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

Abstract

This invention discloses a lithium-rich manganese-based cathode material, its preparation method, and its application, belonging to the field of new energy materials and advanced battery technology. The lithium-rich manganese-based cathode material provided by this invention is assembled from active particles and has a one-dimensional linear structure; the active particles have a double-core-shell structure, wherein the core is a layered lithium-rich manganese material, and the middle layer is a spinel-type Li4Mn5O. 12 The outer shell is a carbon layer. In the lithium-rich manganese-based cathode material provided by this invention, the double-layer core-shell structure can effectively suppress the irreversible transformation of the core from a layered to a disordered rock salt phase during cycling. Simultaneously, by utilizing the axial electron conduction advantage of the one-dimensional linear structure and the interfacial stability of the functionalized intermediate and shell layers, the specific capacity, rate performance, and long cycle life of the lithium-rich manganese-based cathode material are synergistically improved, providing an innovative solution for the development of high-energy-density lithium-ion batteries. This invention also provides a method for preparing the above-mentioned lithium-rich manganese-based cathode material and its applications.

Description

Technical Field

[0001] This invention relates to the fields of new energy materials and advanced battery technology, and in particular to a lithium-rich manganese-based cathode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of new energy vehicles and large-scale energy storage technologies, the energy density, cycle life, and rate performance of lithium-ion battery cathode materials have become key factors restricting their application. Lithium-rich manganese-based cathode materials (Li-rich Mn-based layered oxides) are considered key materials for next-generation high-energy-density batteries due to their high specific capacity (>250 mAh / g) and low cost. However, traditional lithium-rich manganese-based cathode materials generally suffer from irreversible release of lattice oxygen and irreversible structural phase transitions during cycling, leading to problems such as voltage decay, intensified side reactions at the electrode and electrolyte interface, and insufficient ionic / electron conductivity. These problems severely limit the practical application of lithium-rich manganese-based cathode materials.

[0003] In traditional techniques, researchers typically employ surface coating (such as Al2O3, Li3PO4, and TiO2) and bulk doping (such as Al...). 3+ Ce 3+ and Nb 5+ The performance of lithium-rich manganese-based cathode materials can be improved by single modification methods such as structural nano-sizing, but the above modification methods have the following limitations: (1) The simple coating layer has weak bonding force with the matrix (core) and is easy to fall off during charging and discharging; (2) Homogeneous doping is difficult to achieve both bulk structure stability and surface activity regulation at the same time; (3) Conventional nanoparticles are easy to agglomerate and the lithium ion diffusion path is disordered.

[0004] Besides the basic modification methods mentioned above, in recent years, gradient heterostructure design (such as core-shell structures and compositional gradient distributions) has been considered to improve the stability of lithium-rich manganese-based cathode materials by alleviating lattice mismatch stress, inhibiting transition metal dissolution, and regulating oxygen activity. However, existing preparation methods (such as stepwise precipitation and high-temperature solid-state diffusion) generally face problems such as complex processes and imprecise multi-scale structural control, making it difficult to achieve synergistic optimization of continuous compositional gradients and heterostructure interfaces from the core to the surface. Therefore, the modification effect is not significant.

[0005] In summary, it is particularly important to improve the lattice structure stability and interface stability of lithium-rich manganese-based cathode materials, thereby enhancing their electrochemical performance in terms of capacity, rate capability, and cycle life. Summary of the Invention

[0006] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a lithium-rich manganese-based cathode material with excellent structural and interfacial stability, thereby exhibiting high capacity, as well as excellent rate and cycle performance.

[0007] The present invention also provides a method for preparing the above-mentioned lithium-rich manganese-based cathode material.

[0008] This invention also provides applications of the above-mentioned lithium-rich manganese-based cathode material.

[0009] According to an embodiment of the first aspect of the present invention, a lithium-rich manganese-based cathode material is provided, the lithium-rich manganese-based cathode material being assembled from active particles and having a one-dimensional linear structure;

[0010] The active particles have a double core-shell structure, wherein the core is a layered lithium-rich manganese material, and the middle layer includes spinel-type Li4Mn5O. 12 The outer shell is a carbon layer.

[0011] The lithium-rich manganese-based cathode material according to embodiments of the present invention has at least the following beneficial effects:

[0012] In the lithium-rich manganese-based cathode material provided by this invention, the core layer enhances the specific capacity and energy density, while the intermediate layer, as a three-dimensional fast diffusion channel for lithium ions, significantly improves the ion diffusion coefficient, alleviates interfacial stress, inhibits phase transition and irreversible oxygen evolution, and also mitigates electrolyte erosion of the core to a certain extent. The outer shell layer enhances electronic conductivity and isolates the electrolyte from erosion of the bulk phase of the lithium-rich manganese-based cathode material. The one-dimensional linear structure is assembled from active particles, and the axial arrangement further optimizes the lithium ion diffusion path and bulk phase structural stability.

