Lithium-rich manganese-based positive electrode material and preparation method thereof, electrode sheet and lithium-ion battery

Abstract

The present application discloses a method for preparing a lithium-rich manganese-based positive electrode material, which includes adding an M-based metal-organic framework material during the precursor formation process, inducing the generation and growth of a micron-rod-shaped precursor on the surface of the M-based metal-organic framework material, and then sintering the M-based metal-organic framework material to dissociate and collapse, forming a micron-hollow rod-shaped lithium-rich manganese-based positive electrode material, where M includes at least one metal element. The micron-hollow rod-shaped lithium-rich manganese-based positive electrode material prepared by this method can release the stress caused by the expansion and contraction of the lattice during the charge and discharge process due to the hollow structure, thereby releasing the accumulation of stress during the charge and discharge cycle and effectively improving the cycle stability. Moreover, at high temperatures, the M metal clusters migrate to the bulk phase of the positive electrode material, realizing the gradient doping of the M element, which significantly improves the discharge specific capacity and cycle stability of the positive electrode material.

Description

Technical Field

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

[0002] With the rapid advancement of society and the accelerated advancement of economic development, energy storage devices have garnered increasing attention. As a widely used energy storage device, lithium-ion batteries hold an irreplaceable position in today's electronics and automotive industries. Compared to traditional nickel-metal hydride, lead-acid, and nickel-cadmium batteries, lithium-ion batteries offer numerous advantages, including high energy density, high operating voltage, and excellent cycle stability. Since their commercial launch in the 1990s, lithium-ion batteries have been used in various electronic products over the past few decades. As power components, they have also fueled the rapid development of new energy vehicles in recent years.

[0003] Lithium-ion battery cathode materials are the key factor restricting the improvement of the energy density of the whole battery. As the earliest discovered lithium-ion battery cathode material, LiCoO2 still has certain application areas. Although LiCoO2 technology is mature and has good cycle performance, its energy density is low, and limited and expensive cobalt resources have pushed up its manufacturing costs. In addition, its safety issues under high voltage have also seriously restricted its promotion and application in large-scale energy storage components and new energy vehicle power accessories. In terms of energy density, ternary lithium battery LiNi x Co y Mn 1-x-y The maximum discharge capacity of O2 and spinel lithium manganese oxide LiMn2O4 is less than 200mAh·g -1 Compared with the above-mentioned cathode materials, lithium-rich manganese-based xLi2MnO3(1–x)LiMO2(M=Ni,Co,Mn,etc.) materials have extremely high reversible specific capacity (higher than 250mAh·g -1 ) and high operating voltage (>3.5V vs.Li / Li + ), and the price of Mn element is much lower than Co, which has attracted much attention. However, the lithium-rich manganese-based material was first charged to 4.5V (vs.Li / Li + ), the activation of the Li2MnO3 phase is accompanied by irreversible Li + Deintercalation and oxygen loss lead to low coulombic efficiency in the first cycle. In subsequent cycles, cation rearrangement and continuous lattice oxygen loss lead to structural collapse, transforming from a layered phase to a spinel structure, resulting in severe capacity and median voltage decay.

[0004] At present, lithium-rich manganese-based materials are mainly prepared by coprecipitation method, sol-gel method, hydrothermal synthesis method and solid-phase synthesis method. The coprecipitation synthesis method of lithium-rich manganese-based materials is currently recognized as the mainstream synthesis method with simple process and low cost. However, the spherical lithium-rich manganese-based cathode materials prepared by this method are generally particles with a size of several micrometers. The particle size is large, the lithium ion migration path is long, the diffusion kinetic performance is poor, the capacity decay is serious, and the cycle stability and rate performance need to be further improved. Summary of the Invention

[0005] The lithium-rich manganese-based cathode material, its preparation method, electrode sheet and lithium ion battery provided by the present invention solve the problems of poor cycle stability and poor rate performance of the lithium-rich manganese-based cathode material.

[0006] In order to solve the above technical problems, the present application provides a lithium-rich manganese-based cathode material, and the lithium-rich manganese-based cathode material has a micron hollow rod-like structure.

[0007] In one embodiment, the molecular formula of the lithium-rich manganese-based cathode material is Li 1.2 (Ni 0.13 Co 0.13 Mn 0.54 ) 1-x M x O2, where the value of x is 0 < x ≤ 0.08, and M includes at least one metal element.

