Manganese-based composite negative electrode material, negative electrode plate, preparation methods of manganese-based composite negative electrode material and negative electrode plate, and lithium ion battery

Abstract

The invention discloses a manganese-based composite negative electrode material, a negative electrode plate, preparation methods of the manganese-based composite negative electrode material and the negative electrode plate, and a lithium ion battery. The manganese-based composite negative electrode material is a composite material of manganous-manganic oxide and reduced graphene oxide. In the negative electrode material provided by the invention, the graphene matrix provides a conductive three-dimensional network structure for Mn3O4, the Mn3O4 nano octahedron prevents the graphene layer from being stacked again, and in addition, the Mn3O4 nano structure wrapped by graphene can reduce volume expansion in the charging and discharging process, so that the cycle life is prolonged.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a manganese-based composite anode material, anode sheet, their preparation methods, and lithium-ion batteries. Background Technology

[0002] As one of the next-generation power sources used in numerous fields, lithium-ion batteries have seen increasing demand, prompting the industry to improve their overall performance in terms of power density and energy density through various channels, such as positive and negative electrodes and electrolytes. Among these, the negative electrode material is a crucial component of the lithium-ion battery system. Taking graphite, the most commonly used negative electrode material, as an example, it features a low discharge platform and stable cycle performance, but its specific capacity of 372 mAh / g remains relatively low, and it suffers from problems such as lithium dendrite formation risk and irreversible capacity loss during the first charge-discharge cycle. Therefore, the development of novel negative electrode materials is imperative. Metal oxides have attracted considerable attention due to their abundant resources, simple preparation, and safety. Manganese oxide-based materials, especially Mn3O4, have a theoretical specific capacity as high as 936 mAh / g and possess characteristics such as low cost, abundant reserves, and environmental friendliness, making them promising negative electrode materials for lithium-ion batteries. However, this material still suffers from severe volume expansion and low conductivity. Summary of the Invention

[0003] The purpose of this invention is to provide a manganese-based composite anode material, anode sheet, their preparation methods, and a lithium-ion battery. This anode material, by combining manganese-based materials with carbon-based nanomaterials, has advantages such as high conductivity, large specific surface area, flexibility, and chemical stability.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a manganese-based composite anode material, wherein the manganese-based composite anode material is a composite material of manganese tetroxide and reduced graphene oxide.

[0005] In the aforementioned manganese-based composite anode material, the manganese tetroxide has an octahedral structure.

[0006] Secondly, the present invention provides a method for preparing a manganese-based composite anode material, comprising the following steps: The manganese-based composite anode material is obtained by mixing a dispersion containing graphene oxide with a mixture containing a manganese source and glycerol and then reacting the mixture with water via a hydrothermal reaction.

[0007] In the above preparation method, the ratio of graphene oxide to water in the dispersion containing graphene oxide is 15 mg: 30-40 mL. And / or, the preparation step of the dispersion containing graphene oxide includes ultrasonic treatment of graphene oxide and water for 15 to 25 minutes.

[0008] In the above preparation method, the manganese source is a solid powder with a purity of ≥96%; And / or, the manganese source includes one or more of potassium permanganate, manganese sulfate, and manganese chloride; And / or, the purity of the glycerol is ≥99%; And / or, in the mixture containing manganese source and glycerol, the ratio of manganese source to glycerol is 1-3 mmol: 2 mL; And / or, the mixture containing manganese source and glycerol also contains water, wherein the ratio of manganese source to water is 1–3 mmol: 40 mL; And / or, the preparation steps of the mixture containing manganese source and glycerol include dissolving manganese source in deionized water and sonicating for 15 to 25 minutes, then adding glycerol and continuing sonication for 17 to 23 minutes.

[0009] In the above preparation method, the mixing step includes ultrasonic treatment for 20 to 40 minutes.

[0010] In the above preparation method, the temperature of the hydrothermal reaction is 175-185℃; And / or, the hydrothermal reaction time is 9.5 to 10.5 hours.

[0011] Thirdly, the present invention provides a negative electrode sheet, comprising the manganese-based composite negative electrode material described in any one of the preceding claims or the manganese-based composite negative electrode material prepared by the method described in any one of the preceding claims.

[0012] Fourthly, the present invention provides a method for preparing the negative electrode sheet, comprising the following steps: The manganese-based composite negative electrode material, conductive agent, and binder are mixed in a weakly acidic dispersant, and the resulting slurry is coated onto a substrate and dried to obtain the negative electrode sheet; the weakly acidic dispersant includes any one of citric acid, tartaric acid, and malic acid.