[0013] The lithium-rich manganese-based cathode material provided by this invention features a double-layer core-shell structure, which effectively forms a gradient heterostructure. This structure can effectively suppress the irreversible transformation of the core layered structure into a disordered rock salt phase during cycling, suppress lattice oxygen release during charge and discharge, and improve anion oxygen activity. Simultaneously, it utilizes the axial electron conduction advantage of the one-dimensional linear structure and the interfacial stability of the surface functionalized modification (double-shell structure). The synergistic effect between the above structure and material jointly suppresses problems such as voltage decay, increased interfacial side reactions, and insufficient ion / electron conductivity during cycling. This improves the specific capacity, rate performance, and long cycle life of the lithium-rich manganese-based cathode material, providing an innovative solution for the development of high-energy-density lithium-ion batteries.

[0014] In summary, through the synergistic effect between structure and material, the lithium-rich manganese-based cathode material provided by this invention has a lithium-ion diffusion coefficient that is 1 to 2 orders of magnitude higher than that of traditional lithium-rich manganese materials; the capacity retention rate can be ≥90% after 400 cycles; and the specific capacity can be ≥200mAh / g at 1C rate.

[0015] According to some embodiments of the present invention, the thickness of the intermediate layer is 2 to 20 nm. For example, it can be about 5 nm, 8 nm, 10 nm, 12 nm, or about 15 nm.

[0016] According to some embodiments of the present invention, the thickness of the outer shell layer is 2 to 5 nm. For example, it can be about 3 nm or about 4 nm.

[0017] According to some embodiments of the present invention, the carbon layer is made of amorphous carbon.

[0018] According to some embodiments of the present invention, the particle size of the active particles is 80-120 nm. For example, it can be about 90 nm, 100 nm, or about 110 nm.

[0019] According to some embodiments of the present invention, the diameter of the one-dimensional linear structure is 450-550 nm. For example, it can be about 480 nm, 500 nm, or about 520 nm.

[0020] According to some embodiments of the present invention, the length of the one-dimensional linear structure is 4.5 to 5.5 μm. For example, it can be about 4.8 μm, 5.0 μm, or about 5.2 μm.

[0021] According to some embodiments of the present invention, the aspect ratio of the one-dimensional linear structure is 9 to 11. For example, it can be about 10.

[0022] According to some embodiments of the present invention, the chemical formula of the core is Li. 1.2 M 0.8 O2; and M includes Mn. Therefore, the lattice matching between the core and the intermediate layer is optimal, resulting in excellent electrochemical performance of the lithium-rich manganese-based cathode material.

[0023] According to some embodiments of the present invention, the Li 1.2 M 0.8 In O2, M also includes at least one of Ni and Co. Mn accounts for 50-60% of the molar percentage of M; specifically, it can be about 52%, 54%, 56%, or about 58%. Ni accounts for 10-15% of the molar percentage of M; specifically, it can be about 11%, 12%, 13%, or about 14%. The balance is Co.

[0024] According to some embodiments of the present invention, the chemical formula of the core is Li. 1.2Mn 0.54 Ni 0.13 Co 0.13 O2.

[0025] According to some embodiments of the present invention, the general chemical formula of the core and intermediate layer is as follows: x Li4Mn5O 12 ·( 1-x Li 1.2 M 0.8 The value of x for O2 ranges from 1% to 10%. x can be determined based on the thickness of the intermediate layer and the particle size of the resulting active particles in actual production. For example, when the thickness of the intermediate layer is approximately 5 nm, the value of x is approximately 3%.

[0026] According to an embodiment of a second aspect of the present invention, a method for preparing the lithium-rich manganese-based cathode material described in the first aspect of the present invention is provided, the method comprising the following steps:

[0027] S1. The transition metal source of the layered lithium-rich manganese material is mixed and dispersed with nitrotriacetic acid (NTA) and then subjected to a solvothermal reaction to obtain the first precursor;

[0028] S2. The first precursor and the lithium source are mixed according to the molar ratio of lithium:metal = 1.05~1.20:0.8 to obtain the second precursor;

[0029] S3. Calcining the second precursor in an oxygen-containing atmosphere;

[0030] The calcination includes a first stage of calcination and a second stage of calcination performed sequentially.

[0031] The calcination temperature of the first stage is 300~500℃;

[0032] The calcination temperature of the second stage is 800~900℃.

[0033] The partial mechanism of the preparation method is as follows:

[0034] In step S3, the first calcination mainly achieves in-situ carbonization of the hyponitrotriacetic acid to form a corresponding carbon layer; at the same time, lithium ions in the lithium source are initially inserted; the lower calcination temperature suppresses excessive diffusion of lithium ions and ensures the uniformity of the core composition.

[0035] The second stage of calcination, at a high temperature, significantly increases the lithium-ion diffusion rate. Combined with the lithium:metal ratio in step S2, it can induce the formation of the spinel phase (lithium-poor phase) of the intermediate layer on the surface of the core (lithium-rich phase), thereby creating a lithium concentration gradient.

[0036] Since the preparation method employs all the technical solutions of the lithium-rich manganese-based cathode materials described in the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments. Specifically, the obtained lithium-rich manganese-based cathode material exhibits excellent cycle performance, rate performance, and energy density. Furthermore, the preparation method also has the following advantages:

[0037] In step S1, the self-assembly characteristics of NTA ligands and free metal ions (from the transition metal source) are utilized to ensure the uniform distribution of transition metal ions on NTA to achieve uniform in-situ carbonization behavior, ultimately obtaining a carbon layer with uniform thickness.

