A cathode composite material applied to a lithium-indigo blue energy storage battery and a preparation method and application thereof

Abstract

The application belongs to the technical field of energy storage batteries, and particularly relates to a cathode composite material applied to a lithium-indigo energy storage battery and a preparation method and application thereof. The preparation method is that biomass carbon source, nitrogen source, pore-forming agent and iron-cobalt salt are mixed, a porous carbon material is constructed through ball milling, drying and high-temperature calcination, and a cathode active substance is compounded with the porous carbon material through a high-temperature melting method. The Fe-Co nano-alloy catalyst is integrated into the porous biomass carbon skeleton, the problems of poor conductivity of the organic electrode material, slow reaction kinetics and dissolution of the active substance are solved, the nano-alloy catalyst and the biomass carbon are used to jointly construct an efficient conductive network, the electron transmission is accelerated, the indigo-based compound is loaded through the high-temperature melting method, the dissolution of the indigo-based compound is inhibited, and the cycle stability of the battery is improved.

Description

Technical Field

[0001] This invention belongs to the field of energy storage battery technology, specifically relating to a cathode composite material for lithium-indigo energy storage batteries, its preparation method, and its application. Background Technology

[0002] Currently, the lithium-ion battery market is large and continues to grow, but its mainstream transition metal-based inorganic cathode materials face problems such as high cost, environmental pollution, and near-limited theoretical specific capacity, making it difficult to meet future market demands for high-performance batteries. Therefore, organic electrode materials composed of abundant elements such as carbon, hydrogen, and oxygen have become a highly promising alternative due to their unique advantages such as lightness, environmental friendliness, low cost, and structural diversity. However, organic materials generally suffer from two major challenges: poor electronic conductivity and easy solubility in electrolytes, leading to shuttle effects and resulting in unstable battery performance.

[0003] In the field of energy storage technology, lithium-ion batteries using organic carbonyl compounds such as indigo as positive electrode active materials have attracted widespread attention due to their advantages such as low cost, environmental friendliness, and high structural designability. These batteries achieve energy storage and release through the reversible redox reaction of the carbonyl group (C=O) in the indigo molecule. However, existing lithium-indigo batteries still face multiple technical bottlenecks, severely restricting their commercial application.

[0004] In terms of cathode materials, indigo, as a small organic molecule, has extremely poor electronic conductivity, leading to sluggish electrode reaction kinetics. Furthermore, indigo and its lithiation products are readily soluble in organic electrolytes. The dissolved active material migrates and crosses the separator, triggering a "shuttle effect." This not only causes continuous loss of active material from the cathode but also corrodes the surface of the lithium metal anode, resulting in rapid capacity decay and shortened cycle life. While existing technologies attempt to combine indigo with conductive matrices such as porous carbon to alleviate the dissolution problem and improve conductivity through physical confinement, these non-catalytically active carbon supports have limited effect on accelerating the redox conversion kinetics of indigo, especially under high-rate charge / discharge and high active material loading conditions, where the performance improvement is not ideal.

[0005] Therefore, developing a novel composite cathode material that can provide both a highly conductive network and a porous structure, and can also catalyze the conversion of active materials, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the common problems of poor electronic conductivity, lithium dendrites, disordered migration of reaction intermediates, slow redox reaction kinetics, and significant shuttle effects in organic materials, this invention proposes a method for preparing a cathode composite material based on nitrogen-doped iron-cobalt nanoalloy porous biomass conductive carbon with high-temperature molten loading of active material for energy storage batteries composed of the organic dye indigo and lithium. This invention enhances the electron transport rate by constructing an effective conductive network; simultaneously, the introduction of an iron-cobalt nanoalloy catalyst further improves the redox reaction kinetics of indigo. This strategy of combining indigo with conductive carbon materials and loading a catalyst provides an effective way to improve the conductivity and reaction kinetics of organic cathode materials and solve their solubility problems. This design significantly improves the specific capacity and cycle stability of the battery, thereby promoting the application and development of organic cathode materials in the field of high-performance batteries.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] This invention provides a method for preparing a cathode composite material for lithium-indigo energy storage batteries, comprising the following steps: S1: The biomass carbon source, nitrogen source, pore-forming agent, iron source and cobalt source are mixed and loaded into a ball mill, ball-milled in ethanol, and dried to obtain a precursor containing Fe and Co nano-ions; S2: The precursor obtained in step S1 is calcined, washed, and dried in an inert gas atmosphere to obtain nitrogen-doped iron-cobalt nanoalloy porous biomass conductive carbon. S3: The nitrogen-doped iron-cobalt nanoalloy porous biomass conductive carbon obtained in step S2 is mixed with the cathode active material, and then the cathode composite material is obtained by high-temperature melting and calcination under an inert gas atmosphere.