[0008] In one embodiment, M includes any one of chromium, nickel, iron, cobalt, copper, zinc, silver, lanthanum, manganese, palladium, tin, magnesium, titanium and platinum, or M includes at least one transition metal element. In order to solve the above technical problems, the present application provides a preparation method of a lithium-rich manganese-based cathode material, including adding an M-based metal-organic framework material during the formation of the precursor to induce the generation and growth of micron rod-like precursors on the surface of the M-based metal-organic framework material, and then sintering to dissociate and collapse the M-based metal-organic framework material to form a hollow micron rod-like lithium-rich manganese-based cathode material, where M includes at least one metal element.

[0009] In order to solve the above technical problems, the present application also provides another preparation method of a lithium-rich manganese-based cathode material, including:

[0010] Preparation of solution A: Dissolve lithium salt, nickel salt, cobalt salt and manganese salt into the first mixed solvent according to the molar ratio, and stir to obtain solution A. The first mixed solvent is a mixture of deionized water and absolute ethanol;

[0011] Preparation of solution B: Dissolve anhydrous oxalic acid into the second mixed solvent, and stir to obtain solution B. The second mixed solvent is a mixture of deionized water and absolute ethanol;

[0012] Solution C is prepared by adding TMA-M MOFs to solution B according to a molar ratio and ultrasonically dispersing the solution to obtain solution C, wherein TMA is dimethylimidazole, M includes at least one metal element, and MOFs is a metal organic framework;

[0013] To prepare the final product, solution A was added dropwise to solution C under stirring, and the mixture was evaporated, sintered, and cooled to room temperature to obtain a lithium-rich manganese-based positive electrode material.

[0014] In one embodiment, the lithium salt is at least one of lithium acetate, lithium carbonate, lithium nitrate and lithium sulfate; and / or the nickel salt is at least one of nickel acetate, nickel carbonate, nickel nitrate and nickel sulfate; and / or the cobalt salt is at least one of cobalt acetate, cobalt carbonate, cobalt nitrate and cobalt sulfate; and / or the manganese salt is at least one of manganese acetate, manganese carbonate, manganese nitrate and manganese sulfate.

[0015] In one embodiment, preferably, the volume ratio of deionized water to anhydrous ethanol in the first mixed solvent is 1:12;

[0016] Preferably, the volume ratio of deionized water to anhydrous ethanol in the second mixed solvent is 4:6.

[0017] Preferably, the stirring in the preparation of solution A is magnetic stirring, and the conditions are: magnetic stirring at a speed of 500 rpm to 1200 rpm for 10 min to 30 min;

[0018] Preferably, the stirring in the preparation of solution B is magnetic stirring, and the conditions are: magnetic stirring at a speed of 500 rpm-1200 rpm for 10 min-40 min;

[0019] Preferably, the ultrasonic dispersion conditions during the preparation of solution C are: ultrasonic dispersion for 10 min-20 min;

[0020] Preferably, the stirring during the preparation of the final product is magnetic stirring, and the conditions are: magnetic stirring at a speed of 500 rpm-1200 rpm for 4 h-12 h;

[0021] Preferably, the evaporation conditions are: evaporation in an oven at 60°C-80°C for 48h-72h;

[0022] Preferably, the sintering conditions are: sintering at 300° C.-600° C. in an air atmosphere for 1 h-10 h, and then sintering at 700° C.-1000° C. in an air atmosphere for 4 h-24 h;

[0023] Preferably, the cooling condition is: a cooling rate of 1K-20K / min.

[0024] In one embodiment, before the step of preparing solution C, the preparation of TMA-MMOFs is also included. The preparation of TMA-MMOFs includes:

[0025] M salt and TMA were dissolved in deionized water to form solution D and solution E, respectively;

[0026] Solution D was added dropwise into solution E, and TMA-M MOFs were prepared after stirring, washing, and drying.

[0027] In order to solve the above technical problems, the present application also provides an electrode sheet, which is prepared using any of the above-mentioned lithium-rich manganese-based positive electrode materials.

[0028] In order to solve the above technical problems, the present application also provides a lithium-ion battery prepared using any of the electrode sheets mentioned above.