[0013] In the above preparation method, the conductive agent includes one or more of conductive carbon black, carbon nanotubes, and graphene; And / or, the adhesive includes one or more of carboxymethyl cellulose, polyacrylic acid, and polyimide; And / or, the mass ratio of the manganese-based composite negative electrode material, the conductive agent, and the binder is (7-8):(1-2):1; And / or, the weakly acidic dispersant is added in the form of an aqueous solution with a concentration of 0.4 to 0.6 wt%; And / or, the loading of the slurry is 1.1–1.3 mg / cm³. 2 .

[0014] Fifthly, the present invention provides a lithium-ion battery comprising the manganese-based composite negative electrode material described in any one of the preceding claims, or the manganese-based composite negative electrode material prepared by the method described in any one of the preceding claims, or the negative electrode sheet described in the preceding claims, or the negative electrode sheet prepared by the method described in any one of the preceding claims.

[0015] Compared with the prior art, the technical advantages of the present invention are reflected in the following aspects: (1) The preparation method of manganese-based composite anode material (Mn3O4-rGO) for lithium-ion batteries provided by the present invention is a one-step hydrothermal method that does not require the use of any surfactants or coordination compounds. It can controllably synthesize phase-pure Mn3O4 nanostructures and their graphene composite materials. The process is simple, can be mass-produced, and has high repeatability. (2) In the negative electrode material of the present invention, the graphene matrix provides a conductive three-dimensional network structure for Mn3O4, while the Mn3O4 nano octahedrons prevent the graphene layers from being re-stacked. In addition, the graphene-encapsulated Mn3O4 nanostructure can reduce the volume expansion during the charging and discharging process, thereby extending the cycle life. (3) In the negative electrode material of the present invention, the high porosity and low diffusion resistance of the graphene matrix itself, as well as the three-dimensional interconnection with Mn3O4, all contribute to enhancing electrical conductivity and ion conductivity, and enhancing rate performance. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0017] Figure 1 This is a scanning electron microscope (SEM) image of the manganese-based composite anode material Mn3O4-rGO in Example 1 of the present invention; Figure 2 This is a scanning electron microscope (SEM) image of the manganese-based composite anode material Mn3O4-rGO in Example 2 of the present invention; Figure 3 This is a scanning electron microscope (SEM) image of the manganese-based composite anode material Mn3O4-rGO in Example 3 of the present invention; Figure 4 shows the 200-cycle electrical performance of Examples 1, 2, and 3 (coin cells prepared using the manganese-based composite negative electrode material Mn3O4-rGO from Examples 1, 2, and 3) (A) and Comparative Example 1 (coin cells prepared using pure Mn3O4 as the working electrode according to the same scheme as the examples) (B). Figure 5The EIS AC impedance Nyquist plots are for the coin cell of Example 2 and Comparative Example 1 (a coin cell prepared using pure Mn3O4 as the working electrode according to the same scheme as the example) in the performance test example 2 of the present invention. Detailed Implementation

[0018] As described in the background art, current manganese-based materials suffer from severe volume expansion and low conductivity. This invention combines manganese-based materials with carbon-based nanomaterials to reduce volume expansion during charging and discharging, further extend cycle life, enhance electrical conductivity and ion conductivity, and further improve rate performance.

[0019] In its first part, this invention provides a manganese-based composite anode material, wherein the manganese-based composite anode material is a composite material of manganese tetroxide and reduced graphene oxide.

[0020] According to embodiments of the present invention, in the manganese-based composite negative electrode material, reduced graphene oxide tightly encapsulates manganese tetroxide, which can reduce volume expansion during charge and discharge processes, thereby extending cycle life. In at least one embodiment of the present invention, the manganese tetroxide has an octahedral structure.

[0021] The second part of this invention provides a method for preparing the manganese-based composite anode material, comprising the following steps: The manganese-based composite anode material is obtained by mixing a dispersion containing graphene oxide with a mixture containing a manganese source and glycerol and then reacting the mixture with water via a hydrothermal reaction.