[0009] In the above technical solution, further, in step S1, the biomass carbon source includes one of guar gum, creatine, coconut shell, sawdust, rice husk, and corn cob; The nitrogen source includes one of dicyandiamide, urea, cyanide, amine compounds, amino acids, and nitrogen compounds; The pore-forming agent includes one of sodium chloride, potassium chloride, calcium chloride, sodium hydroxide, zinc chloride, phosphoric acid, sulfuric acid, calcium hydroxide, sodium carbonate, and silica gel. The iron source includes one of ferric nitrate, ferric oxide, ferric chloride, ferric sulfide, and potassium ferricyanide; The cobalt source includes one of cobalt nitrate, cobalt oxide, cobalt chloride, cobalt sulfide, and cobalt salts.

[0010] In the above technical solution, further, in step S1, the mass ratio of iron in the biomass carbon source, nitrogen source, pore-forming agent, and iron source to cobalt in the cobalt source is 4.0:4.0:5.0:0.2:0.211.

[0011] In the above technical solution, further, in step S1, the ball milling time is 8-18 hours.

[0012] In the above technical solution, further, in step S1, the drying temperature is 60-80℃ and the time is 20-24h.

[0013] In the above technical solution, further, in step S2, the inert gas is one or both of nitrogen and argon; The calcination temperature is 800-990℃, the holding time is 1-3h, and the heating rate is 3-6℃ / min.

[0014] In the above technical solution, further, in step S3, the inert gas is one or both of nitrogen and argon; The parameters for the high-temperature melting and calcination method are as follows: calcination temperature is 385-405℃, holding time is 1-3h, and heating rate is 3-6℃ / min.

[0015] In the above technical solution, further, in step S3, the cathode active material is an indigo-based compound.

[0016] In another aspect, the present invention provides a cathode composite material prepared by the above-mentioned preparation method. The cathode composite material is composed of nitrogen-doped iron-cobalt nanoalloy porous biomass conductive carbon and cathode active material. The nitrogen-doped iron-cobalt nanoalloy porous biomass conductive carbon has a core-shell structure, with the core material being iron-cobalt nanoalloy and the shell material being nitrogen-doped porous biomass conductive carbon.

[0017] The present invention also provides an application of the above-mentioned cathode composite material in a lithium-indigo energy storage battery.

[0018] In the above technical solution, the battery is further described as a button cell, pouch cell, cylindrical cell, or solid-state structure.

[0019] The beneficial effects of this invention are as follows: 1. In the preparation method of the present invention, during the carbonization process, the nitrogen source and the pore-forming agent jointly regulate the formation of a uniform porous structure. At the same time, iron and cobalt generate carbon-encapsulated FeCo alloy catalysts and are uniformly dispersed in the material. This porous carbon material has a high specific surface area, abundant micropores and mesopores, as well as the synergistic effect of FeCo and N, which helps to improve the electrochemical performance of the material and its ability to anchor active substances.

[0020] 2. In this invention, the cathode active material is encapsulated in the three-dimensional pores and channels of N-MPC@FeCo carbon material through melt diffusion, constructing a highly efficient conductive network. The porous carbon not only improves the electronic conductivity of indigo-based compounds, but its porous structure can also effectively stabilize and restrict indigo leuco within the carbon skeleton through physical adsorption, thereby inhibiting the dissolution of the cathode active material in the electrolyte and the "shuttle effect".

[0021] 3. This invention significantly improves the conductivity and stability of indigo through porous carbon doping, thereby significantly improving the cycle life and rate performance of the battery. This structural regulation strategy provides an effective way for the application of organic cathode materials in the field of high-performance batteries. Attached Figure Description

[0022] The invention will be further illustrated with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the invention. For those skilled in the art, other drawings can be obtained based on the following drawings without any creative effort.