[0029] The preparation method of the lithium-rich manganese-based positive electrode material of the present invention is based on the oxalic acid co-precipitation method. By adding M-based metal-organic framework material (M-MOFs) nucleation particles, micron-rod-shaped precursors are induced to form and grow on the MOFs surface. During the high-temperature sintering process, the M-MOFs dissociate and collapse to form hollow micron-rod-shaped lithium-rich manganese-based positive electrode materials. Because the hollow structure can release the stress caused by lattice expansion and contraction during the charge and discharge process compared to the solid structure, the accumulated stress during the charge and discharge cycle is released, effectively improving the cycle stability. In addition, at high temperatures, the M metal clusters migrate to the bulk of the positive electrode material, realizing the gradient doping of the M element. During the charge and discharge process, the M element can preferentially migrate, inhibiting the migration and dissolution of active transition metal ions on the surface of the positive electrode material, thereby significantly improving the discharge specific capacity and cycle stability of the positive electrode material. The fully exposed {010} crystal planes of the lithium-rich manganese-based positive electrode material shorten the Li ion diffusion path of the material system, ensuring that the cycle stability of the lithium-rich manganese-based positive electrode material is significantly improved without compromising the rate performance of the lithium-rich manganese-based positive electrode material. In addition, this preparation method eliminates the ball milling mixing process of the Li source and the M salt precursor, simplifying the preparation steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 X-ray diffraction (XRD) patterns of the lithium-rich manganese-based positive electrode materials prepared in Examples 1-4 of the present invention and the lithium-rich manganese-based positive electrode materials prepared in the comparative example;

[0031] Figure 2 This is a scanning electron microscope (SEM) image of the TMA-Cr MOFs added in Examples 1-4 of the present invention;

[0032] Figure 3 This is a scanning electron microscope (SEM) image of the lithium-rich manganese-based positive electrode material prepared in Example 4 of the present invention;

[0033] Figure 4 This is a high-resolution transmission electron microscope (TEM) image of the lithium-rich manganese-based positive electrode material prepared in Example 4 of the present invention;

[0034] Figure 5 This is a comparison chart of the electrochemical cycle stability of the lithium-rich manganese-based positive electrode materials prepared in Examples 1-4 of the present invention and the lithium-rich manganese-based positive electrode materials prepared in the comparative example. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below by specific embodiments in conjunction with the accompanying drawings. Similar elements in different embodiments use associated similar element numbers. In the following embodiments, many detailed descriptions are intended to enable the present application to be better understood. However, those skilled in the art will readily appreciate that some of the features may be omitted under different circumstances, or may be replaced by other elements, materials, or methods. In some cases, some operations related to the present application are not shown or described in the specification. This is to avoid the core portion of the present application being overwhelmed by excessive descriptions, and for those skilled in the art, it is not necessary to describe these related operations in detail. They can fully understand the related operations based on the description in the specification and the general technical knowledge in the art.

[0036] In addition, the features, operations, or characteristics described in the specification may be combined in any appropriate manner to form various embodiments. Furthermore, the steps or actions in the method description may be reordered or adjusted in a manner readily apparent to those skilled in the art. Therefore, the various sequences in the specification and drawings are provided solely for the purpose of clearly describing a particular embodiment and are not intended to be mandatory, unless otherwise specified.

[0037] The serial numbers assigned to components herein, such as "first," "second," etc., are used solely to distinguish the objects being described and do not convey any sequential or technical meaning. References to "connection" and "coupling" herein, unless otherwise specified, include both direct and indirect connections (couplings).

[0038] As used herein, "room temperature" refers to 23±2°C.

[0039] In one embodiment, the present application provides a lithium-rich manganese-based positive electrode material that can be used in the positive electrode of a lithium-ion battery. The lithium-rich manganese-based positive electrode material is a micron hollow rod structure, and the average size of its single particles can be 1μm-10μm.

[0040] The existing spherical cathode materials prepared by the coprecipitation method for lithium-rich manganese-based cathode materials are usually large micron-sized particles with a size of about dozens of microns or hundreds of microns. The migration path of lithium ions in the cathode of lithium-ion batteries is long, and the diffusion kinetic performance is poor.

[0041] The hollow structure of the lithium-rich manganese-based cathode material of the present invention can release the stress caused by lattice expansion and contraction during charge and discharge, so the accumulation of stress in the charge and discharge cycle is released, and the cycle stability can be effectively improved. The fully exposed {010} crystal plane of the lithium-rich manganese-based cathode material can provide a fast channel for lithium ions, shortening the diffusion path of Li ions in the material system, and significantly improving the cycle stability of the lithium-rich manganese-based cathode material without compromising the rate performance of the lithium-rich manganese-based cathode material.

[0042] In one embodiment, the molecular formula of the lithium-rich manganese-based cathode material is

[0043] Li 1.2 (Ni 0.13 Co 0.13 Mn 0.54 ) 1-x M x O2, where the value of x is 0 < x ≤ 0.08, and M includes at least one metal element. In one embodiment, M includes at least one transition metal element, or M includes any one of chromium, nickel, iron, cobalt, copper, zinc, silver, lanthanum, manganese, palladium, tin, magnesium, titanium, and platinum.

[0044] More preferably, the value of x can be one of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, and 0.08.