[0038] In step S2, by adjusting the lithium:metal ratio and combining it with the calcination mechanism in step S3, the thickness of the intermediate layer can be effectively controlled. Specifically, the intermediate layer is a lithium-poor, manganese-rich phase (Li:Mn ratio less than 1). Within the range provided by this invention, the stoichiometry of the added lithium source gradually decreases. During the calcination process in step S3, as lithium diffuses from the surface to the bulk phase, it is easier to form a lithium-poor spinel-type Li4Mn5O phase in the intermediate layer. 12 Furthermore, the smaller the proportion of lithium source added, the thicker the intermediate layer. If it is below the above range, it is difficult to form a lithium-rich manganese material core; if it is above the above range, it is difficult to form an intermediate layer.

[0039] In step S3, one-dimensional morphology control and spinel phase formation are simultaneously achieved in a single system, avoiding interface defects of traditional step-by-step processes. A two-stage calcination strategy is adopted to precisely control the structural phase transformation (intermediate layer) and the carbon layer thickness of the outer shell layer, ensuring tight bonding at the heterogeneous interface. This is more conducive to improving the performance of the lithium-rich manganese-based cathode material.

[0040] The preparation method achieves microstructure design and multifunctional modification by controlling the nucleation-growth kinetics of the first precursor at the molecular scale. It simultaneously realizes the self-assembly and directional growth of one-dimensional nanostructures and the formation of layered lithium-rich manganese material cores (Li) in a single reaction system. 1.2 M 0.8 O2) structure, spinel-type Li4Mn5O 12 The construction of the intermediate layer and the outer shell amorphous carbon layer. The preparation method is simple and easy to implement.

[0041] According to some embodiments of the present invention, in step S1, the transition metal source includes at least one of transition metal chloride, nitrate, sulfate and acetate.

[0042] According to some embodiments of the present invention, in step S1, the transition metal source is a transition metal chloride salt.

[0043] According to some embodiments of the present invention, in step S1, the transition metal source includes a manganese source.

[0044] According to some embodiments of the present invention, the manganese source includes at least one of manganese chloride, manganese nitrate, manganese sulfate, manganese acetate, or their hydrates.

[0045] According to some embodiments of the present invention, in step S1, the transition metal source further includes at least one of a nickel source and a cobalt source.

[0046] According to some embodiments of the present invention, the nickel source includes at least one of nickel chloride, nickel nitrate, nickel sulfate, nickel acetate, or their hydrates. For example, it may specifically be nickel chloride hexahydrate.

[0047] According to some embodiments of the present invention, the cobalt source includes at least one of cobalt chloride, cobalt sulfate, cobalt acetate, cobalt nitrate, or their hydrates. For example, it may specifically be cobalt chloride hexahydrate.

[0048] In step S1, when there are ≥2 types of transition metal sources, each transition metal source undergoes a solvothermal reaction with the hypozinotriacetic acid alone. This yields ≥2 types of first precursors (referred to as Mn-NTA, Co-NTA, and Ni-NTA depending on the type of transition metal source). Here, the type of transition metal source is determined by the type of transition metal it contains. For example, nickel nitrate and nickel sulfate are two salts, but they only contain nickel, therefore they are counted as one transition metal source. The types of transition metal sources in other positions of this invention are calculated based on the specific reagent type.

[0049] When the number of types of the first precursor obtained in step S1 is greater than one, the following mechanism also applies:

[0050] Since the first precursor contains NTA, and the NTA molecule has unsaturated carboxylic acid, the subsequent addition of lithium salt forms bonds with different first precursors. The combination and molecular forces between different first precursors aggregate the different first precursors together. In the calcination of step S3, the metals in the different first precursors diffuse into each other and further fuse into continuous nanoparticles. The active particles are all on a one-dimensional linear structure.

[0051] Furthermore, due to the different proportions of the same metal element in different first precursors, the metal diffuses from high concentration to low concentration during the calcination process in step S3; that is, Ni diffuses from Ni-NTA to Mn-NTA / Co-NTA (where the Ni concentration is low), and similarly, Co diffuses from Co-NTA to Mn-NTA / Ni-NTA (where the Co concentration is low). The synthesized typical lithium-rich manganese Li 1.2 Mn 0.54 Ni 0.13 Co 0.13The high stoichiometry of manganese in O2 further facilitates the diffusion of more Ni / Co from the surface into the bulk phase during the two-step calcination process, forming a core. This makes it easier for the intermediate layer to form a lattice-matched, lithium-poor, manganese-rich Li4Mn5O phase. 12 .

[0052] According to some embodiments of the present invention, when the transition metal source is a manganese source, the molar ratio of the manganese source to the hyponitrotriacetic acid is 1.8 to 2.2:1; specifically, it can be about 2:1; in the obtained first precursor, the mass percentage of Mn is 25 to 35%; specifically, it can be about 28%, 30%, or about 32%.

[0053] According to some embodiments of the present invention, when the transition metal source is a nickel source, the molar ratio of the nickel source to the hyponitrotriacetic acid is 1.8 to 2.2:1; specifically, it can be about 2:1; in the obtained first precursor, the mass percentage of Ni is 25 to 35%; specifically, it can be about 28%, 30%, or about 32%.

