A method for preparing a composite additive for lead-carbon batteries

Abstract

The present application relates to lead-carbon battery technology, and aims to provide a preparation method of a composite additive for a lead-carbon battery. A composite additive for a lead-carbon battery is provided, which has a multi-layer coated composite structure of stable three-dimensional combination of active sites-carbon rods-graphene: Bi / Bi2O3 nanoparticles are confined in carbon nanorods derived from metal-organic frameworks (MOFs) and tightly embedded with the carbon matrix, and the formed embedding body is coated with a conductive graphene network. A three-dimensionally stable combined multi-layer coated composite structure is constructed by an in-situ growth-confined pyrolysis strategy; effectively solves the problem that the active material is easy to fall off and migrate in the charge and discharge cycle due to weak interface combination of traditional composite materials, balances the inhibition of negative electrode sulfation and the regulation of hydrogen evolution side reaction; significantly improves the cycle stability and service life of the battery under high rate partial state of charge; is easy to scale production and application, and has significant practical value.

Description

Technical Field

[0001] This invention relates to the field of lead-carbon battery technology, and specifically to a method for preparing a graphene@carbon@bismuth / bismuth oxide composite additive for lead-carbon batteries. Background Technology

[0002] Lead-carbon batteries effectively suppress sulfation at the negative electrode by introducing carbon materials, thereby improving cycle life at high-rate partial state of charge (HRPSoC). This improvement makes them promising for applications in hybrid electric vehicles, new energy storage, and grid peak shaving. However, the addition of carbon materials also reduces the hydrogen evolution overpotential at the negative electrode, exacerbating the hydrogen evolution reaction during charging. Long-term operation may lead to electrolyte drying, affecting battery life and reliability.

[0003] To balance the inhibitory effect of carbon materials on sulfation of the negative electrode and the hydrogen evolution side reaction they induce, existing technologies typically add composite additives of carbon materials and metals or their oxides (such as lead / lead oxide) with high hydrogen evolution overpotential to the negative electrode. These composites aim to utilize the carbon materials to maintain conductivity and cycle stability, while simultaneously using the metal components to increase the hydrogen evolution overpotential, thereby mitigating the hydrogen evolution reaction. However, traditional carbon materials (such as activated carbon, carbon black, and graphite) have strong surface chemical inertness and limited affinity for metals like lead, resulting in uneven distribution and weak binding of active components in the prepared composites. During actual battery charge and discharge processes, this structure easily leads to the separation of active materials from the carbon support, exposing hydrogen evolution active sites and causing uneven dispersion of additives in the negative electrode, ultimately affecting the stable performance of the battery.

[0004] Therefore, developing a novel composite additive that is structurally stable, tightly integrated, and can synergistically leverage the conductivity advantages of carbon materials and the high hydrogen evolution overpotential metal function has become the key to improving the overall performance of lead-carbon batteries. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a composite additive for lead-carbon batteries, specifically a graphene@carbon@bismuth / bismuth oxide composite additive.

[0006] To solve the technical problem, the technical solution adopted by this invention is as follows:

[0007] A composite additive for lead-carbon batteries is provided, the composite additive having a multilayered coated composite structure with a three-dimensional stable combination of active sites-carbon rods-graphene: Bi / Bi2O3 nanoparticles are confined in carbon nanorods derived from metal-organic frameworks (MOFs) and tightly intercalated with their carbon matrix, and the exterior of the formed intercalation is coated with a conductive graphene network.

[0008] The present invention also provides a method for preparing the composite additive, comprising the following steps:

[0009] (1) The bismuth-based metal-organic framework precursor solution and the graphene oxide dispersion were mixed evenly and subjected to a solvothermal reaction to allow the bismuth-based MOF to grow in situ on the surface of graphene oxide; the solid product was separated, washed, and vacuum dried to obtain the bismuth-based MOF@graphene oxide composite material.

[0010] (2) The composite material is heat-treated in an inert atmosphere to carbonize the organic components and partially reduce the graphene oxide to form a conductive network. At the same time, the bismuth component is converted into a bismuth / bismuth oxide composite, and finally the composite additive is obtained.