[0023] Figure 1 SEM images of N-MPC@FeCo, NC@FeCo, MPC@FeCo, and N-MPC are shown. a is N-MPC@FeCo, b is NC@FeCo, c is MPC@FeCo, and d is N-MPC. Figure 2 XRD pattern of N-MPC@FeCo; Figure 3 TEM image of N-MPC@FeCo; Figure 4 High-magnification images of the N-MPC@FeCo region, showing the corresponding diffraction spots and labeled crystal plane types; Figure 5 High-resolution XPS spectra of C1s for N-MPC@FeCo; Figure 6 The N 1s high-resolution XPS spectrum of N-MPC@FeCo; Figure 7 High-resolution XPS spectra of Fe 2p in N-MPC@FeCo; Figure 8 High-resolution XPS spectra of Co 2p for N-MPC@FeCo; Figure 9 These are before-and-after photos showing the adsorption of indigo in liquid electrolytes. Figure 10The N2 adsorption-desorption isotherms and pore size distribution curves of the samples are shown in Figure 1. Figure 2 shows the N2 adsorption-desorption isotherms of N-MPC@FeCo, MPC@FeCo, NC@FeCo and N-MPC. Figure 3 shows the N2 adsorption-desorption isotherms and pore size distribution curves of N-MPC@FeCo. Figure 4 shows the pore size distribution curves of N-MPC@FeCo, MPC@FeCo, NC@FeCo, N-MPC and N-MPC@FeCo / Indigo. Figure 11 Raman spectra of N-MPC@FeCo, MPC@FeCo, NC@FeCo and N-MPC; Figure 12 N2 adsorption-desorption isotherms for N-MPC@FeCo and N-MPC@FeCo / Indigo; Figure 13 SEM images of N-MPC@FeCo; Figure 14 The images are SEM images and corresponding EDX images of N-MPC@FeCo / Indigo. a is the SEM image, b is a magnified view of a, c is the EDX image of C, d is the EDX image of Fe, e is the EDX image of Co, f is the EDX image of O, and g is the EDX image of N. Figure 15 The CV curves and lithium-ion diffusion coefficient plots are shown for N-MPC@FeCo / Indigo, NC@FeCo / Indigo, MPC@FeCo / Indigo and N-MPC / Indigo. a is the CV curve and b is the lithium-ion diffusion coefficient plot. Figure 16 The AC impedance curves of N-MPC@FeCo / Indigo, NC@FeCo / Indigo, MPC@FeCo / Indigo and N-MPC / Indigo at 0.2 C are shown. Figure 17 Rate performance from 0.2 C to 3.0 C for N-MPC@FeCo / Indigo, NC@FeCo / Indigo, MPC@FeCo / Indigo, and N-MPC / Indigo; Figure 18 The constant current charge-discharge cycle performance of Indigo at 0.2 C is shown in Figure a, where a represents the constant current charge-discharge cycle performance at 0.2 C, and b represents the constant current charge-discharge cycle curve. Figure 19 Infrared-visible spectra of the Indigo redox process; Figure 20The constant current charge-discharge cycle performance of N-MPC@FeCo / Indigo, NC@FeCo / Indigo, MPC@FeCo / Indigo and N-MPC / Indigo electrodes at 0.2 C is presented. Figure 21 The constant current charge-discharge cycle performance of N-MPC@FeCo / Indigo at 0.5 C; Figure 22 The constant current charge-discharge cycle performance of the N-MPC@FeCo / Indigo Carmine electrode at 0.2 C is shown. Detailed Implementation

[0024] To better illustrate the objectives, technical solutions, and advantages of this invention, the following embodiments are provided. Obviously, the following embodiments are only a part of the embodiments of this invention, and not all of them; it should be understood that the embodiments of this invention are only used to illustrate the technical effects of this invention, and not to limit the scope of protection of this invention.

[0025] All raw materials used in the examples are commercially available; unless otherwise specified, the reagents, methods and equipment used in this invention are conventional reagents, methods and equipment in this technical field.

[0026] Example 1 A method for preparing a nitrogen-doped iron-cobalt nanoalloy porous biomass conductive carbon-supported active material cathode composite material includes the following steps: S1: 4g of guar gum, 4g of dicyandiamide, Fe(NO3)3·9H2O containing 0.2g of iron, Co(NO3)2·4H2O containing 0.211g of cobalt, and 5g of NaCl were placed in a ball mill and ball-milled in ethanol (the weight ratio of ethanol to carbon source was 2-5:1) for 12 hours. Then the mixture was dried in an oven for 23 hours to obtain a precursor containing FeCo nano-alloys. S2: The precursor is placed in a ceramic boat in a tube furnace and heated in argon gas at 950℃ for 5 minutes. -1 The heating rate was calcined for 2 hours to produce black powder. The collected black powder was washed with deionized water and filtered until NaCl was completely washed away. The filtrate was tested with silver nitrate solution until no white precipitate was formed. The filtrate was dried overnight at 70°C in a vacuum oven to obtain nitrogen-doped iron-cobalt nanoalloy porous biomass carbon, denoted as N-MPC@FeCo. S3: The nitrogen-doped iron-cobalt nanoalloy porous biomass carbon obtained in step S2 and the active material indigo are ball-milled once at a mass ratio of 1:1 to ensure thorough mixing. The mixture is then placed in a ceramic boat in the middle of a tube furnace and heated to 395°C at a heating rate of 3°C / min under an Ar inert atmosphere. The mixture is held at this temperature for 2 hours to allow for high-temperature melting and diffusion, resulting in a nitrogen-doped iron-cobalt nanoalloy porous biomass conductive carbon-supported active material cathode composite material, denoted as N-MPC@FeCo / Indigo.

[0027] Example 2 A method for preparing a nitrogen-doped iron-cobalt nanoalloy porous biomass conductive carbon-supported active material cathode composite material includes the following steps: S1: 4g of guar gum, 4g of dicyandiamide, Fe(NO3)3·9H2O containing 0.2g of iron, Co(NO3)2·4H2O containing 0.211g of cobalt, and 5g of NaCl were placed in a ball mill and ball-milled in ethanol (the weight ratio of ethanol to carbon source was 2-5:1) for 12 hours. Then the mixture was dried in an oven for 23 hours to obtain a precursor containing FeCo nano-alloys. S2: The precursor is placed in a ceramic boat in a tube furnace and heated in argon gas at 950℃ for 5 minutes. -1 The heating rate was calcined for 2 hours to produce black powder. The collected black powder was washed with deionized water and filtered until NaCl was completely washed away. The filtrate was tested with silver nitrate solution until no white precipitate was formed. The filtrate was dried overnight at 70°C in a vacuum oven to obtain nitrogen-doped iron-cobalt nanoalloy porous biomass carbon. S3: The nitrogen-doped iron-cobalt nanoalloy porous biomass carbon obtained in step S2 and the active material sodium indigo disulfonate (Indigo Carmine) are ball-milled once at a mass ratio of 1:1 to ensure thorough mixing. The mixture is then placed in a ceramic boat in the middle of a tube furnace and heated to 395°C at a heating rate of 3°C / min under an Ar inert atmosphere. The mixture is held at this temperature for 2 hours to perform high-temperature melting and diffusion, resulting in a nitrogen-doped iron-cobalt nanoalloy porous biomass conductive carbon-supported active material cathode composite material, denoted as N-MPC@FeCo / Indigo Carmine.

