A fast-charging spinel lithium manganese oxide cathode material, its preparation method and application

Abstract

This application provides a fast-charging spinel lithium manganese oxide cathode material, its preparation method, and its application, belonging to the field of lithium battery technology. The material includes spinel lithium manganese oxide matrix particles, a first dopant element M distributed within the lithium manganese oxide matrix, the concentration of the first dopant element M decreasing monotonically from the particle center to the surface; and a wrinkled graphene conductive layer coating the surface of the lithium manganese oxide matrix particles; wherein the wrinkled graphene conductive layer is composed of single or multiple graphene sheets, the graphene sheets deforming and tightly adhering to the smooth surface of the lithium manganese oxide matrix particles, forming bridges between adjacent particles; the first dopant element M is selected from one or more of Al, Mg, Ti, and Zr. This application successfully prepares a spinel lithium manganese oxide cathode material with high specific capacity and good cycle stability through elemental doping, showing broad application prospects.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a fast-charging spinel lithium manganese oxide cathode material, its preparation method and application. Background Technology

[0002] Lithium spinel manganese oxide (LiMn2O4) is considered one of the important cathode materials in the field of power and energy storage batteries due to its advantages such as three-dimensional lithium-ion diffusion channels, high operating voltage (~4.0V vs. Li+ / Li), abundant raw materials, low cost, and environmental friendliness. However, its commercial application, especially in high-rate charge-discharge scenarios, is mainly limited by two inherent defects: 1) the dissolution of manganese, especially in high-temperature and acidic electrolyte environments, leading to loss of active material and structural collapse; 2) poor electronic conductivity and insufficient lithium-ion diffusion kinetics at high rates, resulting in limited power density and rapid capacity decay.

[0003] To address these challenges, existing technologies primarily focus on bulk doping and surface coating. For example, CN101807682B discloses improving cycle performance by doping with elements such as Nb and Al combined with LiAlO2 coating. CN118198342A improves rate performance by preparing single-crystal high-voltage lithium nickel manganese oxide. These methods improve the stability or ion diffusion capability of materials to some extent, but they often come at the cost of other aspects: while bulk doping can stabilize the structure, it may introduce ion diffusion barriers; while inert oxide coating can suppress interfacial side reactions, it can hinder electron and ion transport, which is detrimental to rate performance.

[0004] Therefore, developing a comprehensive modification strategy that can simultaneously and synergistically address the bulk structural stability, interfacial chemical stability, ion diffusion kinetics, and electronic conductivity of spinel lithium manganese oxide is crucial for its breakthrough application in high-power batteries. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a fast-charging spinel lithium manganese oxide cathode material, its preparation method and application.

[0006] Specifically, the first aspect of this application provides a fast-charging spinel lithium manganese oxide cathode material, wherein the material has a core-shell composite structure, comprising:

[0007] Lithium manganese oxide matrix particles with spinel structure

[0008] The first dopant element M is distributed inside the lithium manganese oxide matrix, and the concentration of the first dopant element M decreases monotonically from the particle center to the surface.

[0009] And a wrinkled graphene conductive layer coated on the surface of the lithium manganese oxide matrix particles;

[0010] The wrinkled graphene conductive layer is composed of a single layer or multiple layers of graphene sheets. The graphene sheets deform and adhere tightly to the smooth surface of the lithium manganese oxide matrix particles, and form bridges between adjacent particles.

[0011] The first dopant element M is selected from one or more of Al, Mg, Ti, and Zr.

[0012] Furthermore, the primary particle size of the lithium manganese oxide matrix particles is 50-500 nm, and the surface exhibits a smooth polyhedral morphology without chemically etched pores with a depth exceeding 5 nm.

[0013] Furthermore, the thickness of the wrinkled graphene conductive layer is 2-15 nm, and the carbon content accounts for 0.8%-2.5% of the total mass of the material.