[0011] As a preferred embodiment of the present invention, in step (1), the bismuth source, the organic ligand and an appropriate amount of solvent are dissolved and mixed evenly under stirring conditions to obtain a clear precursor solution; the bismuth source is bismuth nitrate pentahydrate; the organic ligand is trimesic acid; the solvent is methanol, N,N-dimethylformamide, or a mixture of both.

[0012] As a preferred embodiment of the present invention, in the reaction system of step (1), the mass ratio of bismuth nitrate pentahydrate: organic ligand: graphene oxide is 150:750:4~30; the solvothermal reaction temperature is 120 °C and the reaction time is 24 h.

[0013] As a preferred embodiment of the present invention, in step (1), the solid reaction product is washed several times with methanol and deionized water, and then dried under vacuum at 60°C for 4 to 12 hours.

[0014] As a preferred embodiment of the present invention, in the composite material obtained in step (1), the bismuth-based MOF has a configuration of CAU-17.

[0015] As a preferred embodiment of the present invention, in step (2), the inert atmosphere refers to an atmosphere of argon or nitrogen; the heat treatment refers to heating to 500-800°C at a rate of 2-10°C / min and holding for 1-4 hours; and then naturally cooling to room temperature after the holding period.

[0016] The present invention further provides the application of the aforementioned composite additive as a negative electrode additive in lead-carbon batteries.

[0017] The present invention further provides a method for preparing a negative electrode green plate for a lead-carbon battery, comprising the following steps: using the composite additive as a negative electrode additive, mixing it evenly with lead powder, barium sulfate, humic acid, sodium lignosulfonate and short fibers; then adding deionized water and dilute sulfuric acid in sequence and stirring evenly to obtain a negative electrode slurry, controlling the amount of composite additive in the negative electrode slurry to be in the range of 0.3-2.0% (wt.); and then performing coating, acid impregnation and curing treatments to obtain the negative electrode green plate for a lead-carbon battery.

[0018] The present invention further provides a lead-carbon battery, wherein the negative electrode of the lead-carbon battery is obtained by formation of a negative electrode green plate, and the negative electrode green plate contains the aforementioned composite additive.

[0019] Description of the invention principle:

[0020] 1. This invention addresses the problem that the simple combination of carbon material additives and metal components with high hydrogen evolution overpotential in the negative electrode of lead-carbon batteries results in weak interfacial bonding, poor dispersibility, and easy separation during cycling, leading to unsustainable hydrogen evolution suppression effect and battery performance degradation. It proposes a preparation strategy of "in-situ growth-confined pyrolysis".

[0021] This strategy first utilizes the functional groups on the surface of graphene oxide to guide the in-situ growth of bismuth-based MOFs, constructing a molecular-level composite precursor; subsequently, it undergoes high-temperature heat treatment under an inert atmosphere. During this process, the organic ligands of the MOF are carbonized to form a carbon matrix supporting bismuth species, and the graphene oxide is partially reduced and its bismuth content is repaired. 2 The carbon conjugated structure forms a conductive network, while the bismuth component is transformed in situ into bismuth / bismuth oxide composite nanoparticles within the confined space, ultimately forming a stable multilayer structure of "reduced graphene oxide-coated carbon nanorods supporting bismuth / bismuth oxide". These steps are indispensable and cannot be reversed.

[0022] 2. In this invention, the active components are uniformly anchored and firmly bonded in the carbon carrier through the synergy of precursor design and heat treatment process, so that the composite material has excellent conductivity, structural stability and high hydrogen evolution overpotential at the same time, thereby synergistically suppressing the sulfation and hydrogen evolution reaction of the negative electrode and improving the HRPSoC cycle life of lead-carbon battery.

[0023] Compared with the prior art, the advantages of the present invention are as follows:

[0024] 1. This invention abandons the traditional method of simple physical mixing or surface loading of carbon materials with metals / metal oxides. Instead, it constructs a multilayered composite structure of "reduced graphene oxide (rGO) coated carbon matrix (C-nanorods) supporting bismuth / bismuth oxide (Bi / Bi2O3) nanoparticles" through an "in-situ growth-confined pyrolysis" strategy. In this structure, Bi / Bi2O3 nanoparticles are confined within MOF-derived carbon nanorods and tightly integrated with the carbon matrix. The outer layer is then coated with a conductive graphene network, forming a three-dimensional stable bond of "points (active sites) - lines (carbon rods) - surfaces (graphene)". This structure, through the dual effects of chemical bonding and physical confinement, greatly enhances the interfacial bonding between the high hydrogen evolution overpotential active component (bismuth / bismuth oxide) and the carbon support, effectively solving the problem of easy detachment and migration of active materials during charge-discharge cycles caused by weak interfacial bonding in traditional composite materials.