[0045] It can be understood that during the high-temperature synthesis process, the M metal clusters migrate to the bulk phase of the cathode material, realizing the gradient doping of the M element. During the charge and discharge process, the M element can preferentially migrate, inhibiting the migration and dissolution of the active transition metal ions on the surface of the cathode material, and thus significantly improving the discharge specific capacity and cycle stability of the cathode material.

[0046] The present application also provides a preparation method for the above lithium-rich manganese-based cathode material, including:

[0047] During the formation of the precursor, an M-based metal-organic framework material is added to induce the formation and growth of micron-rod-shaped precursors on the surface of the M-based metal-organic framework material. Then, sintering is carried out to dissociate and collapse the M-based metal-organic framework material, forming a hollow micron-rod-shaped lithium-rich manganese-based cathode material, where M includes at least one metal element. In one embodiment, M includes at least one transition metal element, or M includes any one of chromium, nickel, iron, cobalt, copper, zinc, silver, lanthanum, manganese, palladium, tin, magnesium, titanium, and platinum.

[0048] The preparation method of the lithium-rich manganese-based cathode material induces the formation and growth of micron-rod precursors on the surface of the metal-organic framework material by adding M-based metal-organic framework material nucleation particles, resulting in two modification results:

[0049] 1. During the subsequent sintering process, M-MOFs dissociate and collapse to form micron-scale hollow rod-shaped lithium-rich manganese-based positive electrode materials. The fully exposed {010} crystal planes provide a fast channel for lithium ion transmission, thereby improving the material's rate performance. The presence of the hollow structure releases the stress accumulated during the cycle, giving the material excellent cycle stability.

[0050] 2. After the MOFs collapse, the M metal diffuses from the inside out, forming a gradient doping effect of the M metal. The gradient doping of the M element achieves a significant increase in the primary particles of the material. The preferential migration of the M element can inhibit the migration and dissolution of active transition metal ions on the material surface, thereby inhibiting the formation of spinel and rock salt phases, effectively improving the cycle performance of the lithium-rich manganese-based cathode material.

[0051] Therefore, this lithium-rich manganese-based preparation method addresses the defect of poor cycle performance of existing lithium-rich manganese-based materials. It can significantly improve the cycle stability of the material without damaging the material's rate performance, and this improvement trend becomes more obvious with the increase of the addition amount of M-MOFs within a certain range.

[0052] In one embodiment, a method for preparing a lithium-rich manganese-based positive electrode material comprises the following steps:

[0053] Preparation of Solution A: Dissolve lithium salt, nickel salt, cobalt salt, and manganese salt in a first mixed solvent according to the molar ratio of the molecular formula, and stir to obtain Solution A, wherein the first mixed solvent is a mixture of deionized water and anhydrous ethanol;

[0054] Preparation of Solution B: Dissolve anhydrous oxalic acid in a second mixed solvent and stir to obtain Solution B, wherein the second mixed solvent is a mixture of deionized water and anhydrous ethanol;

[0055] The amount of anhydrous oxalic acid added is sufficient to ensure that all the metal salts react.

[0056] Preparation of Solution C: TMA-M MOFs were added to Solution B according to the molar ratio of the molecular formula, and ultrasonic dispersion was performed to obtain Solution C, where TMA is dimethylimidazole, M includes at least one metal element, and MOFs is a metal-organic framework.

[0057] Preparation of the final product: Solution A was added dropwise to solution C under stirring, and the lithium-rich manganese-based positive electrode material was obtained after evaporation, sintering, and cooling to room temperature.

[0058] In one embodiment, M includes at least one transition metal element, or M includes any one of chromium, nickel, iron, cobalt, copper, zinc, silver, lanthanum, manganese, palladium, tin, magnesium, titanium and platinum.

[0059] This method for preparing a lithium-rich manganese-based cathode material eliminates the ball-milling process for mixing the lithium source and the M salt precursor by regulating the ratio of the TMA-M MOFs and applying an integrated Li-M element sintering process. It also enables gradient doping of the M element and modification of the hollow structure during the preparation process. The hollow structure of the resulting lithium-rich manganese-based cathode material releases stress accumulation during charge-discharge cycles, and the M element inhibits the migration of transition metal ions, significantly improving the material's discharge capacity and cycle stability. The fully exposed {010} crystal planes of the prepared lithium-rich manganese-based cathode material shorten the Li ion diffusion path of the material system, ensuring improved rate performance. This method for preparing a lithium-rich manganese-based cathode material requires low-cost raw materials, has stable process parameters, and produces no wastewater, exhaust gas, or toxic products, making it suitable for large-scale promotion and application.

[0060] The present application does not limit the lithium salt, and conventional lithium salts in the art can be used. In one embodiment of the present application, at least one of lithium acetate, lithium carbonate, lithium nitrate, and lithium sulfate can be used as the lithium salt.