[0014] Furthermore, the primary particles of the lithium manganese oxide matrix particles exhibit a regular polyhedral morphology, and the average particle size D50 of the lithium manganese oxide matrix particles is 50 nm to 500 nm.

[0015] And / or, in the X-ray diffraction pattern of the lithium manganese oxide matrix particles, the ratio of the diffraction peak intensity of the (111) crystal plane to that of the (400) crystal plane is I(111) / I(400)≤2.5;

[0016] And / or, the graphene sheet is anchored to the surface of the polyhedron by van der Waals forces and local CO-Mn bonding, and maintains a complete layered crystal structure after high-temperature sintering above 700°C, with an amorphous carbon impurity content of less than 10%.

[0017] Furthermore, the surface of the lithium manganese oxide matrix particles is also distributed with trace amounts of non-metallic modifying element Z, wherein element Z is selected from one or more of P, F, and B;

[0018] The element Z exists in the form of an amorphous oxide or salt at the interface between the lithium manganese oxide substrate and the wrinkled graphene conductive layer, which enhances the interfacial bonding force and inhibits the dissolution of manganese ions at high temperatures.

[0019] Furthermore, the content of element Z is 0.1-0.5 wt% of the lithium manganese oxide matrix particles.

[0020] A second aspect of this application provides a method for preparing a fast-charging spinel lithium manganese oxide cathode material, comprising the following steps:

[0021] Step S1: Manganese-based precursor particles with a concentration gradient of doping element M are prepared by liquid-phase precipitation.

[0022] Step S2: Disperse the precursor particles obtained in step S1 in an aqueous dispersion of graphene oxide, and then spray dry or freeze dry to uniformly coat the surface of the precursor with graphene oxide sheets to form a precursor@graphene oxide composite.

[0023] Step S3: Place the precursor@graphene oxide composite in a tube furnace and heat it to 800-850°C at a rate of 4-6°C / min, and hold it at that temperature for 10-12 hours.

[0024] Subsequently, under an inert atmosphere, the temperature was increased to 450-550℃ at a heating rate of 2-3℃ / min and sintered for 2-4 hours.

[0025] During this process, the precursor is transformed into spinel lithium manganese oxide with a gradient doping structure, while graphene oxide is reduced in situ to well-crystallized graphene, forming a wrinkled conductive layer that is tightly attached to the substrate surface.

[0026] Furthermore, in step S1, the reaction temperature of the liquid-phase precipitation method is controlled at 45-55℃, and the pH value is controlled at 7.5-8.0.

[0027] Further, in step S3, the inert atmosphere is a N2 / H2 mixture with a volume ratio of 95:5-99:1, or high-purity Ar gas;

[0028] After sintering, the graphene layer is cooled to room temperature naturally to prevent it from peeling off due to sudden changes in thermal stress.

[0029] Further, in step S2, the concentration of the graphene oxide aqueous dispersion is 0.5-1.0 mg / mL, and the pH value is adjusted to 3.5-4.5. The negatively charged graphene oxide sheets are uniformly adsorbed on the positively charged precursor surface by electrostatic adsorption.

[0030] And / or, the inlet temperature of the spray dryer is 170-190°C, and the outlet temperature is 80-100°C.

[0031] Furthermore, step S2 also includes adding a trace amount of phosphorus or fluorine source to the graphene oxide aqueous dispersion, so that the content of non-metallic modification element Z at the interface in the final product is controlled at 0.1-0.5 wt%.

[0032] The third aspect of this application provides an application of the fast-charging spinel lithium manganese oxide cathode material in lithium-ion batteries.

[0033] The present invention has the following beneficial effects:

[0034] This invention achieves a significant improvement in the overall performance of spinel lithium manganese oxide cathode materials through the synergistic effect of gradient doping design and wrinkled graphene coating. The first dopant element M in the gradient doping exhibits a monotonically decreasing distribution from the particle center to the surface, which reduces the obstruction to lithium-ion diffusion at the particle surface while ensuring bulk structural stability. The high concentration of M at the center can suppress Jahn-Teller distortion by strengthening the Mn-O bond energy, thus improving structural stability; while the low concentration of M at the surface avoids the formation of excessively high potential barriers at the lithium-ion diffusion channel inlet, which is beneficial for maintaining a high ion diffusion rate, thereby balancing the material's cycle stability and high-rate performance.