[0022] Based on the above technical solutions, this invention prepares a manganese tetroxide / reduced graphene oxide composite material, in which glycerol plays the following roles: 1) As a reducing agent, it drives the reaction, and the hydroxyl groups (-OH) in its molecules have reducing properties in a high-temperature hydrothermal environment (around 180°C); 2) During the process of reducing potassium permanganate to manganese tetroxide, glycerol generates KOH, and the entire hydrothermal process can maintain an alkaline environment without the need for additional alkali. Alkaline conditions are beneficial to the formation and stability of Mn3O4; 3) Glycerol molecules are small and have multiple hydroxyl groups, making it a good ligand. In the early stages of Mn3O4 crystal nucleation and growth, it can selectively adsorb onto specific crystal faces. This adsorption alters the surface energy of different crystal faces, inhibiting the growth rate of certain crystal faces, thereby guiding the crystal to grow along the thermodynamically most advantageous direction, ultimately exposing specific crystal faces and forming a regular octahedral morphology; 4) Medium regulation: the high viscosity of glycerol is beneficial for controlling growth kinetics and for the orderly arrangement of atoms, thus obtaining Mn3O4 crystals with high crystallinity and few defects; 5) Glycerol also simultaneously reduces GO, reducing the oxygen-containing functional groups on its surface and transforming it into reduced graphene oxide (rGO) with stronger conductivity. The synchronous effect and the bridging effect of glycerol molecules can help form a tightly composite encapsulated structure of Mn3O4 and graphene.

[0023] According to an embodiment of the present invention, in the dispersion containing graphene oxide, the ratio of graphene oxide to water is 15 mg: 30-40 mL, such as 15 mg: 35 mL. The preparation step of the dispersion containing graphene oxide includes ultrasonically treating graphene oxide and water for 15-25 minutes, such as 20 minutes.

[0024] According to an embodiment of the present invention, the manganese source is a solid powder with a purity of ≥96%. The manganese source includes one or more of potassium permanganate, manganese sulfate, and manganese chloride. In a specific embodiment of the present invention, using potassium permanganate as the manganese source has the following advantages: 1. The manganese source is potassium permanganate (Mn... 7+ The synthesis process is actually a strong reducing pathway, unlike the selection of manganese sources such as manganese acetate and manganese phosphate (Mn). 2+ 1. The oxidation path used; 2. Potassium permanganate is relatively easy to synthesize into a regular nano-octahedral structure: MnO4 - The highly symmetrical tetrahedral configuration of ions provides a basis for constructing octahedral structures, and the gradient reduction of multiple valence states allows for precise control of the crystal nucleus growth rate by controlling the reducing agent. The purity of the glycerol is ≥99%; in the mixture containing potassium permanganate and glycerol, the ratio of potassium permanganate, water, and glycerol is 1–3 mmol: 40 mL: 2 mL; the preparation steps of the mixture containing potassium permanganate and glycerol include dissolving potassium permanganate in deionized water and sonicating for 15–25 minutes (e.g., 20 minutes), then adding glycerol and continuing sonication for 17–23 minutes. Adding 2 mL of glycerol is the experimentally optimized value; reducing the amount of glycerol decreases both the reducing power and viscosity, while increasing the amount of glycerol makes the reduction process more vigorous and faster, but may cause excessively rapid crystal nucleus formation, resulting in a large number of fine crystal nuclei. High viscosity strongly inhibits diffusion and growth.

[0025] According to an embodiment of the present invention, the mixing step includes ultrasonic treatment for 20 to 40 minutes, such as 30 minutes.

[0026] According to an embodiment of the present invention, the hydrothermal reaction temperature is 175–185°C, such as 180°C, and the hydrothermal reaction time is 9.5–10.5 hours, such as 10 hours. The hydrothermal temperature around 180°C is an experimentally optimized value because: 1. The hydroxyl group (-OH) in the glycerol molecule has reducing properties under high-temperature hydrothermal conditions (around 180°C); 2. When the hydrothermal temperature is below 175°C, the reducing power of glycerol is not strong enough, and the reduction reaction of potassium permanganate may be incomplete. Furthermore, 180°C is also a suitable temperature for the negative electrode to moderately reduce GO to rGO; 3. Temperatures above 185°C may lead to over-reduction, producing MnO impurities, or excessively crystallizable products with uncontrolled morphology.

[0027] Thirdly, the present invention provides a negative electrode sheet, comprising the manganese-based composite negative electrode material described above or the manganese-based composite negative electrode material prepared by the method described in any of the above.