[0061] The present application does not limit the nickel salt, and any conventional nickel salt in the art can be used. In one embodiment of the present application, at least one of nickel acetate, nickel carbonate, nickel nitrate, and nickel sulfate can be used as the nickel salt.

[0062] The present application does not limit the cobalt salt, and conventional cobalt salts in the art can be used. In one embodiment of the present application, at least one of cobalt acetate, cobalt carbonate, cobalt nitrate, and cobalt sulfate can be used as the cobalt salt.

[0063] The present application does not limit the manganese salt, and conventional manganese salts in the art can be used. In one embodiment of the present application, at least one of manganese acetate, manganese carbonate, manganese nitrate, and manganese sulfate can be used as the manganese salt.

[0064] In one embodiment, preferably, the volume ratio of deionized water to anhydrous ethanol in the first mixed solvent is 1:12;

[0065] Preferably, the volume ratio of deionized water to anhydrous ethanol in the second mixed solvent is 4:6.

[0066] Preferably, the stirring during the preparation of solution A is magnetic stirring, under the following conditions: magnetic stirring at a speed of 500 rpm to 1200 rpm for 10 min to 30 min. In other embodiments, other stirring methods may also be used.

[0067] Preferably, the stirring in the preparation of solution B is magnetic stirring, and the conditions are: magnetic stirring at a rotation speed of 500 rpm-1200 rpm for 10 min-40 min; in other embodiments, other stirring methods can also be used.

[0068] Preferably, the ultrasonic dispersion conditions during the preparation of solution C are: ultrasonic dispersion for 10 min-20 min;

[0069] Preferably, the stirring during the preparation of the final product is magnetic stirring, and the conditions are: magnetic stirring at a speed of 500 rpm-1200 rpm for 4 h-12 h;

[0070] Preferably, the evaporation conditions are: evaporation in an oven at 60°C-80°C for 48h-72h;

[0071] Preferably, the sintering conditions are: sintering at 300° C.-600° C. in an air atmosphere for 1 h-10 h, and then sintering at 700° C.-1000° C. in an air atmosphere for 4 h-24 h.

[0072] Low-temperature sintering first is beneficial to the uniform migration of elements in the reaction and the complete removal of water molecules, preparing for the later high-temperature synthesis.

[0073] Preferably, the cooling condition is: a cooling rate of 1K-20K / min.

[0074] It is conceivable that the above conditions may be changed as needed and are not limited to the above conditions.

[0075] In one embodiment, before the step of preparing solution C, the preparation of TMA-MMOFs is also included. The preparation of TMA-MMOFs includes:

[0076] M salt and TMA were dissolved in deionized water to form solution D and solution E, respectively;

[0077] Solution D was added dropwise into solution E, and TMA-M MOFs were prepared after stirring, washing, and drying.

[0078] In one embodiment, taking the preparation process of TMA-Cr MOFs as an example, 10mmol Cr(NO3)3·9H2O (4.001g) and 3mmol TMA (0.630g) were dissolved in 20mL-250mL deionized water, respectively, and magnetically stirred for 10min-40min until the reactants were completely dissolved to form solutions D and E, respectively. Solution D was slowly added dropwise to solution E, accompanied by magnetic stirring at 500rpm-1200rpm for 6h-48h. The product was collected, washed with deionized water 1-5 times, and then vacuum dried at 80℃-130℃ for 24h-72h before use. In other embodiments, the preparation process of other TMA-M (M is at least one metal element) MOFs is the same as the above process and will not be repeated here.

[0079] The present application also provides an electrode sheet, which is prepared using the lithium-rich manganese-based positive electrode material provided in any embodiment of the present application. Thus, the electrode sheet has excellent discharge specific capacity and cycle stability, so that a battery using the electrode sheet has a long cycle life and excellent discharge specific capacity.

[0080] The present application also provides a lithium-ion battery prepared using the electrode sheet of any of the above embodiments. Thus, the lithium-ion battery has a long cycle life and a relatively good discharge specific capacity.

[0081] The lithium-rich manganese-based positive electrode material prepared in Example 1 is as follows:

[0082] Li 1.2 (Ni 0.13 Co 0.13 Mn 0.54 ) 0.99 Cr 0.01 O2, lithium-rich manganese-based positive electrode material Li prepared in Example 2 1.2 (Ni 0.13 Co 0.13 Mn 0.54 ) 0.98 Cr 0.02 O2, lithium-rich manganese-based positive electrode material Li prepared in Example 3 1.2 (Ni 0.13 Co 0.13 Mn 0.54 ) 0.96 Cr 0.04 O2, lithium-rich manganese-based positive electrode material Li prepared in Example 4 1.2 (Ni 0.13 Co 0.13 Mn 0.54 ) 0.92 Cr 0.08 O2 and the lithium-rich manganese-based positive electrode material Li prepared in the comparative example 1.2 Ni0.13 Co 0.13 Mn 0.54 O2 was used for structural information comparison, morphology characterization and corresponding electrochemical performance testing to further illustrate this application.