[0035] The wrinkled graphene conductive layer, composed of single or multiple layers of graphene sheets, conforms to the smooth surface of the lithium manganese oxide substrate particles, deforming and adhering tightly to them. This ensures good contact between the conductive layer and the substrate, reducing interfacial resistance. Simultaneously, the graphene bridging network formed between adjacent particles significantly improves the overall electronic conduction path of the material, effectively enhancing the electronic conductivity of the electrode, which is crucial for achieving high-rate fast charging.

[0036] The first dopant element M is selected from one or more of Al, Mg, Ti, and Zr, and the ionic radii of these elements are similar to those of Mn. 3+ / Mn 4+ It is a good match and can effectively enter the spinel lattice, stabilizing the crystal structure. Among them, Al 3+ and Mg 2+ Alkaline earth or rare earth metals can suppress manganese dissolution and structural collapse through valence compensation and lattice support; Ti 4+ and Zr 4+ High-valence ions enhance structural rigidity, further improving the material's stability during cycling. This synergistic design of gradient doping and wrinkled graphene coating successfully solves the problem of balancing structural stability and electron-ion conductivity in traditional spinel lithium manganese oxide under high-rate charge-discharge conditions, laying the foundation for the preparation of fast-charging cathode materials with high specific capacity and long cycle life. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of this drawing or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this drawing. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0038] Figure 1 This is a SEM image of the spinel lithium manganese oxide matrix particles in Example 1;

[0039] Figure 2 Here is a SEM image of the spinel lithium manganese oxide matrix particles in Example 2;

[0040] Figure 3 This is a SEM image of the graphene-coated shell in Example 1;

[0041] Figure 4 This is a SEM image of the graphene-coated shell in Example 2;

[0042] Figure 5 This is a comparison of the XRD patterns of Example 1 and Comparative Example 1.

[0043] The purpose, features, and advantages of this accompanying drawing will be further explained in conjunction with the embodiments and with reference to the accompanying drawing. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0045] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0046] An embodiment of the first aspect of this application provides a fast-charging spinel lithium manganese oxide cathode material, the material comprising:

[0047] Lithium manganese oxide matrix particles with spinel structure

[0048] The first dopant element M is distributed inside the lithium manganese oxide matrix, and the concentration of the first dopant element M decreases monotonically from the particle center to the surface.

[0049] And a wrinkled graphene conductive layer coated on the surface of the lithium manganese oxide matrix particles;

[0050] The wrinkled graphene conductive layer is composed of a single layer or multiple layers of graphene sheets. The graphene sheets deform and adhere tightly to the smooth surface of the lithium manganese oxide matrix particles, and form bridges between adjacent particles.

[0051] The first dopant element M is selected from one or more of Al, Mg, Ti, and Zr.