[0025] 2. Utilizing the abundant oxygen-containing functional groups on the surface of graphene oxide (GO) as nucleation sites for the in-situ growth of bismuth-based MOF crystals, uniform synthesis of the precursor was achieved at the molecular level. After heat treatment, bismuth species were transformed in-situ into nanoscale Bi / Bi₂O₃ composites within a confined space and highly uniformly dispersed throughout the carbon support. This microstructure allows the excellent conductivity and sulfation suppression capabilities of the carbon material to be tightly combined and synergistically utilized with the high hydrogen evolution overpotential characteristics of the bismuth-based material at the microscale, thereby more effectively balancing the suppression of sulfation at the negative electrode and the regulation of hydrogen evolution side reactions.

[0026] 3. Thanks to the stable, uniform, and tightly bonded composite structure described above, the additive prepared in this invention maintains structural integrity and long-lasting function during long-term charge-discharge cycles. The continuous conductive network constructed from carbon materials and graphene ensures excellent charge transport at the negative electrode; the firmly anchored Bi / Bi2O3 particles continuously provide a high and stable hydrogen evolution overpotential, effectively suppressing the hydrogen evolution side reaction during water electrolysis and slowing down electrolyte drying; simultaneously, the inhibitory effect of carbon materials on lead sulfate crystals is stably maintained. The synergistic effect of these three factors fundamentally alleviates the capacity decay and shortened lifespan problems caused by accelerated hydrogen evolution and additive failure in traditional lead-carbon batteries, significantly improving the cycle stability and lifespan of the battery at high-rate partial state of charge.

[0027] 4. The preparation method described in this invention has clear steps and well-defined process parameters (such as GO concentration, pyrolysis temperature, and time). By controlling the precursor composition and heat treatment conditions, the final composite structure, composition, and properties can be controlled. This method uses readily available raw materials, requires no complex or expensive equipment, has good compatibility with existing lead-carbon battery anode plate manufacturing processes, and requires only a small amount (0.3 wt.%–2.0 wt.%), making it easy to scale up production and promote application, thus possessing significant practical value. Attached Figure Description

[0028] Figure 1 XRD patterns of CAU-17 and composite materials with different proportions of graphene oxide.

[0029] In the figure, (a) shows the result before and after annealing, and (b) shows the result after annealing.

[0030] Figure 2 SEM images of different samples.

[0031] In the figure, (a) and (b) show the morphology of pure phase CAU-17 at different magnification ratios; (c) shows the SEM image of CAU-17 after annealing; (d)-(h) show the SEM morphology of the composite material rGO@C@Bi / Bi2O3 obtained after adding 2 ml, 5 ml, 7 ml, 10 ml and 15 ml of graphene oxide and annealing, respectively; the magnified effect of the content in the red dashed box in (f) is shown in Figure (i).

[0032] Figure 3 TEM images and EDS surface scan results for different samples.

[0033] In the figure, (a)-(c) are TEM images of the composite material obtained after adding 2 ml of graphene oxide and annealing; (d)-(f) are TEM images of the composite material obtained after adding 10 ml of graphene oxide and annealing; (g, h) are the EDS elemental distribution maps of the two samples mentioned above.

[0034] Figure 4 Cyclic voltammetry (CV) curves obtained after formation of the negative electrode plates prepared for application examples 1 and 2.

[0035] Figure 5 The results show the high-rate partial state of charge (HRPSoC) cycle life test results at 1C rate after assembling batteries based on the negative plates prepared in application examples 1, 2 and 3. Detailed Implementation

[0036] This invention proposes a method for preparing a graphene@carbon@bismuth / bismuth oxide composite additive. By constructing a multilayer coating structure, the binding force and interfacial compatibility between the components are enhanced. The aim is to achieve uniform loading and firm bonding of bismuth / bismuth oxide on a carbon support, thereby effectively controlling hydrogen evolution behavior while suppressing sulfation, and improving the cycle stability and service life of lead-carbon batteries.

