it was weighed and mixed evenly with lithium carbonate at a lithium to transition metal molar ratio of 1.4. Then it was calcined at 800℃ for 14h and cooled naturally to obtain the lithium-rich manganese-based cathode material to be modified.

[0068] (2) The above-obtained lithium-rich manganese cathode material to be modified is uniformly mixed with 2wt% ammonium molybdate (the amount added is 2wt% of the mass of the lithium-rich manganese cathode material to be modified), and the mixed sample is placed in a tube furnace and sintered at 300°C for 6 hours under an argon atmosphere to prepare a lithium-rich manganese-based cathode material (intermediate material) with oxygen vacancies, molybdenum doping and lithium molybdate coating.

[0069] (3) The lithium-rich manganese-based cathode material with molybdenum doping and lithium molybdate coating obtained above is ultrasonicated with a certain mass of pure water for 0.5 h. At this time, the solid-liquid ratio is 1:3. After drying, a lithium-rich manganese-based cathode material with oxygen vacancy surface modification, molybdenum doping and lithium concentration gradient distribution protective layer is obtained.

[0070] Example 4

[0071] This embodiment provides a lithium-rich manganese-based cathode material with oxygen vacancy surface modification, molybdenum doping, and a lithium concentration gradient distribution protective layer; the preparation method of the lithium-rich manganese-based cathode material is as follows.

[0072] (1) The lithium-rich manganese precursor (Ni 0.40 Mn 0.60 (OH)2) was placed in a muffle furnace and pre-calcined at 500℃ for 5h (first calcination). Then it was weighed and mixed with lithium carbonate at a ratio of lithium to transition metal molar ratio of 1.4. Then it was calcined at 900℃ for 12h (second calcination). After natural cooling, the lithium-rich manganese-based cathode material to be modified was obtained.

[0073] (2) The above-obtained lithium-rich manganese cathode material to be modified is uniformly mixed with 4 wt% ammonium molybdate (the amount added is 4 wt% of the mass of the lithium-rich manganese cathode material to be modified). The mixed sample is placed in a tube furnace and sintered at 400°C for 4 h under an argon atmosphere to prepare a lithium-rich manganese-based cathode material (intermediate material) with oxygen vacancies, molybdenum doping and lithium molybdate coating.

[0074] (3) The lithium-rich manganese-based cathode material with molybdenum doping and lithium molybdate coating obtained above is ultrasonicated with a certain mass of pure water for 1 hour. At this time, the solid-liquid ratio is 1:4. After drying, a lithium-rich manganese-based cathode material with oxygen vacancy surface modification, molybdenum doping and lithium concentration gradient distribution protective layer is obtained.

[0075] Example 5

[0076] The difference between this embodiment and Embodiment 1 is that the lithium-rich manganese precursor in step (1) of this embodiment is Ni. 0.35 Co 0.05 Mn 0.60 (OH)2.

[0077] The remaining preparation methods and parameters are consistent with those in Example 1.

[0078] Example 6

[0079] The difference between this embodiment and embodiment 1 is that ammonium tungstate is used instead of ammonium molybdate in step (2) of this embodiment.

[0080] The remaining preparation methods and parameters are consistent with those in Example 1.

[0081] Example 7

[0082] The difference between this embodiment and embodiment 1 is that the amount of ammonium molybdate added in step (2) of this embodiment is 1 wt%.

[0083] The remaining preparation methods and parameters are consistent with those in Example 1.

[0084] Example 8

[0085] The difference between this embodiment and embodiment 1 is that the amount of ammonium molybdate added in step (2) of this embodiment is 10 wt%.

[0086] The remaining preparation methods and parameters are consistent with those in Example 1.

[0087] Example 9

[0088] The difference between this embodiment and embodiment 1 is that the sintering temperature in step (2) of this embodiment is 200℃.

[0089] The remaining preparation methods and parameters are consistent with those in Example 1.

[0090] Example 10

[0091] The difference between this embodiment and embodiment 1 is that the sintering temperature in step (2) of this embodiment is 600℃.

[0092] The remaining preparation methods and parameters are consistent with those in Example 1.

[0093] Example 11

[0094] The difference between this embodiment and embodiment 1 is that in step (3) of this embodiment, water immersion treatment is carried out by stirring.