[0054] According to some embodiments of the present invention, when the transition metal source is a cobalt source, the molar ratio of the cobalt source to the hyponitrotriacetic acid is 1.8 to 2.2:1; specifically, it can be about 2:1; in the obtained first precursor, the mass percentage of Co is 15 to 25%; specifically, it can be about 18%, 20%, or about 22%.

[0055] According to some embodiments of the present invention, in step S1, the solvent used in the solvothermal method is a mixture of water and isopropanol. The volume ratio of water to isopropanol is 6-8:1; specifically, it can be about 7:1.

[0056] According to some embodiments of the present invention, in step S1, the mass-to-volume ratio of the hypozinotriacetic acid and the solvent is 3g:180~220mL. For example, it can be approximately 3g:200mL.

[0057] According to some embodiments of the present invention, in step S1, the temperature of the solvothermal reaction is 150–200°C. For example, it can be about 160°C, 170°C, 180°C, or about 190°C.

[0058] According to some embodiments of the present invention, in step S1, the duration of the solvothermal reaction is 12-24 hours. For example, it can be about 15 hours or about 20 hours. The duration of the solvothermal reaction affects the length of the one-dimensional linear structure of the first precursor; specifically, the longer the solvothermal reaction time, the longer the one-dimensional linear structure formed.

[0059] According to some embodiments of the present invention, step S1 further includes sequentially performing solid-liquid separation, washing, and drying after the solvothermal reaction.

[0060] To improve the safety of the experimental operation, the mixture obtained from the solvothermal reaction needs to be cooled before the solid-liquid separation.

[0061] The solid-liquid separation method includes vacuum filtration.

[0062] The drying temperature is 50~80℃; specifically, it can be about 60℃.

[0063] According to some embodiments of the present invention, in step S1, the first precursor has a one-dimensional linear structure.

[0064] According to some embodiments of the present invention, in step S2, the lithium source includes at least one of lithium carbonate, lithium nitrate, lithium chloride, lithium acetate, and lithium hydroxide.

[0065] According to some embodiments of the present invention, in step S2, the lithium source is lithium hydroxide.

[0066] According to some embodiments of the present invention, in step S2, the mixing includes wet mixing.

[0067] The wet mixing process includes obtaining a dispersion of the first precursor and a lithium salt solution, and then mixing and drying them. No solid-liquid separation is performed during the process, thus clarifying the lithium metal ratio, and the wet mixing significantly improves the dispersion uniformity between the lithium salt and the first precursor. Furthermore, the order of adding the dispersion and lithium salt solution is not strictly limited; in actual production, a suitable order can be chosen based on operational convenience, but the order of addition has no significant impact on the final result.

[0068] The dispersion of the first precursor and the solvent of the lithium salt solution are independently selected from at least one of ethanol and water.

[0069] In the dispersion of the first precursor, the solid-liquid ratio is 1g:15~50mL. For example, it can be approximately 1g:20mL, 1g:25mL, 1g:30mL, 1g:31mL, 1g:35mL, or approximately 1g:40mL.

[0070] The mass-to-volume ratio of solute to solvent in the lithium salt solution is 2.5~3.4g:200mL. For example, it can be approximately 3g:200mL, 2.8g:200mL, or 2.9g:200mL.

[0071] In the first precursor and lithium source, the molar ratio of lithium to metal is 1.05~1.2:0.8; for example, it can be about 1.1:0.8, 1.12:0.8, 1.14:0.8, 1.16:0.8, 1.18:0.8 or about 1.2:0.8.

[0072] The drying temperature is 60–90°C. For example, it can be approximately 70°C or approximately 80°C.

[0073] The drying time is 2 to 18 hours. For example, it can be 5 hours, 8 hours, 10 hours, 12 hours, or about 15 hours.

[0074] According to some embodiments of the present invention, in step S2, the mixing time is 2 to 5 hours. For example, it can be about 3 hours or about 4 hours.

[0075] According to some embodiments of the present invention, in step S3, the partial pressure of oxygen in the oxygen-containing atmosphere is 18-25%; for example, it can be about 20% or about 22%.

[0076] According to some embodiments of the present invention, in step S3, the calcination atmosphere is air. Air has a suitable oxygen partial pressure, which, combined with the two-stage calcination mechanism, ensures that the carbon layer is located in the outer shell layer, rather than being doped or existing in other locations.

[0077] According to some embodiments of the present invention, in step S3, the heating rate of the calcination is 2 to 5 °C / min. Within this range, phase separation or structural collapse caused by rapid heating is avoided, ensuring a tight bond between the core of the layered structure and the gradient interface of the spinel phase intermediate layer.

[0078] According to some embodiments of the present invention, in step S3, the duration of the first calcination is 5 to 10 hours; for example, it can be about 6 hours, 7 hours, 8 hours or about 9 hours.

[0079] According to some embodiments of the present invention, in step S3, the temperature of the first calcination stage is 400~500°C; for example, it can be about 420°C, 450°C or about 480°C.