[0028] Comparative Example 1 A method for preparing a porous biomass carbon-supported active material cathode composite material of iron-cobalt nanoalloy includes the following steps: S1: 4g of guar gum, Fe(NO3)3·9H2O containing 0.2g of iron, Co(NO3)2·4H2O containing 0.211g of cobalt, and 5g of NaCl were placed in a ball mill and ball-milled in ethanol (the weight ratio of ethanol to carbon source was 2-5:1) for 12 hours. Then the mixture was dried in an oven for 23 hours to obtain a precursor containing FeCo nano-alloys. S2: The precursor is placed in a ceramic boat in a tube furnace and heated in argon gas at 950℃ for 5 minutes. -1 The mixture was calcined at a heating rate of 2 h to produce a black powder. The collected black powder was washed with deionized water and filtered until NaCl was completely removed. The filtrate was tested with silver nitrate solution until no white precipitate was formed. The filtrate was then dried overnight at 70 °C in a vacuum oven. The resulting solid substance was denoted as MPC@FeCo. S3: The solid material obtained in step S2 and the active material indigo are ball-milled once at a mass ratio of 1:1 to ensure thorough mixing. The mixture is then placed in a ceramic boat in the middle of a tube furnace. Under an Ar inert atmosphere, the temperature is increased to 395°C at a heating rate of 3°C / min and held for 2 hours to perform high-temperature melting and diffusion, resulting in a porous biomass carbon-supported active material cathode composite material of iron-cobalt nanoalloy, denoted as MPC@FeCo / Indigo.

[0029] Comparative Example 2 A method for preparing a nitrogen-doped iron-cobalt nanoalloy biomass carbon-supported active material cathode composite material includes the following steps: S1: 4g of guar gum, 4g of dicyandiamide, Fe(NO3)3·9H2O containing 0.2g of iron, and Co(NO3)2·4H2O containing 0.211g of cobalt were placed in a ball mill and ball milled in ethanol (the weight ratio of ethanol to carbon source was 2-5:1) for 12 hours. Then the mixture was dried in an oven for 23 hours to obtain a precursor containing FeCo nano-alloys. S2: The precursor is placed in a ceramic boat in a tube furnace and heated in argon gas at 950℃ for 5 minutes. -1 The product was calcined at a heating rate of 2 h to produce a black powder, which was then dried overnight at 70 °C in a vacuum oven. The resulting solid was denoted as NC@FeCo. S3: The solid material obtained in step S2 and the active material indigo are ball-milled once at a mass ratio of 1:1 to ensure thorough mixing. The mixture is then placed in a ceramic boat in the middle of a tube furnace and heated to 395°C at a heating rate of 3°C / min under an Ar inert atmosphere. The mixture is held at this temperature for 2 hours to allow for high-temperature melting and diffusion, resulting in a porous biomass carbon-supported active material cathode composite material of iron-cobalt nanoalloy, denoted as NC@FeCo / Indigo.

[0030] Comparative Example 3 A method for preparing a nitrogen-doped porous biomass carbon-supported active material cathode composite material includes the following steps: S1: Place 4g of guar gum, 4g of dicyandiamide and 5g of NaCl into a ball mill and ball mill in ethanol (the weight ratio of ethanol to carbon source is 2-5:1) for 12 hours. Then place it in an oven to dry for 23 hours to obtain the precursor. S2: The precursor is placed in a ceramic boat in a tube furnace and heated in argon gas at 950℃ for 5 minutes. -1 The mixture was calcined at a heating rate of 2 h to produce a black powder. The collected black powder was washed with deionized water and filtered until NaCl was completely washed away. The filtrate was tested with silver nitrate solution until no white precipitate was formed. The filtrate was then dried overnight at 70 °C in a vacuum oven. The resulting solid substance was denoted as N-MPC. S3: The solid material obtained in step S2 and the active material indigo are ball-milled once at a mass ratio of 1:1 to ensure thorough mixing. The mixture is then placed in a ceramic boat in the middle of a tube furnace and heated to 395°C at a heating rate of 3°C / min under an Ar inert atmosphere. The mixture is held at this temperature for 2 hours to allow for high-temperature melting and diffusion, resulting in a nitrogen-doped porous biomass carbon-supported active material cathode composite material, denoted as N-MPC / Indigo.