[0083] Example 1

[0084] This embodiment provides a lithium-rich manganese-based positive electrode material, the chemical formula of which is

[0085] Li 1.2 (Ni 0.13 Co 0.13 Mn 0.54 ) 0.99 Cr 0.01 O2.

[0086] The lithium-rich manganese-based positive electrode material Li 1.2 (Ni 0.13 Co 0.13 Mn 0.54 ) 0.99 Cr 0.01 The method for preparing O2 comprises:

[0087] According to Li 1.2 (Ni 0.13 Co 0.13 Mn 0.54 ) 0.99 Cr 0.01 The molar number of metal sources other than Cr in the O2 chemical formula was calculated by weighing the corresponding acetates (CH3COOLi·2H2O=1.608g, Ni(CH3COO)2·4H2O=0.412g, Co(CH3COO)2·4H2O=0.412g, and Mn(CH3COO)2·4H2O=1.620g). These were dissolved in 260mL of a mixture of deionized water and anhydrous ethanol (volume ratio: water:ethanol=1:12) and magnetically stirred at 800rpm for 20min to form Solution A. 1.63g of anhydrous oxalic acid (H2C2O4) was dissolved in 100mL of a mixture of deionized water and anhydrous ethanol (volume ratio: water:ethanol=4:6) and magnetically stirred at 800rpm for 20min to form Solution B. The corresponding molar amount of TMA-Cr MOFs was added to Solution B and ultrasonically dispersed for 20min to form Solution C. Solution A was immediately added dropwise to solution E while magnetically stirring at 1200 rpm for 6 hours. After magnetic stirring, the solvent was evaporated in an oven at 80°C for 72 hours. The resulting powder was sintered at 500°C for 5 hours and then at 820°C for 20 hours in an air atmosphere. After cooling in an air atmosphere, a micron-shaped hollow rod of lithium-rich manganese-based positive electrode material Li was obtained. 1.2 (Ni 0.13 Co 0.13Mn 0.54 ) 0.99 Cr 0.01 O2.

[0088] Example 2

[0089] This embodiment provides a lithium-rich manganese-based positive electrode material, the chemical formula of which is

[0090] Li 1.2 (Ni 0.13 Co 0.13 Mn 0.54 ) 0.98 Cr 0.02 O2.

[0091] The specific preparation method was carried out with reference to Example 1. In this example, only the addition amounts of each metal salt and TMA-Cr MOFs were adjusted according to the molar amounts of the molecular formula (CH3COOLi·2H2O=1.608g, Ni(CH3COO)2·4H2O=0.408g, Co(CH3COO)2·4H2O=0.408g, Mn(CH3COO)2·4H2O=1.603g).

[0092] Example 3

[0093] This embodiment provides a lithium-rich manganese-based positive electrode material, the chemical formula of which is

[0094] Li 1.2 (Ni 0.13 Co 0.13 Mn 0.54 ) 0.96 Cr 0.04 O2.

[0095] The specific preparation method was carried out with reference to Example 1. In this example, only the addition amounts of each metal salt and TMA-Cr MOFs were adjusted according to the molar weight of the molecular formula (CH3COOLi·2H2O=1.608g, Ni(CH3COO)2·4H2O=0.399g, Co(CH3COO)2·4H2O=0.399g, Mn(CH3COO)2·4H2O=1.570g).

[0096] Example 4

[0097] This embodiment provides a lithium-rich manganese-based positive electrode material, the chemical formula of which is

[0098] Li 1.2 (Ni 0.13 Co 0.13 Mn 0.54 ) 0.92 Cr 0.08 O2.

[0099] The specific preparation method was carried out with reference to Example 1. In this example, only the addition amounts of each metal salt and TMA-Cr MOFs were adjusted according to the molar weight of the molecular formula (CH3COOLi·2H2O=1.608g, Ni(CH3COO)2·4H2O=0.383g, Co(CH3COO)2·4H2O=0.383g, Mn(CH3COO)2·4H2O=1.505g).