[0080] According to some embodiments of the present invention, in step S3, the duration of the second calcination stage is 10 to 20 hours. For example, it can be approximately 12 hours, 14 hours, 16 hours, or approximately 18 hours.

[0081] According to some embodiments of the present invention, in step S3, the temperature of the second calcination stage is 850~900°C. For example, it can be approximately 880°C.

[0082] According to an embodiment of a third aspect of the present invention, a lithium-ion battery is provided, wherein the raw materials for preparing the lithium-ion battery include the lithium-rich manganese-based cathode material provided in the first aspect of the present invention.

[0083] Since the lithium-ion battery adopts all the technical solutions of the lithium-rich manganese-based cathode material of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments.

[0084] According to some embodiments of the present invention, the lithium-ion battery includes at least one of button cells, pouch cells, cylindrical cells, and prismatic cells.

[0085] According to some embodiments of the present invention, the negative electrode material of the lithium-ion battery includes at least one of lithium metal, carbon-based negative electrode, and silicon-based negative electrode. In actual production, other types of available negative electrode materials can also be used, and the present invention does not impose strict limitations.

[0086] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0087] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0088] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0089] Figure 1 The X-ray diffraction (XRD) patterns of the lithium-rich manganese-based cathode materials obtained in Examples 1, 2 and Comparative Example 1 of this invention are shown below.

[0090] Figure 2 The X-ray photoelectron spectroscopy (XPS) spectra of the lithium-rich manganese-based cathode materials obtained in Examples 1, 2, and Comparative Example 1 of this invention are shown below.

[0091] Figure 3 These are scanning electron microscope (SEM) images of the lithium-rich manganese-based cathode materials obtained in Examples 1, 2, and Comparative Example 1 of the present invention.

[0092] Figure 4 These are high-resolution transmission electron microscope (HRTEM) images of the lithium-rich manganese-based cathode materials obtained in Examples 1, 2, and Comparative Example 1 of this invention.

[0093] Figure 5 The rate performance diagrams are for the lithium-rich manganese-based cathode materials obtained in Examples 1, 2, and Comparative Example 1 of this invention.

[0094] Figure 6 The lithium-rich manganese-based cathode materials obtained in Examples 1, 2, and Comparative Example 1 of this invention were subjected to 1C (250 mA g) at 1C. -1 The long-cycle performance diagram under the given conditions.

[0095] Figure 7The graph shows the lithium-ion diffusion coefficient calculated from the GITT curves of the lithium-rich manganese-based cathode materials obtained in Examples 1, 2 and Comparative Example 1 of this invention under 0.1C conditions.

[0096] Figure 8 The first charge-discharge curves of the lithium-rich manganese-based cathode materials obtained in Example 1 and Comparative Example 2 of this invention are shown under 0.1C conditions.

[0097] Figure 9 The cycling performance of the lithium-rich manganese-based cathode materials obtained in Example 1 and Comparative Example 2 of this invention under 0.1C conditions is shown.

[0098] Figure 10 This is a transmission electron microscope (TEM) image of the lithium-rich manganese-based cathode material obtained in Example 1 of the present invention. Detailed Implementation

[0099] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0100] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0101] In the specific implementation, the water has a resistivity greater than or equal to that of deionized water; for example, it can be at least one of deionized water, ultrapure water, or (multiple) distilled water.

[0102] Example 1

[0103] This embodiment prepares a lithium-rich manganese-based cathode material with a double core-shell structure, wherein the core has the chemical formula Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 has a layered structure; the chemical formula of the middle layer is Li4Mn5O. 12 It is a spinel phase; the outer shell is an amorphous carbon layer.

[0104] The specific preparation method is as follows:

[0105] S1. Weigh 1.20g of manganese chloride and 0.90g of hypotriacetic acid, add 60mL of a water / isopropanol mixture with a volume ratio of 7:1, stir magnetically until a homogeneous solution is formed, transfer to a polytetrafluoroethylene reactor, heat to 180℃ and keep at that temperature for 24h, cool, filter, wash and dry at 60℃ to obtain one-dimensional white Mn-NTA, wherein the mass percentage of Mn is 30%;

[0106] Weigh 2.20 g of cobalt chloride hexahydrate and 0.90 g of nitric acid triacetic acid, add 60 mL of a water / isopropanol mixture with a volume ratio of 7:1, and stir magnetically until a homogeneous solution is formed. Transfer the solution to a polytetrafluoroethylene reactor, heat to 180 °C and keep at that temperature for 24 h. After cooling, filtering and washing, one-dimensional pink Co-NTA is obtained, in which the mass percentage of Co is 30%.

[0107] Weigh 2.20 g of nickel chloride hexahydrate and 0.90 g of triacetic acid, add 60 mL of a water / isopropanol mixture with a volume ratio of 7:1, and stir magnetically until a homogeneous solution is formed. Transfer the solution to a polytetrafluoroethylene reactor, heat to 180 °C and keep at that temperature for 24 h. After cooling, filtering and washing, one-dimensional blue Ni-NTA is obtained, in which the mass percentage of Ni is 20%.

[0108] Among them, Mn-NTA, Co-NTA and Ni-NTA are three primary precursors.