[0052] The primary particle size of the lithium manganese oxide matrix particles in the material is 50-500 nm, and the surface exhibits a smooth polyhedral morphology without chemically etched pores deeper than 5 nm. This regular morphology helps to improve the packing density and structural stability of the material. The thickness of the wrinkled graphene conductive layer is 2-15 nm, and the carbon content accounts for 0.8%-2.5% of the total mass of the material. This thickness range can ensure a good conductive network construction without excessively increasing the volume of the material or affecting the diffusion of lithium ions. The primary particles of the lithium manganese oxide matrix particles exhibit a regular polyhedral morphology, and their average particle size D50 is 50 nm to 500 nm. In the X-ray diffraction pattern of the lithium manganese oxide matrix particles, the ratio of the diffraction peak intensity of the (111) crystal plane to that of the (400) crystal plane is ≤2.5, which indicates that the material has a specific crystal orientation and good crystallinity. The graphene sheets are anchored to the polyhedral surface through van der Waals forces and localized CO-Mn bonds, and maintain a complete layered crystal structure even after sintering at temperatures above 700°C. The amorphous carbon impurity content is less than 10%, ensuring the structural integrity and high conductivity of the conductive layer. Furthermore, trace amounts of the non-metallic modifying element Z are distributed on the surface of the lithium manganese oxide matrix particles. Element Z is selected from one or more of P, F, and B, existing as an amorphous oxide or salt at the interface between the lithium manganese oxide matrix surface and the wrinkled graphene conductive layer. The content of element Z is 0.1-0.5 wt% of the lithium manganese oxide matrix particles, serving to enhance interfacial bonding and inhibit the dissolution of manganese ions at high temperatures.

[0053] A second aspect of the present invention provides a method for preparing a fast-charging spinel lithium manganese oxide cathode material, comprising the following steps:

[0054] Step S1: Manganese-based precursor particles with a concentration gradient of doping element M are prepared by liquid-phase precipitation.

[0055] Step S2: Disperse the precursor particles obtained in step S1 in an aqueous dispersion of graphene oxide, and then spray dry or freeze dry to uniformly coat the surface of the precursor with graphene oxide sheets to form a precursor@graphene oxide composite.

[0056] Step S3: Place the precursor@graphene oxide composite in a tube furnace and heat it to 800-850°C at a rate of 4-6°C / min, and hold it at that temperature for 10-12 hours.

[0057] Subsequently, under an inert atmosphere, the temperature was increased to 450-550℃ at a heating rate of 2-3℃ / min and sintered for 2-4 hours.

[0058] During this process, the precursor is transformed into spinel lithium manganese oxide with a gradient doping structure, while graphene oxide is reduced in situ to well-crystallized graphene, forming a wrinkled conductive layer that is tightly attached to the substrate surface.

[0059] Specifically, step S1, gradient precursor preparation: a dual-pump continuous co-precipitation method was used. Pump A delivered a 0.5-1.0 mol / L mixed solution containing MnSO4 and Al2(SO4)3, with the Al / Mn molar ratio controlled at 0.1-0.2; pump B delivered a 0.5-1.0 mol / L pure MnSO4 solution. The reaction temperature was controlled at 45-55℃, and the pH value was controlled at 7.5-8.0. At the beginning of the reaction, the flow rate of pump A accounted for 90%, decreasing linearly to 10% over time, and at the end of the reaction, the flow rate of pump B accounted for 90%. The precipitant was a mixture of NH4HCO3 / NH3·H2O. After filtration and washing three times with deionized water, the sample was dried at 100℃ for 12 hours. A spherical precursor with a monotonically decreasing M element concentration from the center to the surface was obtained.

[0060] S2. Preparation of graphene oxide (GO) dispersion: Disperse GO powder in deionized water and sonicate for 2 hours to obtain a uniform dispersion with a concentration of 1.0 mg / mL; weigh lithium salt and lithium hydroxide in stoichiometric proportions, and control the Li / Mn molar ratio at 1.03-1.05 considering high-temperature volatilization; dissolve or disperse the lithium salt directly in the above GO aqueous dispersion; adjust the pH to 3.5-4.5 with dilute hydrochloric acid to facilitate subsequent adsorption using electrostatic interaction.

[0061] In another preferred embodiment, a trace amount of phosphorus or fluorine source is added to the graphene oxide aqueous dispersion. Specifically, ammonium dihydrogen phosphate (NH4H2PO4) or ammonium fluoride (NH4F) is added to the graphene oxide aqueous dispersion at a concentration of 0.05-0.2 g / L, and the mixture is ultrasonically stirred for 30 minutes to ensure uniform dispersion. The addition of the phosphorus or fluorine source allows phosphorus or fluorine elements to migrate to the interface between the lithium manganese oxide matrix and the graphene layer during the subsequent sintering process, existing as amorphous lithium phosphate or lithium fluoride, thereby achieving effective modification of the interface.