[0095] The remaining preparation methods and parameters are consistent with those in Example 1.

[0096] Example 12

[0097] The difference between this embodiment and embodiment 1 is that the solid-liquid ratio in step (3) of this embodiment is 1:0.5.

[0098] The remaining preparation methods and parameters are consistent with those in Example 1.

[0099] Example 13

[0100] The difference between this embodiment and embodiment 1 is that the solid-liquid ratio in step (3) of this embodiment is 1:5.

[0101] The remaining preparation methods and parameters are consistent with those in Example 1.

[0102] Comparative Example 1

[0103] The difference between this comparative example and Example 1 is that the lithium-rich manganese-based cathode material in this comparative example is the same lithium-rich manganese-based cathode material to be modified in Example 1.

[0104] In the preparation method, only step (1) is performed.

[0105] The remaining preparation methods and parameters are consistent with those in Example 1.

[0106] Comparative Example 2

[0107] The difference between this comparative example and Example 1 is that in the preparation method of this comparative example, only steps (1) and (2) are performed.

[0108] The remaining preparation methods and parameters are consistent with those in Example 1.

[0109] The conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) of the lithium-rich manganese-based cathode materials prepared in Examples 1-13 and Comparative Examples 1-3 were weighed at a mass ratio of 8:1:1 and dissolved in N-methylpyrrolidone (NMP) and mixed thoroughly. Then, the slurry was coated onto aluminum foil using a coater and dried in a vacuum drying oven at 80°C for 8 hours. Finally, the aluminum foil was stamped into 1.13 cm thick sheets. 2 A circular positive electrode sheet was obtained. Using the resulting electrode sheet as the positive electrode and a lithium metal sheet as the counter electrode, a porous polypropylene membrane (Celgard 2400, USA) was used as a separator to separate the positive and counter electrodes. The CR2032 button cell was assembled in an argon-filled glove box. Cyclic performance tests were conducted using a battery testing system (Blue Electric CT2001A, Wuhan, China) at rates of 0.1C and 0.33C under conditions ranging from 2.5V to 4.55V. The test results are shown in Table 1.

[0110] Table 1

[0111]

[0112]

[0113] From Table 1, we can obtain:

[0114] The data from Examples 1 and 6 show that when ammonium salts other than ammonium molybdate are used, lithium salts that are insoluble in water will appear, thus making it impossible to prepare a lithium concentration gradient protective layer.

[0115] The data from Examples 1, 7, and 8 show that if the amount of ammonium salt containing transition metal is too small, the performance will decrease; while if the amount is too large, the performance will decrease further.

[0116] The data from Examples 1, 9, and 10 show that if the sintering temperature after adding ammonium salt is too low, it will not be conducive to the formation of lithium salt; while if the sintering temperature is too high, the surface temperature of the material will be too high, which will cause changes in the surface structure of the material and will not be conducive to the utilization of capacity.

[0117] The data from Examples 1 and 11 show that using a non-ultrasonic water immersion method slows down the lithium dissolution rate and fails to completely prepare a protective layer with a lithium concentration gradient.

[0118] The data results from Examples 1, 12, and 13 show that an excessively high solid-liquid ratio, i.e., too much cathode material, will result in a smaller amount of lithium dissolution, while an excessively low solid-liquid ratio, i.e., too little cathode material, will lead to the dissolution of other elements in the cathode material.

[0119] The data from Example 1 and Comparative Examples 1 and 2 show that without subsequent treatment with transition metal ammonium salts or without water immersion treatment, it is impossible to simultaneously achieve a protective layer with oxygen vacancies, transition metal doping, and lithium concentration gradient distribution.

[0120] In summary, the preparation method provided by this invention uses an ammonium salt containing a transition metal to treat the modified lithium-rich manganese-based cathode material. After sintering, transition metal doping, surface oxygen vacancies, and water-soluble transition metal lithium salt coating (intermediate material) are achieved in one step in the lithium-rich manganese-based cathode material. Further water immersion washing removes the water-soluble transition metal lithium salt, forming a protective layer with a lithium concentration gradient. This protective layer effectively stabilizes the electrode / electrolyte interface and suppresses the phase transition from layered to spinel structure, significantly improving the thermal stability of the structure. This achieves the goal of high rate performance, suppressed voltage decay, and excellent long-term cycle stability in the lithium-rich manganese-based cathode material. The method is simple, low-cost, and highly reproducible, making it very suitable for large-scale production and promoting the practical application of high-capacity, high-voltage materials in high-energy-density batteries. It opens a new avenue for solving the interface problem of lithium-ion battery cathode materials, further promoting the practical application of high-capacity, high-voltage materials in high-energy-density batteries.