[0109] S2. A proportional description is given using the preparation of approximately 10 mmol of lithium-rich manganese-based cathode material as an example:

[0110] Weigh 1.10 g of Mn-NTA, 0.38 g of Ni-NTA, and 0.25 g of Co-NTA and add them to 50 mL of anhydrous ethanol. Stir and disperse to form a uniform and colorless dispersion of the metal complex. Weigh 0.30 g of anhydrous lithium hydroxide and add it to 20 mL of deionized water. Stir until the lithium hydroxide is completely dissolved to obtain a solution. Add the dispersion to the solution and stir for 3 h to form a uniform dispersion. Then transfer it to a drying oven at 90 °C and dry for 12 h to obtain a lithium-containing second precursor.

[0111] S3. The second precursor obtained in calcination step S2: calcination includes a first stage of calcination and a second stage of calcination performed sequentially.

[0112] The first stage of calcination: the temperature is raised to 450°C in air at a rate of 5°C / min and held for 6 hours to allow the NTA ligands to carbonize in situ and form an amorphous carbon layer (shell layer).

[0113] The second stage of calcination involves heating the air at a rate of 5°C / min to 900°C and holding it at that temperature for 12 hours to promote the formation of the intermediate layer.

[0114] The lithium-rich manganese-based cathode material obtained by natural cooling to room temperature is labeled SL-LMNCO-1.

[0115] Example 2

[0116] This embodiment prepares a lithium-rich manganese-based cathode material, which differs from Example 1 in that:

[0117] In step S2, the mass of anhydrous lithium hydroxide used is 0.28 g.

[0118] Correspondingly, the thickness of the resulting intermediate layer is different from that in Example 1.

[0119] The lithium-rich manganese-based cathode material is labeled SL-LMNCO-2.

[0120] Comparative Example 1

[0121] This comparative example prepared a lithium-rich manganese-based cathode material, which differs from Example 1 in that:

[0122] In step S2, the mass of lithium hydroxide used is 0.32 g;

[0123] Correspondingly, this excludes the intermediate layer.

[0124] The resulting lithium-rich manganese-based cathode material is labeled LMNCO.

[0125] Comparative Example 2

[0126] This comparative example prepared a lithium-rich manganese-based cathode material, which differs from Example 1 in that:

[0127] In step S3, the temperature of the second calcination stage is 700℃;

[0128] Correspondingly, the resulting lithium-rich manganese-based cathode material does not include an intermediate layer.

[0129] The resulting lithium-rich manganese-based cathode material is labeled LMNCO-1.

[0130] Application examples

[0131] This example demonstrates the fabrication of a lithium-ion battery, specifically:

[0132] Positive electrode sheet: Weigh 0.32g of lithium-rich manganese-based positive electrode material prepared in the examples or comparative examples, add 0.04g of conductive carbon black as a conductive agent, and 0.04g of PVDF (polyvinylidene fluoride, prepared by adding 5% NMP solution by mass) as a binder. After mixing evenly, coat it on aluminum foil, and vacuum dry it at 90°C for 12h. Cut it into round sheets with a diameter of 12mm.

[0133] Negative electrode: Lithium metal sheet.

[0134] Diaphragm: Celgard 2500 diaphragm.

[0135] Electrolyte: 1 mol / L LiPF6 / EC:DMC:EMC (volume ratio 1:1:1).

[0136] Assembly: In an argon-filled glove box, stack the components in the order of positive electrode, separator, and negative electrode, and immerse them in electrolyte; assemble them into a CR2016 button cell.

[0137] Test case

[0138] The first aspect of this example tested the XRD of the lithium-rich manganese-based cathode materials obtained in the examples and comparative examples. The results showed that Examples 1, 2, and Comparative Example 1 all exhibited typical layered α-NaFeO2 structures with space group R-3m. Simultaneously, a relatively obvious Li2MnO3 superlattice diffraction peak appeared between 20° and 25°, which is a characteristic peak of layered lithium-rich manganese materials with space group C2 / m. Samples SL-LMNCO-1 and SL-LMNCO-2 showed characteristic XRD diffraction peaks of a spinel phase (space group Fd-3m) at 36°~38° and 44°~46°, indicating the formation of a spinel-type Li4Mn5O3 intermediate layer. 12 XRD test results show that the product prepared in the embodiments of the present invention simultaneously possesses a spinel phase and a layered phase. The XRD test results of the embodiments and Comparative Example 1 are as follows: Figure 1 As shown.

[0139] The second aspect of this example tested the XPS spectra of the lithium-rich manganese-based cathode materials obtained in the examples and comparative examples. The results showed that the lithium-rich manganese-based cathode material obtained in Example 1 had obvious characteristic peaks of carbon, indicating that the lithium-rich manganese-based cathode material prepared by this invention contains carbon. Figure 2 As shown in the image.