[0062] Composite and spray drying: The precursor obtained in S1 (after washing and drying) was added to the GO-lithium source dispersion in S2 at a solid-liquid ratio of 1:10, and stirred at high speed (10000 rpm) for 1 hour. At this time, the negatively charged GO flakes and lithium / hydroxyl ions will uniformly adhere to the positively charged manganese-based precursor surface through electrostatic adsorption and physical deposition. Subsequently, spray drying was performed (inlet temperature 170-190℃, outlet temperature 80-100℃) to obtain the precursor@GO composite.

[0063] S3. In-situ reduction sintering under protected atmosphere: The composite is placed in a tube furnace and heated to 800-850℃ at 5℃ / min, held for 10-12 hours, and then cooled to room temperature with the furnace to ensure the ordered arrangement of Li / Mn, forming a perfect spinel structure, allowing the gradient dopant element M to fully enter the lattice. The resulting LMO particles are coated with graphene oxide (GO). Subsequently, a N2 / H2 (95:5) mixed gas is introduced, and the temperature is increased to 450-550℃ at 2-3℃ / min, held for sintering for 2-4 hours. Within this temperature range, GO loses oxygen-containing functional groups and transforms into conductive graphene, while the generated gas leads to the formation of interlayer wrinkles; the remaining small amount of oxygen-containing groups form CO-Mn bonds with Mn on the LMO surface. A P / F source is added, forming an amorphous interface layer.

[0064] The third aspect of this application provides an application of the fast-charging spinel lithium manganese oxide cathode material in lithium-ion batteries.

[0065] Example

[0066] The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.

[0067] Example 1

[0068] A method for preparing a fast-charging spinel lithium manganese oxide cathode material includes the following steps:

[0069] Step S1, Gradient Precursor Preparation: A dual-pump continuous co-precipitation method was used. Pump A delivered a 1.0 mol / L mixed solution containing MnSO4 and Al2(SO4)3, with the Al / Mn molar ratio controlled at 0.15; Pump B delivered a 1.0 mol / L pure MnSO4 solution. The reaction temperature was controlled at 50℃, and the pH value was controlled at 7.8. At the beginning of the reaction, the flow rate of pump A was 90%, which decreased linearly to 10% over time, and at the end of the reaction, the flow rate of pump B was 90%. The precipitant was a mixture of NH4HCO3 / NH3·H2O. After the reaction, the mixture was filtered, washed three times with deionized water, and dried at 100℃ for 12 hours. A spherical precursor with a monotonically decreasing M element concentration from the center to the surface was obtained. The morphology of the lithium manganese oxide matrix particles is shown in the figure. Figure 1 .

[0070] S2. Preparation of graphene oxide (GO) dispersion: 2.92g of GO powder was dispersed in 2000mL of deionized water and pre-dispersed for 30 minutes under magnetic stirring at 300rpm. The dispersion was then sonicated at 400W for 2 hours to obtain a uniform dispersion with a concentration of 1.0mg / mL. 24.5g of lithium hydroxide was weighed, and the Li / Mn molar ratio was controlled at 1.05. The lithium salt was directly dissolved in the GO aqueous dispersion. The mixture was stirred for 30 minutes until the lithium salt was completely dissolved. The pH was adjusted to 4.0 with dilute hydrochloric acid to obtain the GO-lithium source dispersion.

[0071] Composite and spray drying: 100g of the precursor obtained from S1 was added to the GO-lithium source dispersion of S2 at a solid-liquid ratio of 1:10, and the mixture was stirred at high speed (10000rpm) for 1 hour. Subsequently, spray drying was performed at an inlet temperature of 180℃ and an outlet temperature of 90℃ to obtain the precursor@GO composite.