[0037] 1. To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described below in conjunction with the accompanying drawings and implementation examples.

[0038] Example 1

[0039] (1) Weigh out pyromellitic acid (H3BTC, 750 mg) and bismuth nitrate pentahydrate (Bi(NO3)3·5H2O, 150 mg), add them to a beaker, then add 60 ml of methanol, and stir at room temperature until completely dissolved to obtain a clear solution, which is the bismuth-based metal-organic framework precursor solution. Then add 2 ml of 2 mg / ml graphene oxide (GO) dispersion to the solution and continue stirring for 30 min.

[0040] (2) The mixed solution from step (1) was transferred to a 100 ml stainless steel reactor lined with polytetrafluoroethylene, sealed, and placed in an oven at 120°C for 24 h. After the reaction was completed, the system was allowed to cool naturally to room temperature. The solid reaction product was collected by centrifugation and washed several times with methanol and deionized water. The product was then placed in a vacuum oven and dried under vacuum at 60°C for 4 h to obtain the CAU-17@rGO sample.

[0041] (3) The CAU-17@rGO sample obtained in step (2) was placed in a tube furnace and heated to 600°C at a heating rate of 10°C / min under an argon atmosphere. After heat treatment for 2 h, it was naturally cooled to room temperature. During this process, the MOF organic ligands were carbonized to form a carbon matrix containing bismuth species. Graphene oxide was partially reduced to a reduced graphene oxide conductive network. At the same time, the bismuth component was converted in situ into bismuth / bismuth oxide composite nanoparticles in the confined space, and finally a multilayer structure material of "reduced graphene oxide coated carbon nanorods loaded with bismuth / bismuth oxide" was formed, denoted as 2ml-rGO@C@Bi / Bi2O3.

[0042] Example 2

[0043] (1) Weigh out pyromellitic acid (H3BTC, 750 mg) and bismuth nitrate pentahydrate (Bi(NO3)3·5H2O, 150 mg), add them to a beaker, then add 60 ml of N,N-dimethylformamide, and stir at room temperature until completely dissolved to obtain a clear solution, which is the bismuth-based metal-organic framework precursor solution. Then add 5 ml of 2 mg / ml graphene oxide (GO) dispersion to the solution and continue stirring for 30 min.

[0044] (2) The mixed solution from step (1) was transferred to a 100 ml stainless steel reactor lined with polytetrafluoroethylene, sealed, and placed in an oven at 120°C for 24 h. After the reaction was completed, the system was allowed to cool naturally to room temperature. The solid reaction product was collected by centrifugation and washed several times with methanol and deionized water. The product was then placed in a vacuum oven and dried under vacuum at 60°C for 4 h to obtain the CAU-17@rGO sample.

[0045] (3) The CAU-17@rGO sample obtained in step (2) was placed in a tube furnace and heated to 500°C at a heating rate of 2°C / min under an argon atmosphere. After heat treatment for 4 h, it was naturally cooled to room temperature. During this process, the MOF organic ligands were carbonized to form a carbon matrix containing bismuth species. Graphene oxide was partially reduced to a reduced graphene oxide conductive network. At the same time, the bismuth component was converted in situ into bismuth / bismuth oxide composite nanoparticles within the confined space, ultimately forming a multilayer structure material of "reduced graphene oxide coated carbon nanorods loaded with bismuth / bismuth oxide", denoted as 5ml-rGO@C@Bi / Bi2O3.

[0046] Example 3

[0047] (1) Weigh out pyromellitic acid (H3BTC, 750 mg) and bismuth nitrate pentahydrate (Bi(NO3)3·5H2O, 150 mg), add them to a beaker, and then add 60 ml of a mixed solution of methanol and N,N-dimethylformamide (volume ratio 1:1). Stir at room temperature until completely dissolved to obtain a clear solution, which is the bismuth-based metal-organic framework precursor solution. Then add 7 ml of 2 mg / ml graphene oxide (GO) dispersion to the solution and continue stirring for 30 min.