[0100] Comparative Example

[0101] This embodiment provides a lithium-rich manganese-based positive electrode material, the chemical formula of which is Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0102] The specific preparation method was similar to that of Example 1, using a coprecipitation-sintering process. The addition of TMA-Cr MOFs was omitted. For detailed preparation information, refer to the synthesis process in Example 1. The amounts of each metal salt were adjusted according to the molar weight of the molecular formula: (CH3COOLi·2H2O=1.608g, Ni(CH3COO)2·4H2O=0.416g, Co(CH3COO)2·4H2O=0.416g, Mn(CH3COO)2·4H2O=1.636g).

[0103] Comparison of structural information between Examples 1-4 and Comparative Examples

[0104] The lithium-rich manganese-based positive electrode materials prepared in the above examples 1, 2, 3, 4, and the comparative example were subjected to structural characterization analysis by an X-ray diffractometer (D8-discover, manufactured by Bruker, Germany), and the following were obtained: Figure 1 The results shown. Figure 1 It can be seen that all the diffraction peaks are very sharp, indicating that all five materials have good crystallinity, and the presence of Li2MnO3 with a c / 2m space group is observed in each sample. All synthesized examples are free of impurity peaks, and each diffraction peak corresponds one-to-one with the diffraction peaks of standard lithium-rich manganese-based materials.

[0105] Morphology characterization of TMA-Cr MOFs nucleating agent used in Examples 1-4

[0106] The TMA-Cr MOFs in the experimental steps of Examples 1-4 were characterized by scanning electron microscopy (ZEISS SUPRA 55) to obtain SEM images corresponding to a magnification of 30,000 times, as shown in FIG. Figure 2The figure clearly shows the rod-like aggregate morphology of TMA-Cr MOFs, with an individual diameter of approximately 50 nm. The size and aspect ratio are stable.

[0107] Micromorphology characterization of Example 4

[0108] The lithium-rich manganese-based cathode material prepared in Example 4 was characterized by scanning electron microscopy (ZEISS SUPRA 55) to obtain a SEM image at a magnification of 10,000 times, as shown in FIG. Figure 3 Through observation, it was found that the synthesized Example 4 showed micron rod morphology characteristics, a regular rectangular structure, and the formation of the internal hollow structure could be clearly observed. The size of the single particle was 2 microns * 8 microns.

[0109] Atomic-level morphology characterization of Example 4

[0110] The microstructure of the lithium-rich manganese-based cathode material prepared in Example 4 was observed by field emission transmission electron microscopy (JEOL-3200FS). Figure 4 As shown. Figure 4 It can be clearly seen from the high-resolution image that Example 4 exhibits a typical layered structure, which corresponds to its (003) crystal plane.

[0111] Comparison of electrochemical performance between Examples 1-4 and Comparative Example

[0112] The five lithium-rich manganese-based positive electrode materials prepared in Examples 1-4 and Comparative Examples were assembled into batteries for electrochemical performance testing and characterization. Here, Example 1 is used as an example to introduce the specific assembly process. Examples 2-4 and Comparative Examples are the same. The specific assembly steps are as follows:

[0113] 1. Preparation of positive electrode sheet

[0114] The lithium-rich manganese-based positive electrode material Li obtained in Example 1 1.2 (Ni 0.13 Co 0.13 Mn 0.54 ) 0.99 Cr 0.01 O2, conductive carbon black Super-P, and binder PVDF were thoroughly mixed in a mortar at a mass ratio of 8:1:1 and transferred to a 5mL beaker. An appropriate amount of NMP solution was then added for dispersion. The beaker was stirred on a magnetic stirrer for 4 hours, then evenly coated on aluminum foil. The mixture was then dried in an 80°C forced air oven. After drying for two hours, it was cut into 10mm diameter discs. The cut positive electrode sheets were then transferred to a 110°C vacuum oven and dried for 24 hours before use.

[0115] 2. Preparation of battery negative electrode

[0116] The negative electrode of the battery is a commercial lithium sheet with a diameter of 14mm purchased from AVIC Lithium.

[0117] 3. Button battery assembly

[0118] CR2032 button cells were assembled in an Ar-filled glove box. The electrolyte consisted of 1 mol / L LiPF6 dissolved in a 1:1 volume ratio of EC (ethylene carbonate) and DMC (dimethyl carbonate). Celgard 2400 polypropylene membrane was used as the separator. The assembly order, from top to bottom, was: positive electrode casing, positive electrode sheet, separator, negative electrode, steel sheet, spring sheet, and negative electrode casing. After assembly, the cells were allowed to rest for 12 hours before use.

[0119] 4. Battery performance test

[0120] The electrochemical test of the battery adopts the Xinwei electrochemical test system. Here, the button battery is placed on the Xinwei electrochemical test channel. The measured voltage range is 2.0V-4.8V, and the battery cycle stability is compared and tested.