[0072] S3. In-situ reduction sintering under protected atmosphere: The composite was placed in a tube furnace and heated to 820°C at 5°C / min, and held for 10 hours; then, a N2 / H2 (95:5) mixed gas was introduced and heated to 5000°C at 3°C / min, and sintered for 3 hours to form a graphene conductive layer. The morphology is shown in the figure. Figure 3 The graphene content was 1.5 wt% after furnace cooling.

[0073] Example 2

[0074] This embodiment is basically the same as Embodiment 1, except that the doping element in solution A of step S1 is changed to Mg, and the Al / Mn molar ratio is controlled at 0.12; the morphology of the lithium manganese oxide matrix particles is shown in the figure. Figure 2 The morphology diagram of the graphene conductive layer is shown below. Figure 4 .

[0075] Example 3

[0076] This embodiment is basically the same as embodiment 1, except that in step S2, 2.92g of GO powder is dispersed in 2000mL of deionized water to make the graphene content in the lithium manganese oxide cathode material 0.8wt%.

[0077] Example 4

[0078] This embodiment is basically the same as that of embodiment 1, except that in step S2, 4.91g of GO powder is dispersed in 2000mL of deionized water to make the graphene content in the lithium manganese oxide cathode material 2.5wt%.

[0079] Example 5

[0080] This embodiment is basically the same as that of embodiment 1, except that in step S2, when preparing the graphene oxide dispersion, 0.1 g / L of ammonium dihydrogen phosphate (NH4H2PO4) is added and ultrasonically stirred for 30 minutes to make it uniformly dispersed.

[0081] Comparative Example 1

[0082] This comparative example is basically the same as Example 1, except that in step S1, only manganese sulfate is used as the metal source, and no aluminum source or other dopants are added. Pure MnCO3 precursor is prepared by co-precipitation.

[0083] Comparative Example 2

[0084] This comparative example is basically the same as Example 1, except that graphene oxide is not used in step S2. 4.75g of glucose is used as the carbon source, glucose is dissolved in deionized water, LiOH is added, the pH is adjusted to 4.0, and then mixed with the precursor.

[0085] Comparative Example 3

[0086] This comparative example is basically the same as Example 1, except that in step S1, manganese sulfate and aluminum sulfate are prepared into a single mixed solution by molar ratio Mn:Al=1:0.03; the mixed solution and precipitant (NH4HCO3 / NH3·H2O) are added to the reactor in parallel flow, the pH is controlled at 7.5, the temperature is 50°C, the reaction is stirred for 12 hours, and after washing and drying, a manganese carbonate precursor with uniform Al element distribution is obtained.

[0087] Comparative Example 4

[0088] This comparative example is basically the same as Example 1, except that the atmosphere of the sintering furnace in step S3 is changed from N2 / H2 mixture to ordinary air.

[0089] Experimental Case 1:

[0090] The lithium manganese oxide cathode materials obtained in the examples and comparative examples were assembled into CR2032 coin cells for electrochemical performance testing. A lithium metal sheet was used as the negative electrode, and a Celgard 2400 polypropylene microporous membrane was used as the separator. The electrolyte was 1 mol / L LiPF6 (EC:DEC = 1:1, v / v). The cathode, negative electrode, separator, and electrolyte were assembled in an argon glove box with a water and oxygen content of less than 1 ppm. After assembly, the cells were allowed to stand for 24 hours to obtain the battery. Under charge / discharge cutoff voltages of 3.0-4.3V, the discharge specific capacity (mAh / g) at different rates (0.2C, 5C) and the capacity retention at 5C were tested; the conductivity (S / cm) was also tested. The test results are shown in Table 1.