[0028] Part Four, the present invention provides a method for preparing the negative electrode sheet, comprising the following steps: The manganese-based composite negative electrode material, conductive agent, and binder are mixed in a weakly acidic dispersant, and the resulting slurry is coated onto a substrate and dried to obtain the negative electrode sheet; the weakly acidic dispersant includes one of citric acid, tartaric acid, and malic acid.

[0029] The inventors discovered that using a weakly acidic dispersant is superior to other solvents. For example, citric acid contains one hydroxyl group and three carboxyl groups, making it a polydentate ligand with strong complexing ability. It also has moderate acidity and excellent water solubility. Citric acid can effectively buffer volume expansion, reduce the shedding of active materials, and maintain the integrity of the conductive network, thereby significantly extending the electrode cycle life.

[0030] According to embodiments of the present invention, the conductive agent includes one or more of conductive carbon black, carbon nanotubes (CNTs), and graphene; the binder includes one or more of carboxymethyl cellulose, polyacrylic acid, and polyimide; the mass ratio of the manganese-based composite negative electrode material, the conductive agent, and the binder is (7-8):(1-2):1, such as 7:2:1; the weakly acidic dispersant is added in the form of an aqueous solution with a concentration of 0.4-0.6 wt%, such as 0.5%; and the loading of the slurry is 1.1-1.3 mg / cm³. 2 For example, 1.2 mg / cm 2 .

[0031] Part 5: This invention provides a lithium-ion battery, comprising the manganese-based composite negative electrode material, or the manganese-based composite negative electrode material prepared by the method described in any of the above descriptions, or the negative electrode sheet, or the negative electrode sheet prepared by the method described in any of the above descriptions.

[0032] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0033] Unless otherwise specified, the methods used in the following embodiments are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0034] The graphene oxide used in the following examples was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., product code G476412.

[0035] Example 1 This embodiment provides a manganese-based composite anode material for lithium batteries, the anode material, and a method for preparing them.

[0036] The specific steps are as follows: 1.1 Preparation and treatment of the mixture 1 mmol of potassium permanganate was completely dissolved in 40 mL of deionized water and sonicated for 20 minutes. Then 2 mL of glycerol was added and sonication was continued for another 20 minutes. 15 mg of graphene oxide was dispersed in 35 mL of deionized water and sonicated for 20 minutes. The graphene oxide dispersion was added to a mixture of potassium permanganate and glycerol and sonicated for 30 minutes. 1.2 Hydrothermal Synthesis of Mn3O4-rGO Materials and Post-processing The mixture was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and sealed. It was heated at 180 °C for 10 hours, then cooled to room temperature. The dark brown product was removed, filtered with filter paper, washed several times with deionized water, and finally dried at 65 °C for 24 hours to obtain Mn3O4-rGO powder.

[0037] 1.3 Preparation of Mn3O4-rGO anode Mn3O4-rGO powder, conductive carbon black (Super P Carbon), and carboxymethyl cellulose (CMC) were mixed in a citric acid solution (0.5 wt%) at a weight ratio of 7:2:1. The viscosity of the slurry was controlled at 1500–4000 mPa•s. The resulting slurry was then coated onto a circular conductive steel substrate (with a loading of approximately 1.2 mg / cm²). 2 The anode was dried in a vacuum environment at 120°C for 12 hours to obtain Mn3O4-rGO anode.

[0038] Example 2 The difference from Example 1 is that the amount of potassium permanganate was adjusted to 2 mmol.

[0039] 1.1 Preparation and treatment of the mixture.

[0040] 2 mmol of potassium permanganate was completely dissolved in 40 mL of deionized water and sonicated for 20 minutes. Then 2 mL of glycerol was added and sonication was continued for another 20 minutes. 15 mg of graphene oxide was dispersed in 35 mL of deionized water and sonicated for 20 minutes. The graphene oxide dispersion was added to a mixture of potassium permanganate and glycerol and sonicated for 30 minutes. 1.2 Hydrothermal Synthesis of Mn3O4-rGO Materials and Post-processing The mixture was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and sealed. It was heated at 180 °C for 10 hours, then cooled to room temperature. The dark brown product was removed, filtered with filter paper, washed several times with deionized water, and finally dried at 65 °C for 24 hours to obtain Mn3O4-rGO powder.