[0140] The third aspect of this example obtained the morphology of the lithium-rich manganese-based cathode materials obtained in the examples and comparative examples using scanning electron microscopy (SEM). The results showed that the lithium-rich manganese-based cathode materials obtained in the examples and comparative examples maintained a well-defined one-dimensional linear structure. This demonstrates that the preparation method provided by this invention successfully synthesized a lithium-rich manganese-based cathode material with a one-dimensional linear structure formed by self-assembled nanoparticles. The SEM morphology of the lithium-rich manganese-based cathode materials obtained in the examples and comparative examples is shown below. Figure 3 As shown, (a) is a scanning electron microscope (SEM) image of the lithium-rich manganese-based cathode material obtained in Example 1, (b) is a scanning electron microscope (SEM) image of the lithium-rich manganese-based cathode material obtained in Example 2, and (c) is a scanning electron microscope (SEM) image of the lithium-rich manganese-based cathode material obtained in Comparative Example 1.

[0141] The fourth aspect of this example tested the microstructure of the lithium-rich manganese-based cathode materials obtained in the examples and comparative examples using high-resolution transmission electron microscopy (HRTEM). The results showed that the lithium-rich manganese-based cathode materials obtained in the examples and comparative examples were indeed one-dimensional linear structures assembled from active particles, with each active particle having a diameter of approximately 100 nm. Each active particle possessed a double-layer core-shell structure, with an outer shell of approximately 2 nm amorphous carbon layer, an intermediate layer of approximately 5 nm spinel phase in SL-LMNCO-1, and an intermediate layer of approximately 10 nm spinel phase in SL-LMNCO-2. The comparative example lacked an intermediate layer. The tests demonstrated that, using the preparation method provided by this invention, by adjusting the lithium metal ratio of the added lithium source and the first precursor, lithium-rich manganese-based cathode materials with a double-layer core-shell structure, a gradient heterostructure, and a one-dimensional linear structure can be successfully prepared. The high-resolution transmission electron microscopy results of examples and comparative example 1 are as follows: Figure 4 As shown, (a) is a transmission electron microscope (TEM) image of the lithium-rich manganese-based cathode material obtained in Example 1, (b) is a TEM image of the lithium-rich manganese-based cathode material obtained in Example 2, and (c) is a TEM image of the lithium-rich manganese-based cathode material obtained in Comparative Example 1; the TEM image of the lithium-rich manganese-based cathode material obtained in Example 1 is shown below. Figure 10 As shown.

[0142] The test results of the third and fourth aspects of the present invention also show that the one-dimensional linear structure of the lithium-rich manganese-based cathode material prepared by the present invention has a length of about 5 μm and a diameter of about 500 nm, that is, an aspect ratio of about 10.

[0143] The test results of the first to fourth aspects of the present invention also show that the results of comparative examples 1 to 2 are comparable, and all of them do not contain an intermediate layer.

[0144] Based on the above four test results, it can be seen that the lithium-rich manganese-based cathode material provided by this invention does indeed form a one-dimensional linear structure through the self-assembly of active particles; and each active particle has a double core-shell structure, with an outer shell of carbon, an intermediate layer of spinel phase, and a core of layered material. In contrast, in Comparative Example 1, the intermediate layer was not formed because the amount of lithium source was not within the range required by this invention. In Comparative Example 2, the calcination mechanism was not within the range required by this invention, and the temperature of the second calcination stage was insufficient (<800℃), which limited the growth of the spinel intermediate layer, resulting in insufficient lithium-ion diffusion motive force and the inability to form a continuous spinel heterolayer on the surface of the layered core. Furthermore, the crystallinity of the layered phase core was low.

[0145] The fifth aspect of this example tests the electrochemical performance of the lithium-ion battery obtained in the application example, reflecting the electrochemical performance of the lithium-rich manganese-based cathode materials obtained in the examples and comparative examples. The rate testing method involves conducting electrochemical tests within a voltage range of 2.0–4.8 V and charge / discharge conditions from 0.2C to 10C. The cycle testing method involves performing 400 cycles at a rate of 1C (or 0.1C) within a voltage range of 2.0–4.8 V, and calculating the capacity retention after 400 cycles (or 50 cycles). The capacity testing method involves testing the charge / discharge specific capacity in the first cycle at a rate of 0.1C within a voltage range of 2.0–4.8 V. The lithium-ion diffusion coefficient is tested using GITT (giant current intermittent titration), with a pulse current rate of 0.1C, a pulse duration of 20 min, and a relaxation time of 40 min. In this example, the current density was set to 1C = 250mA / g; all coin cell tests were conducted after two weeks of 0.1C activation, starting from the third week.

[0146] Test results show that, due to the lack of a spinel phase interlayer in Comparative Example 1, the rate performance of the lithium-rich manganese-based cathode material is inferior to that of materials SL-LMNCO-1 and SL-LMNCO-2. Specific test results are as follows... Figure 5 As shown.

[0147] Comparing the specific capacity of the lithium-rich manganese-based cathode materials obtained in Example 1 and Comparative Example 2, it can be seen that the specific capacity of Comparative Example 2 is low due to the lack of an intermediate layer and poor core crystallinity, resulting in fewer lithium storage sites. The first-cycle charge-discharge specific capacity of sample SL-LMNCO-1 in Example 1 at a current density of 0.1C is higher than that of sample LMNCO-1 in Comparative Example 2, and it exhibits higher anion oxygen activity (corresponding to a plateau at charging potential > 4.5V). A spinel phase discharge plateau corresponding to sample SL-LMNCO-1 in Example 1 can be observed at the discharge potential of ~2.6V, while this corresponding spinel phase discharge plateau is not present in sample LMNCO-1 in Comparative Example 2. Specific test results are as follows... Figure 8 As shown.