[0031] Figure 1 Scanning electron microscopy (SEM) images of the prepared samples were used to reveal the morphology and microstructure of the composite material. As shown in Figure a, the complex porous structure with numerous irregular pores and voids indicates that the material has a high specific surface area, making it suitable for applications such as catalysis and adsorption. A multi-scale pore structure was observed, revealing a 3D network interconnection distribution within the porous layered structure. Furthermore, in the absence of NaCl as a spatial support, Figure 1 b shows that its surface is relatively dense and has no obvious pores. Figure 1 c represents the MPC@FeCo sample, which exhibits a non-uniform and unconnected disordered structure. The formation of this disordered structure is due to the lack of DICY etching on the material surface. Figure 1 d represents the N-MPC sample. For materials without the addition of Fe(NO3)3·9H2O and Co(NO3)2·4H2O, the N-MPC sample exhibits a morphology similar to N-MPC@FeCo, indicating that the addition of FeCo does not disrupt the original structure of N-MPC@FeCo. Therefore, the combined regulation of DICY and NaCl results in N-MPC@FeCo possessing a more abundant and uniform porous structure with micropores, mesopores, and self-interconnected networks.

[0032] Figure 2-4For the physical structure characterization of N-MPC@FeCo samples, X-ray diffraction (Powder XRD) was used to study the phase formation and purity of different samples. Figure 2 Exhibiting typical characteristics of amorphous carbon, the N-MPC@FeCo composite material, after high-temperature calcination, exhibits three typical peaks at 47.8°, 66.3°, and 85.7°, corresponding to the (110), (200), and (211) planes of the body-centered cubic (bcc) FeCo alloy (JCPDS# 049-156), respectively. XRD results confirmed that the precursor pyrolysis formed crystalline FeCo alloy nanoparticles and a porous carbon shell, consistent with TEM results and subsequent transmission electron microscopy results.

[0033] To observe more details of the microstructure of the prepared catalyst, we further analyzed it using transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HR-TEM). Figure 3 The morphology of N-doped porous carbon-encapsulated nanoalloy particles is shown, and TEM images demonstrate the successful synthesis of the nanoalloy catalyst. Consistently, selected area electron diffraction (SAED) patterns are observed. Figure 4 The diffraction patterns of the lattice planes belonging to these species were displayed. The abundant oxygen-containing functional groups (such as hydroxyl groups) in the guar gum (GG) molecular chain can generate Fe... 3+ Co 2+ Ions undergo coordination chelation, achieving atomic-level uniform dispersion of metal ions in the precursor. Other carbon sources with similar structures mentioned in this paper have been confirmed to have the same mechanism of action. During high-temperature carbonization, the in-situ formed biomass carbon framework exerts a significant spatial confinement effect on the metal nanoparticles, effectively inhibiting the excessive growth and agglomeration of FeCo alloy grains. Furthermore, it promotes the tight coating of the generated nitrogen-doped porous carbon layer on the surface of the nano-alloy, ultimately forming a core-shell structured N-MPC@FeCo composite material. The above results confirm the existence of N-MPC@FeCo and nitrogen doping. XRD patterns confirm the presence of the FeCo alloy, and its interplanar spacing conforms to the characteristics of FeCo alloys. TEM and HRTEM images show that the material has a uniform porous structure, with FeCo alloy particles uniformly dispersed and without agglomeration.

[0034] Figure 5-8 XPS spectra of N-MPC@FeCo samples, from Figure 5In the C1s spectrum, signals of CC and CN can be observed at 284.8 eV, and another prominent peak appears near 286.5 eV, corresponding to CO bonds. These results indicate that the material surface is rich in carbon and has certain oxidation properties, suggesting that it may have active sites for redox reactions during catalysis. Figure 6 The N1s spectrum in the sample showed three main peaks at 398.4 eV (metal-N), 400.2 eV (pyrrole-N), and 401.2 eV (nitrogen heterocyclic-N). These signals indicate that nitrogen exists in different chemical environments within the carbon material, and the coexistence of pyrrole-N and metal-N provides more catalytic sites, which is beneficial for enhancing the catalytic activity of the material. Figure 7 The Fe2p spectrum shows that Fe 3+ Fe 2+ and Fe 0 Multiple peaks are located at 711.2 eV (Fe). 2+ ), 723.0 eV (Fe 3+ ) and 709.6 eV (Fe 0 At the positions indicated, these signals suggest that iron exists in both oxidized and metallic states. The spin splitting (2p1 / 2 and 2p3 / 2) peaks in the Fe2p spectrum further confirm the different chemical states of Fe, which is crucial for enhancing the catalytic and adsorption performance of materials. Figure 8 The Co2p spectrum shows Co 3+ and Co 2+ The characteristic peaks are located at 780.5 eV (Co). 3+ ) and 783.7 eV (Co 2+ Furthermore, the satellite peaks in the Co2p spectrum also indicate different oxidation states of cobalt, which may be related to the catalytic performance of the material and the high efficiency of the catalytic reaction.