[0121] Comparison of Cyclic Stability between Examples 1-4 and Comparative Example

[0122] The charge-discharge cycle test of Examples 1-4 and the comparative example was carried out at a charge-discharge rate of 1C (1C = 250 mA / g), and the number of cycles was 500. The results are as follows: Figure 5 As shown. The test results show that the capacity of the comparative example experienced a more serious decline during the cycle process, with the cycle capacity dropping from the initial 250 mAh / g to 100 mAh / g after 500 cycles, and the capacity retention rate was 40%. With the addition of TMA-Cr MOF, the discharge capacity and middle finger voltage of Examples 1-4 during the cycle process showed a trend of gradual improvement. The discharge specific capacity of Example 4 during the cycle process increased from the initial 212 mAh / g to 163 mAh / g after 500 cycles, with a retention rate of up to 76.8%. From the above comparison, it can be seen that the addition of TMA-Cr MOF is beneficial to improving the cycle stability of the examples.

[0123] The above examples are used to illustrate the present invention, which are only used to help understand the present invention and are not intended to limit the present invention. Those skilled in the art can make several simple deductions, modifications or substitutions based on the concept of the present invention.

Claims

1. Preparation method of lithium-rich manganese-based cathode material, the lithium-rich manganese-based cathode material is in the form of micron hollow rod structure, and the molecular formula of the lithium-rich manganese-based cathode material is Li 1.2 (Ni 0.13 Co 0.13 Mn 0.54 ) 1-x M x O2, where the value of x is 0 < x ≤ 0.08, and M includes at least one metal element, characterized in that, The preparation method of the lithium-rich manganese-based positive electrode material comprises: Solution A is prepared by dissolving a lithium salt, a nickel salt, a cobalt salt, and a manganese salt in a first mixed solvent according to a molar ratio, and stirring to obtain solution A, wherein the first mixed solvent is a mixture of deionized water and anhydrous ethanol; Preparation of Solution B: Dissolve anhydrous oxalic acid in a second mixed solvent and stir to obtain Solution B, wherein the second mixed solvent is a mixture of deionized water and anhydrous ethanol; Preparation of solution C: TMA-M MOFs was added to solution B according to a molar ratio, and solution C was obtained after ultrasonic dispersion, wherein TMA was dimethylimidazole and MOFs was a metal organic framework; The final product is prepared by adding the solution A dropwise into the solution C while stirring, evaporating, sintering, and cooling to room temperature to obtain the lithium-rich manganese-based positive electrode material; the sintering conditions are: sintering in an air atmosphere at 300°C-600°C for 1h-10h, and then sintering in an air atmosphere at 700°C-1000°C for 4h-24h.

2. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 1, wherein: The lithium salt is at least one of lithium acetate, lithium carbonate, lithium nitrate and lithium sulfate; and / or the nickel salt is at least one of nickel acetate, nickel carbonate, nickel nitrate and nickel sulfate; and / or the cobalt salt is at least one of cobalt acetate, cobalt carbonate, cobalt nitrate and cobalt sulfate; and / or the manganese salt is at least one of manganese acetate, manganese carbonate, manganese nitrate and manganese sulfate.

3. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The volume ratio of deionized water to anhydrous ethanol in the first mixed solvent is 1:12; The volume ratio of deionized water to anhydrous ethanol in the second mixed solvent is 4:6; The stirring in the preparation of the solution A is magnetic stirring, and the conditions are: magnetic stirring at a speed of 500 rpm-1200 rpm for 10 min-30 min; The stirring in the preparation of the solution B is magnetic stirring, and the conditions are: magnetic stirring at a speed of 500 rpm-1200 rpm for 10 min-40 min; The ultrasonic dispersion conditions during the preparation of solution C are as follows: ultrasonic dispersion for 10 min-20 min; The stirring during the preparation of the final product is magnetic stirring, and the conditions are: magnetic stirring at a speed of 500 rpm-1200 rpm for 4 h-12 h; The evaporation conditions are: evaporation in an oven at 60°C-80°C for 48h-72h; The cooling condition is: a cooling rate of 1K-20K / min.

4. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 1, wherein: Before the step of preparing the solution C, the preparation of TMA-M MOFs is also included, and the preparation of the TMA-M MOFs includes: M salt and TMA were dissolved in deionized water to form solution D and solution E, respectively; The solution D was added dropwise into the solution E, and the mixture was stirred, washed, and dried to obtain TMA-MMOFs.

5. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 1, wherein: The M includes any one of chromium, nickel, iron, cobalt, copper, zinc, silver, lanthanum, manganese, palladium, tin, magnesium, titanium and platinum, or the M includes at least one transition metal element.

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