[0041] 1.3 Preparation of Mn3O4-rGO anode Mn3O4-rGO powder, conductive carbon black (Super P Carbon), and carboxymethyl cellulose (CMC) were mixed in a citric acid solution (0.5 wt%) at a weight ratio of 7:2:1. The viscosity of the slurry was controlled at 1500–4000 mPa•s. The resulting slurry was then coated onto a circular conductive steel substrate (with a loading of approximately 1.2 mg / cm²). 2 The anode was dried in a vacuum environment at 120°C for 12 hours to obtain Mn3O4-rGO anode.

[0042] Example 3 The difference from Example 1 is that the amount of potassium permanganate was adjusted to 3 mmol.

[0043] 1.1 Preparation and treatment of the mixture 3 mmol of potassium permanganate was completely dissolved in 40 mL of deionized water and sonicated for 20 minutes. Then 2 mL of glycerol was added and sonication was continued for another 20 minutes. 15 mg of graphene oxide was dispersed in 35 mL of deionized water and sonicated for 20 minutes. The graphene oxide dispersion was added to a mixture of potassium permanganate and glycerol and sonicated for 30 minutes. 1.2 Hydrothermal Synthesis of Mn3O4-rGO Materials and Post-processing The mixture was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and sealed. It was heated at 180 °C for 10 hours, then cooled to room temperature. The dark brown product was removed, filtered with filter paper, washed several times with deionized water, and finally dried at 65 °C for 24 hours to obtain Mn3O4-rGO powder.

[0044] 1.3 Preparation of Mn3O4-rGO anode Mn3O4-rGO powder, conductive carbon black (Super P Carbon), and carboxymethyl cellulose (CMC) were mixed in a citric acid solution (0.5 wt%) at a weight ratio of 7:2:1. The viscosity of the slurry was controlled at 1500–4000 mPa•s. The resulting slurry was then coated onto a circular conductive steel substrate (with a loading of approximately 1.2 mg / cm²). 2 The anode was dried in a vacuum environment at 120°C for 12 hours to obtain Mn3O4-rGO anode.

[0045] Comparative Example 1 Mn3O4 was used as the negative electrode active material.

[0046] Comparative Example 2 The preparation method is the same as in Example 1, except that the amount of glycerol is adjusted to 1.5 mL.

[0047] Comparative Example 3 The preparation method is the same as in Example 1, except that the amount of glycerol is adjusted to 2.5 mL.

[0048] Comparative Example 4 The preparation method is the same as in Example 2, except that the amount of glycerol is adjusted to 1.5 mL.

[0049] Comparative Example 5 The preparation method is the same as in Example 2, except that the amount of glycerol is adjusted to 2.5 mL.

[0050] Comparative Example 6 The preparation method is the same as in Example 3, except that the amount of glycerol is adjusted to 1.5 mL.

[0051] Comparative Example 7 The preparation method is the same as in Example 3, except that the amount of glycerol is adjusted to 2.5 mL.

[0052] Characterization test cases The Mn3O4-rGO powders in the above examples and comparative examples were characterized and observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM should be performed at appropriate resolutions. Test data should be recorded and analyzed to ensure the successful preparation of Mn3O4-rGO.

[0053] The Mn3O4-rGO prepared in Examples 1-3 had high yields and the products were dark brown. Figures 1-3 The images shown are scanning electron microscope (SEM) images of Mn3O4-rGO from Examples 1-3, respectively. Figure 1-3 It can be seen that the powder product is characterized by uniform particles, octahedral structure, and complete rGO encapsulation.

[0054] The powder state and powder product characterization of Mn3O4-rGO prepared in Comparative Examples 2-7 are shown in Table 1.

[0055] Table 1. Comparison of the state and performance of manganese-based composite anode materials Mn3O4-rGO obtained in Comparative Examples 2-7

[0056] The difference between comparative examples 2-7 lies in the design of the potassium permanganate and glycerol addition amounts. Figures 1-3 As can be seen from Table 1, the morphology and state of the powder products in the comparative example are significantly different from those in Examples 1, 2, and 3 above. The reasons for the differences are: 1) Reducing the amount of glycerol decreases both the reducing power and viscosity during the reaction process; 2) Increasing the amount of glycerol makes the reduction process more intense and faster, but may cause the crystal nuclei to form too quickly, resulting in a large number of fine crystal nuclei and high viscosity strongly inhibiting diffusion and growth.