[0091]

[0092] As shown in Table 1, the fast-charging spinel lithium manganese oxide cathode materials prepared in Examples 1-5 exhibited significant advantages in various electrochemical performance tests. For example, Example 1 achieved a specific capacity of 125.8 mAh / g in the first cycle at 0.2C and 112.2 mAh / g in the first cycle at 5C, demonstrating excellent high-rate discharge capability; its 5C cycle capacity retention rate was 89.2%, and the charge transfer resistance Rct after 500 cycles was only 45Ω, with a retention rate as high as 91.5% after 500 cycles at 55℃. Example 5, through interface modification by introducing phosphorus, further improved performance, increasing the specific capacity in the first cycle at 5C to 114.1 mAh / g, achieving a 5C capacity retention rate of 90.3%, and a 55℃ cycle retention rate of 93.2%, while reducing Rct to 40Ω, indicating that the modification with non-metallic element Z effectively enhanced interface stability and reduced charge transfer resistance.

[0093] In contrast, Comparative Example 1, which did not contain any dopants, had a high specific capacity at 5C (115.2 mAh / g) but only a 58.1% retention rate after 500 cycles at 55°C. This indicates that pure spinel lithium manganese oxide suffers from more severe dissolution and migration of manganese ions under high-temperature conditions, resulting in poor lattice structure stability and a significant decrease in cycling performance.

[0094] Comparative Example 2 did not use graphene oxide, but only glucose as a carbon source. Its 5C first-cycle specific capacity was only 92.0 mAh / g, and the capacity retention rate was as low as 74.7%. This is because the carbon layer formed by the pyrolysis of glucose usually has poor conductivity and uneven coating, and cannot build an efficient three-dimensional conductive network like wrinkled graphene. This leads to increased electron transport resistance of the material and poor electrochemical performance during high-rate charge and discharge.

[0095] Comparative Example 3, employing uniform doping rather than gradient doping, achieved a 5C capacity retention of 84.3%. This may be because uniform doping cannot create an elemental concentration gradient from the center to the surface within the material, unlike gradient doping, making it difficult to specifically optimize the performance of different regions. Excessive doping in the central region can lead to excessive structural rigidity, while insufficient doping in the surface region cannot effectively suppress interfacial side reactions. Consequently, during long-term cycling, the material structure is prone to damage due to stress concentration and interfacial instability, resulting in accelerated capacity decay.

[0096] Comparative Example 4, sintering in air, makes it difficult for graphene oxide to be effectively reduced to highly conductive graphene. Instead, it may form more defects due to oxidation, resulting in a decrease in the material's conductivity (the charge transfer resistance Rct reaches as high as 120Ω after 500 cycles), which in turn affects its fast charging performance and cycle stability.

[0097] These comparative results strongly demonstrate the synergistic effect of the gradient doping, wrinkled graphene coating, and interface modification techniques employed in this invention, which significantly improve the overall performance of the prepared spinel lithium manganese oxide cathode material.

[0098] Experimental Case 2

[0099] X-ray diffraction (XRD) was performed on the lithium manganese oxide matrix particles of Example 1 and Comparative Example 1. The XRD patterns showed a pure-phase spinel structure (space group Fd-3m), and the ratio of the diffraction peak intensity of the (111) crystal plane to that of the (400) crystal plane, I(111) / I(400), was ≤2.5, indicating that the growth of the (111) crystal plane was suppressed. The results are shown in […]. Figure 5 And Table 2.

[0100]