[0035] Figure 9 The color change in the middle bottle indicates that this carbon material has a strong adsorption effect on indigo in the electrolyte. This can effectively reduce the dissolution of active materials in the electrolyte. Adsorption experiments can further verify the anchoring ability of FeCo and nitrogen species carbon materials in lithium indigo batteries.

[0036] To investigate the combined effects of NaCl and DICY on the pore size and pore distribution of composite materials, adsorption-desorption experiments were conducted on these four materials under a N2 atmosphere at 77 K. Figure 10As shown in a and b, N-MPC@FeCo, MPC@FeCo, NC@FeCo, and N-MPC exhibit Type IV isotherms according to IUPAC classification and H3 hysteresis with capillary condensation. The presence of mesopores and macropores is confirmed in the medium- and high-pressure regions, consistent with SEM observations. The BET specific surface areas of N-MPC@FeCo, MPC@FeCo, NC@FeCo, and N-MPC are 479.04, 651.18, 32.44, and 138.55 m², respectively. 3 g -1 .

[0037] Figure 10 c shows the pore size distribution of N-MPC@FeCo, MPC@FeCo, NC@FeCo, and N-MPC, with pore diameters of 4.76–1.77, 7.37–2.13, 3.71–1.29, and 8.05–1.75 μm, respectively. 3 g -1 N-MPC@FeCo exhibits high pore volume and multi-scale pores. The reasons are as follows: (1) The ammonia gas generated during the pyrolysis of DICY etches the surface structure of the carbon matrix, thereby increasing the number of micropores and mesopores. (2) In the temporary space constructed by NaCl as a hard template, the material forms a uniform and controllable multi-scale pore and layered structure. However, some pores of N-MPC@FeCo are blocked by N and FeCo, resulting in a relatively small specific surface area. Figure 10 c also shows the pore size distribution of N-MPC@FeCo and N-MPC@FeCo / Indigo. The N-MPC@FeCo composite exhibits significant mesopore and macropore characteristics, with the pore size distribution concentrated in the range of approximately 4-10 nm. This pore size distribution indicates that the material is suitable for the adsorption of indigo, especially when indigo molecules are relatively large, enabling more efficient molecular-level adsorption and storage. In contrast, N-MPC@FeCo / Indigo has more uniform pores and smaller pore sizes, which further optimizes the diffusion and adsorption process of indigo molecules within the smaller pores.

[0038] Figure 11 The in-situ Raman spectra of N-MPC@FeCo, MPC@FeCo, NC@FeCo, and N-MPC are shown. Raman spectroscopy is used to test the defect features and active sites of materials. The absence of D and G bands reflects the near absence of carbon-based material formation during the high-temperature phosphating process. Conversely, disordered carbon (D band) and graphitic carbon (G band) in N-MPC@FeCo, MPC@FeCo, NC@FeCo, and N-MPC are observed at 1350 cm⁻¹. -1 and 1600cm -1The intensity ratio of the D band to the G band of the four materials was observed to be (I) D / I G The values ​​are 1.14, 1.11, 1.10, and 0.59, respectively. We can find that N-MPC@FeCo has the highest Ig. D / I G The ratio means that the material contains more defects. The synthesis of FeCo exposes more active sites for N-MPC@FeCo, thereby increasing the kinetics of the indigo redox reaction.

[0039] Adsorption-desorption experiments were conducted on N-MPC@FeCo loaded with indigo. Figure 12 According to calculations by BJH and Horvath-Kawazoe, the pores of N-MPC@FeCo are almost entirely filled with indigo-based compounds. Furthermore, the specific surface area decreases significantly, further indicating that indigo has successfully infiltrated the porous structure of N-MPC@FeCo.

[0040] Figure 13 , 14 Energy-dispersive X-ray (EDX) spectroscopy of N-MPC@FeCo also confirmed the presence of C, N, O, Fe, and Co. This is consistent with previous XRD, BET, and Raman results. All these results indicate that indigo is uniformly dispersed in the carbon material. The self-made nitrogen-doped carbon material possesses excellent specific surface area, a porous and interconnected structure, providing more catalytic active sites, faster electron transfer rates, stronger physical adsorption, and effective prevention of active material loss. This results in a good effect on inhibiting the dissolution of active materials in the electrolyte and promoting the conductivity of the active materials.

[0041] Figure 15 The CV curves and lithium-ion diffusion rate test results for lithium batteries assembled using the cathode materials of Examples 1-3 are presented. The CV curves for N-MPC@FeCo / Indigo are obtained at a rate of 0.1 mV / s over a voltage range of 1.5 to 3.0 V. -1 The scan rate obtained ( Figure 15 a). Near 1.95 V, we observed a reduction peak for indigo, indicating that indigo was reduced to Leuco-indigo. N-MPC@FeCo / Indigo showed an oxidation peak near 2.65 V, attributed to the conversion of indigo. Notably, the peak positions and peak areas of N-MPC@FeCo / Indigo essentially overlapped after three cycles. In contrast, the CV curves of the other three cathodes all showed significant shifts ( Figure 15a) This result confirms that N-MPC@FeCo / Indigo possesses low electrochemical polarity, high reversibility, and excellent stability. N-MPC@FeCo / Indigo exhibits high peak area and intensity, as well as sharp peak shape. These results indicate that, through the synergistic effect of FeCo and N species, N-MPC@FeCo / Indigo demonstrates higher reversibility and catalytic activity.