[0121] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a highly stable lithium-rich manganese-based cathode material, characterized in that, The preparation method includes the following steps: The lithium-rich manganese-based cathode material to be modified and an ammonium salt containing a transition metal are mixed and sintered to obtain an intermediate material. The intermediate material was subjected to water immersion treatment to obtain the highly stable lithium-rich manganese-based cathode material; The amount of the ammonium salt containing the transition metal added is 2-8 wt% of the mass of the lithium-rich manganese-based cathode material to be modified. The water immersion treatment includes placing the intermediate material in an aqueous solution and subjecting it to ultrasonic treatment; The solid-liquid ratio of the water to the intermediate material is 1:1 to 1:4; The ammonium salt containing the transition metal is ammonium molybdate; The sintering temperature is 300~500℃.

2. The preparation method according to claim 1, characterized in that, The preparation of the lithium-rich manganese-based cathode material to be modified includes: The lithium-rich manganese-based precursor material was mixed with a lithium source and calcined to obtain the lithium-rich manganese-based cathode material to be modified.

3. The preparation method according to claim 2, characterized in that, The lithium-rich manganese-based precursor material includes manganese and non-manganese transition metal elements.

4. The preparation method according to claim 3, characterized in that, The non-manganese transition metal elements include Ni and / or Co.

5. The preparation method according to claim 2, characterized in that, The ratio of the total molar amount of metal elements in the lithium-rich manganese-based precursor material to the molar amount of lithium in the lithium source is 1:(1.3~1.6).

6. The preparation method according to claim 2, characterized in that, The lithium-rich manganese-based precursor material is first pre-sintered and then mixed with a lithium source.

7. The preparation method according to claim 6, characterized in that, The pre-sintering temperature is 400~600℃.

8. The preparation method according to claim 6, characterized in that, The pre-sintering time is 3-6 hours.

9. The preparation method according to claim 2, characterized in that, The calcination temperature is 800~1000℃.

10. The preparation method according to claim 2, characterized in that, The calcination time is 10-14 hours.

11. The preparation method according to claim 1, characterized in that, The sintering atmosphere includes a protective atmosphere.

12. The preparation method according to claim 1, characterized in that, The sintering time is 2 to 6 hours.

13. The preparation method according to claim 1, characterized in that, The duration of the ultrasound is 0.5 to 2 hours.

14. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: The lithium-rich manganese-based precursor material is pre-sintered at 400~600℃ for 3~6h, and then mixed with a lithium source. The ratio of the total molar amount of metal elements in the lithium-rich manganese-based precursor material to the molar amount of lithium in the lithium source is 1:(1.3~1.6). Then it is calcined at 800~1000℃ for 10~14h to obtain the lithium-rich manganese-based cathode material to be modified. The lithium-rich manganese-based cathode material to be modified and an ammonium salt containing a transition metal are mixed. The amount of the ammonium salt containing the transition metal is 2-8 wt% of the mass of the lithium-rich manganese-based cathode material to be modified. The mixture is sintered at 300-500℃ for 2-6 h under a protective atmosphere to obtain an intermediate material. The intermediate material was placed in an aqueous solution at a solid-liquid ratio of 1:1 to 1:4 and subjected to ultrasonic treatment for 0.5 to 2 hours to obtain the highly stable lithium-rich manganese-based cathode material. The ammonium salt containing the transition metal is ammonium molybdate.

15. A highly stable lithium-rich manganese-based cathode material, characterized in that, The highly stable lithium-rich manganese-based cathode material is prepared by the preparation method described in any one of claims 1-14.

16. A lithium-ion battery, characterized in that, The lithium-ion battery includes the highly stable lithium-rich manganese-based cathode material as described in claim 15.

Images