[0048] (2) The mixed solution from step (1) was transferred to a 100 ml stainless steel reactor lined with polytetrafluoroethylene, sealed, and placed in an oven at 120°C for 24 h. After the reaction was completed, the system was allowed to cool naturally to room temperature. The solid reaction product was collected by centrifugation and washed several times with methanol and deionized water. The product was then placed in a vacuum oven and dried under vacuum at 60°C for 8 h to obtain the CAU-17@rGO sample.

[0049] (3) The CAU-17@rGO sample obtained in step (2) was placed in a tube furnace and heated to 600°C at a heating rate of 6°C / min under a nitrogen atmosphere. After heat treatment for 4 h, it was naturally cooled to room temperature. During this process, the MOF organic ligands were carbonized to form a carbon matrix containing bismuth species. Graphene oxide was partially reduced to a reduced graphene oxide conductive network. At the same time, the bismuth component was converted in situ into bismuth / bismuth oxide composite nanoparticles in the confined space, and finally a multilayer structure material of "reduced graphene oxide coated carbon nanorods loaded with bismuth / bismuth oxide" was formed, denoted as 7ml-rGO@C@Bi / Bi2O3.

[0050] Example 4

[0051] (1) Weigh out pyromellitic acid (H3BTC, 750 mg) and bismuth nitrate pentahydrate (Bi(NO3)3·5H2O, 150 mg), add them to a beaker, then add 60 ml of methanol, and stir at room temperature until completely dissolved to obtain a clear solution, which is the bismuth-based metal-organic framework precursor solution. Then add 10 ml of 2 mg / ml graphene oxide (GO) dispersion to the solution and continue stirring for 30 min.

[0052] (2) The mixed solution from step (1) was transferred to a 100 ml stainless steel reactor lined with polytetrafluoroethylene, sealed, and placed in an oven at 120°C for 24 h. After the reaction was completed, the system was allowed to cool naturally to room temperature. The solid reaction product was collected by centrifugation and washed several times with methanol and deionized water. The product was then placed in a vacuum oven and dried under vacuum at 60°C for 8 h to obtain the CAU-17@rGO sample.

[0053] (3) The CAU-17@rGO sample obtained in step (2) was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min under an argon atmosphere. After heat treatment for 2 h, it was naturally cooled to room temperature. During this process, the MOF organic ligands were carbonized to form a carbon matrix containing bismuth species. Graphene oxide was partially reduced to a reduced graphene oxide conductive network. At the same time, the bismuth component was converted in situ into bismuth / bismuth oxide composite nanoparticles within the confined space, ultimately forming a multilayer structure material of "reduced graphene oxide coated carbon nanorods loaded with bismuth / bismuth oxide", denoted as 10ml-rGO@C@Bi / Bi2O3.

[0054] Example 5

[0055] (1) Weigh out pyromellitic acid (H3BTC, 750 mg) and bismuth nitrate pentahydrate (Bi(NO3)3·5H2O, 150 mg), add them to a beaker, then add 60 ml of N,N-dimethylformamide, and stir at room temperature until completely dissolved to obtain a clear solution, which is the bismuth-based metal-organic framework precursor solution. Then add 15 ml of 2 mg / ml graphene oxide (GO) dispersion to the solution and continue stirring for 30 min.

[0056] (2) The mixed solution from step (1) was transferred to a 100 ml stainless steel reactor lined with polytetrafluoroethylene, sealed, and placed in an oven at 120°C for 24 h. After the reaction was completed, the system was allowed to cool naturally to room temperature. The solid reaction product was collected by centrifugation and washed several times with methanol and deionized water. The product was then placed in a vacuum oven and dried under vacuum at 60°C for 12 h to obtain the CAU-17@rGO sample.

[0057] (3) The CAU-17@rGO sample obtained in step (2) was placed in a tube furnace and heated to 800°C at a heating rate of 2°C / min under a nitrogen atmosphere. After heat treatment for 1 h, it was naturally cooled to room temperature. During this process, the MOF organic ligands were carbonized to form a carbon matrix containing bismuth species, and the graphene oxide was partially reduced to a reduced graphene oxide conductive network. At the same time, the bismuth component was converted in situ into bismuth / bismuth oxide composite nanoparticles in the confined space, and finally a multilayer structure material of "reduced graphene oxide coated carbon nanorods loaded with bismuth / bismuth oxide" was formed, denoted as 15ml-rGO@C@Bi / Bi2O3.