[0148] Comparing the cycling results of Examples 1 and 2 with Comparative Example 1, it can be seen that under 1C conditions, the initial cycling capacities of Examples 1, 2, and 1 are 210.7 mAh / g, 183.1 mAh / g, and 157.2 mAh / g, respectively, and their specific capacities after 400 cycles are 189.7 mAh / g, 162.6 mAh / g, and 133.2 mAh / g, respectively. Among them, the sample SL-LMNCO-1 in Example 1 maintained a capacity retention of 90% after 400 cycles at a current density of 1C. Specific test results are as follows... Figure 6 As shown.

[0149] Under 0.1C conditions, the lithium-ion diffusion coefficients of three lithium-rich manganese-based cathode materials (Examples 1, 2, and Comparative Example 1) were calculated using GITT curves. Among them, the lithium-ion diffusion coefficient of sample SL-LMNCO-1 in Example 1 ranged from 10... -10.3 ~10 -8.9 cm 2 / s, the lithium-ion diffusion coefficient of SL-LMNCO-2 is in the range of 10. -11.9 ~10 -9.8 cm 2 / s, the lithium-ion diffusion coefficient of LMNCO is in the range of 10. -12.9 ~10 -9.6 cm 2 / s. Specific test results are as follows: Figure 7 As shown.

[0150] The test results of Example 1 and Comparative Example 2 show that the discharge specific capacity of sample SL-LMNCO-1 in Example 1 at a current density of 0.1C is 311.7 mAh / g in the first cycle and 243.7 mAh / g after 50 cycles; the discharge specific capacity of sample LMNCO-1 in Comparative Example 2 at a current density of 0.1C is 222.9 mAh / g in the first cycle and 150.7 mAh / g after 50 cycles. Specific test results are as follows... Figures 8-9 As shown.

[0151] Compared to Example 1, the cycling performance at lower rates is worse. This is because lithium-rich manganese-based cathode materials are different from other types of cathode materials. The capacity of lithium-rich manganese-based cathode materials is contributed by the valence changes of anions and cations. At low rates, the valence change reaction of anions / cations is more complete, which makes it easier to cause a structural phase transition (loss of anionic oxygen) in lithium-rich materials under the condition of fully utilizing high capacity, thereby causing capacity decay and a relatively lower capacity retention rate.

[0152] The above electrochemical results are listed in Table 1.

[0153] Table 1 Electrochemical performance results of the examples and comparative examples

[0154]

[0155] The above electrochemical performance tests demonstrate that the lithium-rich manganese-based cathode material with a special structure and composition prepared using the method provided by this invention exhibits excellent performance in terms of electrochemical cycling, capacity, and rate capability. Due to these advantages, lithium-ion batteries, including those using the aforementioned lithium-rich manganese-based cathode material, are expected to find wide application in the fields of power batteries, energy storage batteries, and electronic communications.

[0156] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for preparing a lithium-rich manganese-based cathode material, characterized in that, The preparation method includes the following steps: S1. The transition metal source of the layered lithium-rich manganese material was mixed and dispersed with hyponitrotriacetic acid and then subjected to a solvothermal reaction to obtain the first precursor. S2. The first precursor and the lithium source are mixed according to the molar ratio of lithium:metal = 1.05~1.20:0.8 to obtain the second precursor; S3. Calcining the second precursor in an oxygen-containing atmosphere; The calcination includes a first stage of calcination and a second stage of calcination performed sequentially. The calcination temperature of the first stage is 300~500℃; The calcination temperature in the second stage is 800~900℃; The lithium-rich manganese-based cathode material is assembled from active particles and has a one-dimensional linear structure. The active particles have a double core-shell structure, wherein the core is a layered lithium-rich manganese material, and the middle layer includes spinel-type Li4Mn5O. 12 The outer shell is a carbon layer.

2. The preparation method according to claim 1, characterized in that, The thickness of the intermediate layer is 2~20nm.

3. The preparation method according to claim 1, characterized in that, The thickness of the outer shell layer is 2~5nm; And / or, the material of the carbon layer includes amorphous carbon.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The particle size of the active particles is 80~120nm.

5. The preparation method according to any one of claims 1 to 3, characterized in that, The chemical formula of the core is Li 1.2 M 0.8 O2; and M includes Mn.

6. The preparation method according to claim 1, characterized in that, In step S1, the temperature of the solvothermal reaction is 150–200°C; and / or, in step S1, the first precursor has a one-dimensional linear structure.

7. The preparation method according to claim 1, characterized in that, In step S2, the mixing includes wet mixing.

8. The preparation method according to claim 1, characterized in that, In step S3, the duration of the first calcination stage is 5 to 10 hours; and / or, in step S3, the duration of the second calcination stage is 10 to 20 hours.

9. A lithium-ion battery, characterized in that, The raw materials for preparing the lithium-ion battery include lithium-rich manganese-based cathode materials prepared by the preparation method according to any one of claims 1 to 8.

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