[0042] Between 0.1 and 0.6 mV s -1 The lithium-ion diffusion coefficient was calculated by CV test at different scan rates. Figure 15 a). The peak currents of all anodes and cathodes are linearly related to the square root of the scan rate. Figure 15 b). Li + The diffusion coefficient is calculated according to the following Randles-Sevcik equation: I p =2.69×10 5 n 1.5 AD0.5Li + C Li + v 0.5 Where I p This represents the peak current, n is the number of electrons in the reaction (for Li batteries, n is typically 2), and A represents the effective electrode area of ​​1.44 cm². 2 Lithium-ion diffusion coefficient of DLi, C Li + Li represents the electrolyte + The concentration is v, and the scan rate is v. For example... Figure 15 As shown in b, based on the fitted I p / ν 0.5 The slope of the curve and Li + The positive correlation between diffusion coefficients was used to calculate the Li content of each sample. + Diffusion coefficient. N-MPC@FeCo / Indigo exhibits a higher lithium-ion diffusion coefficient, further demonstrating its faster redox reaction kinetics.

[0043] Figure 16Electrochemical impedance spectroscopy (EIS) analysis of N-MPC@FeCo / Indigo, NC@FeCo / Indigo, MPC@FeCo / Indigo, and N-MPC / Indigo composites revealed that the N-MPC@FeCo / Indigo composite exhibited low impedance across the entire frequency range, particularly in the low-frequency region, indicating low interfacial charge transfer resistance. This suggests high conductivity and a greater number of electrochemically active sites, facilitating rapid electron and ion transport. Compared to other materials, N-MPC@FeCo / Indigo exhibited a smaller semi-circular impedance arc, indicating low charge transfer resistance and superior conductivity. The excellent response in the low-frequency region further demonstrates its high kinetic efficiency in electrochemical reactions, effectively improving charge-discharge efficiency and reaction rates. Therefore, N-MPC@FeCo / Indigo possesses significant advantages and high application potential in battery and catalysis applications.

[0044] Figure 17 Rate testing results of lithium-ion batteries assembled using N-MPC@FeCo / Indigo, NC@FeCo / Indigo, MPC@FeCo / Indigo, and N-MPC / Indigo cathode materials are presented. MPC@FeCo / Indigo exhibited excellent stability and high specific capacity in electrochemical cycling performance testing. While all materials showed varying degrees of capacity decay at different cycle counts, N-MPC@FeCo / Indigo maintained high stability, especially at high rates. Its initial specific capacity exceeded 170.6 mAh / g, and the decay was minimal after multiple cycles, demonstrating good cycling stability. Furthermore, when the current density recovered to 0.2C, the specific capacity recovery rate of N-MPC@FeCo / Indigo reached 91.0%, further demonstrating the material's high reversibility and strong kinetic response. These superior properties make N-MPC@FeCo / Indigo an ideal material for battery applications, particularly in high-efficiency energy storage devices.

[0045] Figure 18 Electrochemical performance of lithium batteries assembled using cathode materials of N-MPC@FeCo / Indigo, NC@FeCo / Indigo, MPC@FeCo / Indigo, and N-MPC / Indigo. Figure 18 The experiment demonstrated the electrochemical performance of pure indigo in a battery. Its initial specific capacity was only 80 mAh / g, and it rapidly decayed to below 20 mAh / g after 100 cycles, indicating that pure indigo materials suffer from significant poor conductivity and solubility issues, failing to meet the requirements for long-cycle battery use. Therefore, optimizing the material structure and performance to address these shortcomings becomes particularly important. Figure 18 The results in step b show that N-MPC@FeCo / Indigo, as a support, significantly improves the electrochemical performance of lithium indigo batteries. The N-MPC@FeCo / Indigo composite material provides more conductive pathways and a stable structure, enabling indigo to maintain a higher specific capacity during charge and discharge, and effectively alleviating the solubility problem of indigo. Compared with pure indigo, the composite material has a higher specific capacity and maintains lower degradation during cycling, demonstrating excellent cycle stability. Figure 19 The reaction mechanism was demonstrated, showing that N-MPC@FeCo / Indigo enhances the redox reaction of indigo through its nitrogen doping and metal catalysis, thereby effectively improving the overall performance of the battery. This mechanism not only improves the battery's conductivity but also enhances its stability during long-term use.