[0058] 2. Application method example:

[0059] The composite additive prepared in this invention, namely reduced graphene oxide-coated carbon nanorods loaded with bismuth / bismuth oxide (rGO@C@Bi / Bi2O3), can be used as a negative electrode additive. After preliminary screening, the composite additive is mixed evenly with lead powder, barium sulfate, humic acid, sodium lignin sulfonate, and short fibers according to conventional processing technology. Then, deionized water and dilute sulfuric acid are added sequentially and stirred evenly to obtain a negative electrode slurry. After coating, acid impregnation, and curing, a lead-carbon battery negative electrode green plate is obtained. The amount of composite additive in the negative electrode slurry is controlled within the range of 0.3% to 2.0% (wt.).

[0060] The conventional processing technology and the types and proportions of other materials in the negative electrode slurry can be selected by technicians based on the lead-carbon battery design scheme; this invention does not impose any special requirements.

[0061] Application Example 1

[0062] Different mass fractions of 2ml-rGO@C@Bi / Bi2O3 obtained in Example 1 (relative to lead powder: 0.3 wt.%, 0.5 wt.%, 0.6 wt.%, 0.9 wt.%, 1.0 wt.%, 1.5 wt.%) were used as negative electrode additives, along with lead powder (100 wt.%), acetylene black (0.2 wt.%), barium sulfate (0.83 wt.%), humic acid (0.46 wt.%), sodium lignin sulfonate (0.4 wt.%), short fibers (0.052 wt.%), deionized water (12.5 wt.%), and dilute sulfuric acid (7.9 wt.%, density 1.40 g·cm³). -3 The mixture was thoroughly mixed, coated onto a lead grid, and cured to obtain the negative electrode plate for a lead-acid battery. Samples with different mass fractions of additives were labeled as 2ml-0.3%, 2ml-0.5%, 2ml-0.6%, 2ml-0.9%, 2ml-1.0%, and 2ml-1.5%, respectively.

[0063] Application Example 2

[0064] Different mass fractions of 10 ml-rGO@C@Bi / Bi2O3 obtained in Example 4 (relative to lead powder: 0.3 wt.%, 0.6 wt.%, 0.9 wt.%, 1.0 wt.%, 1.5 wt.%, and 2.0 wt.%) were used as negative electrode additives, along with lead powder (100 wt.%), acetylene black (0.2 wt.%), barium sulfate (0.83 wt.%), humic acid (0.46 wt.%), sodium lignin sulfonate (0.4 wt.%), short fibers (0.052 wt.%), deionized water (12.5 wt.%), and dilute sulfuric acid (7.9 wt.%, density 1.40 g·cm³). -3 The mixture was thoroughly mixed, coated onto a lead grid, and cured to obtain the negative electrode plate for a lead-acid battery. Samples with different mass fractions of additives were labeled as 10ml-0.3%, 10ml-0.6%, 10ml-0.9%, 10ml-1.0%, 10ml-1.5%, and 10ml-2.0%, respectively.

[0065] Application Example 3

[0066] The 15 ml-rGO@C@Bi / Bi2O3 samples with different mass fractions obtained in Example 5 (0.3 wt.%, 0.6 wt.%, and 0.9 wt.% relative to lead powder, respectively) were used as negative electrode additives, along with lead powder (100 wt.%), acetylene black (0.2 wt.%), barium sulfate (0.83 wt.%), humic acid (0.46 wt.%), sodium lignin sulfonate (0.4 wt.%), short fibers (0.052 wt.%), deionized water (12.5 wt.%), and dilute sulfuric acid (7.9 wt.%, density 1.40 g·cm³). -3 The mixture was thoroughly mixed, coated onto a lead grid, and cured to obtain the negative electrode plate for a lead-acid battery. Samples with different mass fractions of additives were labeled as 15ml-0.3%, 15ml-0.6%, and 15ml-0.9%, respectively.