[0101] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A fast-charging spinel lithium manganate cathode material, characterized in that, include: The lithium manganese oxide matrix particles have a spinel structure, wherein the primary particles of the lithium manganese oxide matrix particles exhibit a regular polyhedral morphology, and the average particle size D50 of the lithium manganese oxide matrix particles is 50 nm to 500 nm. The first dopant element M is distributed within the lithium manganese oxide matrix, and the concentration of the first dopant element M decreases monotonically from the particle center to the surface; the first dopant element M is selected from one or more of Al, Mg, Ti, and Zr. And a wrinkled graphene conductive layer coated on the surface of the lithium manganese oxide matrix particles; the thickness of the wrinkled graphene conductive layer is 2-15 nm, and the carbon content accounts for 0.8%-2.5% of the total mass of the material; The wrinkled graphene conductive layer is composed of a single layer or multiple layers of graphene sheets. The graphene sheets deform and adhere tightly to the smooth surface of the lithium manganese oxide matrix particles, and form bridges between adjacent particles. The graphene sheets are anchored to the surface of the polyhedron through van der Waals forces and local CO-Mn bonding, and maintain a complete layered crystal structure after sintering at temperatures above 700°C, with amorphous carbon impurities content of less than 10%; the surface of the lithium manganese oxide matrix particles is also distributed with a non-metallic modifying element Z accounting for 0.1-0.5 wt% of the lithium manganese oxide matrix particles, wherein the element Z is selected from one or more of P and F; The element Z exists in the form of an amorphous oxide or salt at the interface between the lithium manganese oxide substrate and the wrinkled graphene conductive layer, which enhances the interfacial bonding force and inhibits the dissolution of manganese ions at high temperatures.

2. The fast-charging spinel lithium manganese oxide cathode material according to claim 1, characterized in that, In the X-ray diffraction pattern of the lithium manganese oxide matrix particles, the ratio of the diffraction peak intensity of the (111) crystal plane to that of the (400) crystal plane is I(111) / I(400)≤2.

5.

3. A method for preparing a fast-charging spinel lithium manganese oxide cathode material, characterized in that, The preparation of the fast-charging spinel lithium manganese oxide cathode material according to any one of claims 1-2 includes the following steps: Step S1: Manganese-based precursor particles with a concentration gradient of doping element M are prepared by liquid-phase precipitation. Step S2: Disperse the precursor particles obtained in step S1 in an aqueous dispersion of graphene oxide, and add a phosphorus source or a fluorine source to the aqueous dispersion of graphene oxide so that the content of the non-metallic modification element Z at the interface in the final product accounts for 0.1-0.5 wt% of the lithium manganese oxide matrix particles; by spray drying or freeze drying, make the graphene oxide sheets uniformly coat the surface of the precursor to form a precursor@graphene oxide composite. Step S3: Place the precursor@graphene oxide composite in a tube furnace and heat it to 800-850°C at a rate of 4-6°C / min, and hold it at that temperature for 10-12 hours. Subsequently, under an inert atmosphere, the temperature was increased to 450-550℃ at a heating rate of 2-3℃ / min and sintered for 2-4 hours. During this process, the precursor is transformed into spinel lithium manganese oxide with a gradient doping structure, while graphene oxide is reduced in situ to well-crystallized graphene, forming a wrinkled conductive layer that is tightly attached to the substrate surface.

4. The preparation method of the fast-charging spinel lithium manganese oxide cathode material according to claim 3, characterized in that, The reaction temperature of the liquid-phase precipitation method described in step S1 is controlled at 45-55℃, and the pH value is controlled at 7.5-8.

0.

5. The preparation method of the fast-charging spinel lithium manganese oxide cathode material according to claim 3, characterized in that, In step S3, the inert atmosphere is a N2 / H2 mixture with a volume ratio of 95:5-99:1, or high-purity Ar gas; After sintering, the graphene layer is cooled to room temperature naturally to prevent it from peeling off due to sudden changes in thermal stress.

6. The preparation method of the fast-charging spinel lithium manganese oxide cathode material according to claim 3, characterized in that, In step S2, the concentration of the graphene oxide aqueous dispersion is 0.5-1.0 mg / mL, and the pH value is adjusted to 3.5-4.

5. The negatively charged graphene oxide sheets are uniformly adsorbed on the positively charged precursor surface by electrostatic adsorption. And / or, the inlet temperature of the spray dryer is 170-190°C, and the outlet temperature is 80-100°C.

7. The application of a fast-charging spinel lithium manganese oxide cathode material as described in any one of claims 1-2 or a fast-charging spinel lithium manganese oxide cathode material prepared by the method described in claim 3 in a lithium-ion battery.

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