[0057] Performance Test Example 1 1. Preparation of lithium batteries The Mn3O4-rGO or Mn3O4 negative electrode prepared in the above embodiments was used as the working electrode, lithium foil as the counter electrode, Whatman glass fiber membrane as the battery separator, and 1M LiPF6 solution (prepared by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 ratio) as the electrolyte. Finally, CR 2032 coin cells were assembled in an argon-filled glove box.

[0058] 2. Electrical testing of lithium batteries The obtained coin cells were subjected to electrical tests using a Blue Electric Test Cabinet (CT3002A). The voltage range for cycle electrical performance (specific capacity) testing was 0.01V - 3V, and the test was conducted at 100 mA g. -1 The samples were tested at a constant current density, and the data were recorded and summarized. As shown in Figure 4, the initial specific capacity of Example 1 was similar to that of Examples 2 and 3 at 454.5 mAh / g, and significantly higher than that of Comparative Example 1 at 351.276 mAh / g. After 200 cycles, the capacity decreased to 449.3 mAh / g. The overall cycling trend was worse than that of Examples 2 and 3, but significantly better than that of Comparative Example 1, indicating that the Mn3O4-rGO composite material is beneficial for extending the cycle life of the battery. The initial specific capacity of Example 3 was similar to that of Examples 1 and 2 at 454.55 mAh / g, and significantly higher than that of Comparative Example 1. After 200 cycles, the capacity decreased to 451.8 mAh / g. The overall cycling trend was better than that of Example 1 but worse than that of Example 2, and significantly better than that of Comparative Example 1.

[0059] Table 2 shows the performance comparison of Mn3O4-rGO prepared in Comparative Examples 2-7 after 200 cycles.

[0060] Table 2. Performance Comparison of Manganese-based Composite Anode Materials Mn3O4-rGO Obtained in Comparative Examples 2-7

[0061] As can be seen from Table 2, the performance of Comparative Examples 2-7 after 200 cycles is also inferior to that of Examples 1, 2, and 3, which is consistent with the changes in their powder state and powder product characterization results.

[0062] Performance Test Example 2 1. Preparation of lithium batteries Similar to performance test example 1, a coin cell was prepared using the Mn3O4-rGO negative electrode sheet from example 2.

[0063] 2. Electrical testing of lithium batteries Electrochemical impedance spectroscopy (EIS) tests were performed on the obtained cells and Comparative Example 1 (a coin cell with Mn3O4 as the negative electrode) using an electrochemical workstation (Chenhua CHI660e). The electrical properties of the obtained coin cells were tested using a Blue Electric test cabinet (CT3002A). The EIS spectra were obtained using the electrochemical workstation, with an AC voltage amplitude of 10 mV and a frequency range of 100 kHz – 100 mHz. The data were recorded and fitted to obtain the Nyquist plot. Figure 5 The impedance Nyquist plots for Example 2 and Comparative Example 1 show a single semicircular curve in the high-frequency region and a gently sloping straight line in the low-frequency range, corresponding to charge transfer resistance (Rct) and lithium-ion solid-state diffusion (Zw), respectively. The radius and corresponding values ​​in the straight-line region of Example 2 are significantly lower than those of Comparative Example 1, indicating that its Rct value is lower than the control sample. This also shows that the Mn3O4-rGO composite structure can promote rapid charge transfer compared to the pure Mn3O4 structure. The cycle electrical performance (specific capacity) was obtained using a blue electric test cabinet, with a test voltage range of 0.01V - 3V, at 100 mAg. -1 The samples were tested at a constant current density, and the data were recorded and summarized. As shown in Figures 4-5, the initial specific capacity of Example 2 was similar to that of Examples 1 and 3 at 454.1 mAh / g, significantly higher than that of Comparative Example 1. After 200 cycles, it decreased to 452.78 mAh / g. The overall cycling trend was better than that of Examples 1 and 3, and significantly better than that of Comparative Example 1. The cycling performance at different current densities was obtained using a blue battery test cabinet with a test voltage range of 0.01V - 3V. The results are shown in Table 3. By conducting constant current cycling tests at different current rates, the rate performance of the electrode was verified. Compared with the pure Mn3O4 electrode, the Mn3O4-rGO composite electrode showed significantly enhanced rate performance, indicating that the synergistic effect of the Mn3O4-rGO composite material is beneficial to the rate performance of the battery.

[0064] Table 3 shows the electrical performance of the coin cell of the present invention with Example 2 as the negative electrode and Comparative Example 1 (a coin cell prepared with pure Mn3O4 as the working electrode according to the same scheme as the Example) after 110 cycles at different current densities (rates).