[0067] 3. Comparative Experiment and Results Description

[0068] Comparative Example 1

[0069] Lead powder (100 wt.%), barium sulfate (0.83 wt.%), humic acid (0.46 wt.%), sodium lignosulfonate (0.4 wt.%), short fibers (0.052 wt.%), deionized water (12.5 wt.%), and dilute sulfuric acid (7.9 wt.%, 1.40 g·cm³) were added. -3 After being thoroughly mixed, the mixture is coated onto a lead grid and cured to obtain the negative electrode green plate for a lead-acid battery. This is denoted as Control-0.0 wt.%.

[0070] Analysis of experimental results:

[0071] Figure 1 XRD patterns of CAU-17 and composites with different proportions of graphene oxide before and after annealing. Analysis shows that the introduction of graphene oxide does not change the crystal structure of CAU-17. After annealing, the Bi component in the material was successfully converted to Bi / Bi2O3, and the proportion of Bi in Bi / Bi2O3 gradually increased with the increase of graphene oxide content.

[0072] Figure 2 SEM morphologies of different samples are shown. (a) and (b) represent the original CAU-17, exhibiting a mixed morphology of sheet and rod shapes; (c) represents annealed CAU-17; and (d)-(h) represent the composite material rGO@C@Bi / Bi2O3 obtained after annealing with different volumes (2, 5, 7, 10, and 15 mL, all at a concentration of 2 mg / mL) of graphene oxide added in Examples 1-5. Morphological analysis revealed two key pieces of information: First, the introduction of only a small amount (2 mL) of graphene oxide significantly promotes the transformation of CAU-17 from a mixed sheet-rod state to a uniform rod structure; second, when the amount of graphene oxide added increases to 5 mL or more, the rod-shaped CAU-17 is further encapsulated and bundled by reduced graphene oxide, forming a composite material with a multilayer structure of "reduced graphene oxide-coated carbon nanorods supporting Bi / Bi2O3".

[0073] Figure 3 Images (a)-(c) in the figure show TEM images of 2 ml-rGO@C@Bi / Bi2O3. Images (b) and (c) are high-resolution TEM images showing two sets of clear lattice fringes with interplanar spacings of 0.328 nm and 0.319 nm, respectively, corresponding to the (012) crystal plane of metallic Bi and the (201) crystal plane of Bi2O3. Images (d)-(f) in the figure show TEM results of 10 ml-rGO@C@Bi / Bi2O3, with images (e) and (f) being high-resolution images, where the lattice fringes corresponding to the Bi(012) crystal plane can be observed more clearly. This phenomenon is consistent with the XRD analysis results, that is, with the increase of graphene oxide addition, the relative content of metallic Bi in Bi / Bi2O3 gradually increases. In addition, the EDS surface scan analysis results of 2 ml-rGO@C@Bi / Bi2O3 and 10 ml-rGO@C@Bi / Bi2O3 samples are also shown. Figure 3 The results from (g)-(h) confirm that C, Bi, and O elements are uniformly distributed in the composite material, and the distribution of each element is consistent with the morphology of the material.

[0074] Figure 4(a) and (b) show the cyclic voltammetry (CV) curves of the negative electrode plates prepared in Comparative Example 1 and Application Example 1, respectively, after formation. It is generally believed that graphene-based composite material additives can suppress hydrogen evolution to some extent compared to pure graphite phase additives, but compared to the blank negative electrode plate without carbon materials, the hydrogen evolution is more pronounced. Experimental data show that the 2ml-rGO@C@Bi / Bi2O3 additive introduced in this invention significantly inhibits the hydrogen evolution side reaction, with its hydrogen evolution current even lower than the blank control, demonstrating excellent inhibition effect; at the same time, this additive can also improve the redox reversibility of the negative electrode. Figure 4 Figures (c) and (d) show the CV curves of the negative electrode plates prepared in Comparative Example 1 and Application Example 2 after formation, respectively. When the additive content is less than 1.0 wt.%, the 10 ml-rGO@C@Bi / Bi2O3 additive exhibits similar abilities to 2 ml-rGO@C@Bi / Bi2O3 in inhibiting hydrogen evolution and regulating the kinetics of the negative electrode reaction. However, when the additive content is greater than 1.0 wt.%, the curve data shows irregular changes, indicating that excessive additive will lead to uneven dispersion in the electrode plate, thereby causing abnormal electrochemical performance.