[0046] Figure 20 , 21 This further validates the role of N-MPC@FeCo / Indigo in lithium indigo batteries. The specific capacity and cycle performance of the N-MPC@FeCo / Indigo composite material are significantly better than those of pure indigo. It exhibits less specific capacity decay, better charge-discharge efficiency, and longer cycle life. Its initial specific capacity is only 140 mAh / g, which rapidly decays to about 75 mAh / g after 100 cycles. Figure 21 The electrochemical stability of the composite material was demonstrated. At a charge / discharge rate of 0.5C, N-MPC@FeCo / Indigo maintained a high specific capacity, proving its excellent high-rate performance and reversibility.

[0047] Figure 22The electrochemical performance of lithium-ion batteries assembled using the cathode material of Example 2 was demonstrated. The electrochemical performance of pure sodium indigo disulfonate in the battery was exhibited. Its initial specific capacity was only 40 mAh / g, and it rapidly decayed to below 20 mAh / g after 50 cycles, indicating that pure sodium indigo disulfonate material has significant poor conductivity and solubility problems, failing to meet the requirements for long-cycle use. Therefore, optimizing the material structure and performance to address these shortcomings is particularly important. The results show that N-MPC@FeCo / Indigo Carmine as a carrier significantly improves the electrochemical performance of lithium-ion pure sodium indigo disulfonate batteries. The N-MPC@FeCo / Indigo Carmine composite material provides more conductive pathways and a stable structure, enabling pure sodium indigo disulfonate to maintain a higher specific capacity during charge and discharge, and effectively alleviating the solubility problem of pure sodium indigo disulfonate. Compared with pure sodium indigo disulfonate, the composite material has a higher specific capacity and maintains lower decay during cycling, showing excellent cycle stability. The ability to maintain a high specific capacity demonstrates its good high-rate performance and reversibility. This demonstrates the excellent overall performance of this structure for indigo-based compounds.

[0048] In summary, cyclic voltammetry (CV) tests on the N-MPC@FeCo indigo-based composite cathode material demonstrate its high electrochemical activity and low electrochemical polarity, indicating that it maintains good stability and high efficiency during long-term charge-discharge processes. Furthermore, lithium-ion diffusion coefficient analysis reveals that the material exhibits high kinetic response, making it suitable for high-efficiency energy storage and battery applications.

[0049] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for preparing a cathode composite material for lithium-indigo energy storage batteries, characterized in that, Includes the following steps: S1: Biomass carbon source, nitrogen source, pore-forming agent, iron source and cobalt source are mixed and loaded into a ball mill, ball-milled in ethanol, and dried to obtain a precursor containing FeCo nano-alloys; S2: The precursor obtained in step S1 is calcined, washed, and dried in an inert gas atmosphere to obtain nitrogen-doped iron-cobalt nanoalloy porous biomass conductive carbon. S3: The nitrogen-doped iron-cobalt nanoalloy porous biomass conductive carbon obtained in step S2 is mixed with the cathode active material, and then the cathode composite material is obtained by high-temperature melting and calcination under an inert gas atmosphere.

2. The preparation method according to claim 1, characterized in that, In step S1, the biomass carbon source includes one of guar gum, creatine, coconut shell, sawdust, rice husk, and corn cob. The nitrogen source includes one of dicyandiamide, urea, cyanide, amine compounds, amino acids, and nitrogen compounds; The pore-forming agent includes one of sodium chloride, potassium chloride, calcium chloride, sodium hydroxide, zinc chloride, phosphoric acid, sulfuric acid, calcium hydroxide, sodium carbonate, and silica gel. The iron source includes one of ferric nitrate, ferric oxide, ferric chloride, ferric sulfide, and potassium ferricyanide; The cobalt source includes one of cobalt nitrate, cobalt oxide, cobalt chloride, cobalt sulfide, and cobalt salts.

3. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of iron in the biomass carbon source, nitrogen source, pore-forming agent, and iron source to cobalt in the cobalt source is 4.0:4.0:5.0:0.2:0.

211.

4. The preparation method according to claim 1, characterized in that, In step S1, the ball milling time is 8-18 hours.

5. The preparation method according to claim 1, characterized in that, In step S1, the drying temperature is 60-80℃ and the time is 20-24h.

6. The preparation method according to claim 1, characterized in that, In step S2, the inert gas is one or both of nitrogen and argon. The calcination temperature is 800-990℃, the holding time is 1-3h, and the heating rate is 3-6℃ / min.

7. The preparation method according to claim 1, characterized in that, In step S3, the inert gas is one or both of nitrogen and argon. The parameters for the high-temperature melting and calcination method are as follows: calcination temperature is 390-405℃, holding time is 1-3h, and heating rate is 3-6℃ / min.

8. The preparation method according to claim 1, characterized in that, In step S3, the cathode active material is an indigo-based compound.

9. A cathode composite material prepared by the preparation method according to any one of claims 1-8, characterized in that, The cathode composite material is composed of nitrogen-doped iron-cobalt nanoalloy porous biomass conductive carbon and cathode active material. The nitrogen-doped iron-cobalt nanoalloy porous biomass conductive carbon has a core-shell structure, with the core material being iron-cobalt nanoalloy and the shell material being nitrogen-doped porous biomass conductive carbon.

10. The application of the cathode composite material of claim 9 in a lithium-indigo energy storage battery.

Images