[0065] Table 3. Performance Comparison of Examples and Comparative Example 1

[0066] In summary, the comparison results show that the optimal ratio of manganese source to glycerol in this invention is 1–3 mmol: 2 mL. Excessive or insufficient glycerol usage negatively impacts cycle performance. A ratio of 2 mmol: 2 mL yields the best cycle life and rate performance. This is because the addition of glycerol and adjustment of the manganese source to glycerol ratio in this invention provides a conductive three-dimensional network structure for Mn3O4 within the graphene matrix. The Mn3O4 nano-octahedrons prevent the graphene layers from re-stacking, and the graphene-encapsulated Mn3O4 nanostructure reduces volume expansion during charge and discharge, thereby extending cycle life. Furthermore, the high porosity and low diffusion resistance of the graphene matrix itself, along with the three-dimensional interconnection with Mn3O4, enhance electrical conductivity and ionic conductivity, thus improving rate performance.

[0067] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including modifications made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A manganese-based composite negative electrode material, characterized in that, The manganese-based composite negative electrode material is a composite of trimanganese tetraoxide and reduced graphene oxide. 2.The manganese-based composite negative material according to claim 1, characterized in that: The trimanganese tetraoxide has an octahedral structure.

3. The method of producing a manganese-based composite negative electrode material according to any one of claims 1 to 2, characterized by, The method comprises the following steps: The manganese-based composite negative electrode material is obtained by mixing a dispersion liquid containing graphene oxide with a mixed solution containing a manganese source and glycerol through a hydrothermal reaction.

4. The method for preparing a manganese-based composite negative material according to claim 3, characterized in that: In the dispersion liquid containing graphene oxide, the ratio of graphene oxide to water is 15 mg: 30-40 mL; And / or, the preparation step of the dispersion liquid containing graphene oxide comprises ultrasonic treatment of graphene oxide and water for 15-25 minutes.

5. The method for preparing the manganese-based composite anode material according to claim 3, characterized in that: The manganese source is a solid powder with a purity of ≥96%; And / or, the manganese source comprises one or more of potassium permanganate, manganese sulfate, and manganese chloride; And / or, the glycerol has a purity of ≥99%; And / or, in the mixed solution containing the manganese source and glycerol, the ratio of the manganese source to glycerol is 1-3 mmol: 2 mL; And / or, the mixed solution containing the manganese source and glycerol further contains water, and the ratio of the manganese source to water is 1-3 mmol: 40 mL; And / or, the preparation step of the mixed solution containing the manganese source and glycerol comprises dissolving the manganese source in deionized water and ultrasonic treatment for 15-25 minutes, followed by adding glycerol and continuing ultrasonic treatment for 17-23 minutes.

6. The method for preparing the manganese-based composite anode material according to claim 3, characterized in that: The mixing step comprises ultrasonic treatment for 20-40 minutes; And / or, the temperature of the hydrothermal reaction is 175-185°C; And / or, the time of the hydrothermal reaction is 9.5-10.5 hours.

7. A negative electrode sheet characterized by comprising: The manganese-based composite negative electrode material prepared by the method of any one of claims 3-6.

8. The method of producing the negative electrode sheet according to claim 7, characterized by The method comprises the following steps: The manganese-based composite negative electrode material, a conductive agent, and a binder are mixed in a weakly acidic dispersant, and the obtained slurry is coated on a substrate to obtain the negative electrode sheet through drying; the weakly acidic dispersant comprises any one of citric acid, tartaric acid, and malic acid.

9. The method according to claim 8, wherein: The conductive agent comprises one or more of conductive carbon black, carbon nanotubes, and graphene; And / or, the binder comprises one or more of carboxymethyl cellulose, polyacrylic acid, and polyimide; And / or, the mass ratio of the manganese-based composite negative electrode material, the conductive agent, and the binder is (7-8):(1-2):1; And / or, the weakly acidic dispersant is added in the form of an aqueous solution with a concentration of 0.4-0.6 wt%; and / or the slurry has a loading of 1.1 to 1.3 mg / cm 2 .

10. A lithium-ion battery, characterized by, The manganese-based composite negative electrode material of any one of claims 1-2, or the manganese-based composite negative electrode material prepared by the method of any one of claims 3-6, or the negative electrode sheet of claim 7, or the negative electrode sheet prepared by the method of any one of claims 8-9.

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