[0075] Figure 5 Figures (a) and (b) show the high-rate partial state of charge (HRPSoC) lifetime test results of the batteries assembled based on the negative electrode plates prepared in Comparative Example 1 and Application Example 1, respectively. Compared with the control sample (Control - 0.0 wt.%) without any carbon material additives, the batteries with different proportions of 2 ml-rGO@C@Bi / Bi2O3 additive showed improved HRPSoC lifetimes. This is mainly due to the further suppression of the hydrogen evolution side reaction at the negative electrode and the promoting effect of the additive on the negative electrode kinetics. In addition, there is an optimal loading of 2 ml-rGO@C@Bi / Bi2O3 additive; when the critical value (approximately 0.5 wt.%) is exceeded, the battery lifetime decreases with increasing additive content, which may be related to the aggregation of the additive in the negative electrode active material. Figure 5 (c) and (d) show the HRPSoC lifetime of the batteries assembled based on the negative electrode plates prepared in Comparative Example 1 and Application Example 2, respectively. It can be seen that the effect of the 10 ml-rGO@C@Bi / Bi2O3 additive on the battery HRPSoC lifetime is similar to that of the 2 ml-rGO@C@Bi / Bi2O3 additive. When the additive content is 0.6 wt.%, the battery HRPSoC lifetime reaches its maximum (9,242 cycles), an improvement of approximately 142% compared to the control sample (3,826 cycles). Figure 5Figure (e) shows the HRPSoC lifetime test results of the battery assembled based on the negative electrode plates prepared in Comparative Example 1 and Application Example 3. Compared with Examples 1 and 2, the cycle life of this battery shows a significant downward trend, which is due to the increased hydrogen evolution side reaction caused by the increased graphene oxide content. Figure 5 Table (f) summarizes the impact of additive types and contents on battery HRPSoC lifespan in the form of a bar chart.

[0076] 4. Comparison and analysis with existing technologies:

[0077] (1) A Chinese patent document (application number CN202410926817.5) discloses a controllable preparation method for carbon-based negative electrode additives for lead-carbon batteries. This method uses a complexation precipitation coupled with a carbothermal reduction strategy to uniformly anchor lead particles on the surface of carbon materials, thereby achieving a tight bond between lead and carbon.

[0078] Compared with the technical solution described in that document, the present invention has the following substantial differences: First, the active component loaded in the present invention is bismuth / bismuth oxide (Bi / Bi2O3), rather than metallic lead. Bi / Bi2O3 has a higher hydrogen evolution overpotential than metallic lead, and is more advantageous in suppressing hydrogen evolution side reactions, making it more suitable for use as the negative electrode of lead-carbon batteries that require long-term suppression of hydrogen evolution. Second, the structural design of the present invention is more advanced: the Bi / Bi2O3 nanoparticles are not simply anchored on the surface of carbon materials, but are confined inside MOF-derived carbon nanorods, while being coated externally by a reduced graphene oxide network, forming a unique "core-shell" multilayer structure. This structure not only provides excellent conductivity through the outer graphene layer, but also more effectively prevents the active component from falling off and agglomerating during charge-discharge cycles through the physical confinement effect of the carbon nanorod matrix, resulting in structural stability far superior to surface-anchored composite materials. Furthermore, this invention achieves highly uniform distribution and robust integration of Bi / Bi2O3 in a carbon matrix through in-situ growth and confined pyrolysis of MOF precursors. The controllability and consistency of its microstructure are superior to those of the complexation precipitation method, which is beneficial for performance reproduction in large-scale production.

[0079] (2) Chinese patent document (application number CN202511269994.1) discloses a hierarchical porous carbon anode material with synergistic activity of nano-metals and its application in long-life lead-carbon batteries. The material uses carbon with a hierarchical porous structure of micropores, mesopores and macropores as the matrix, and uniformly loads nano-metal particles (such as Fe, Co, Sn, etc.) to suppress sulfation and reduce hydrogen evolution reaction.

[0080] Compared with the technical solution described in that document, this invention has the following substantial differences: Instead of employing a disordered physical composite of hierarchical porous carbon and metal particles, this invention constructs a regular multilayer structure with MOF-derived carbon nanorods as the core and reduced graphene oxide as the shell. In this structure, the active component Bi / Bi₂O₃ is confined within the carbon nanorods, forming a tight intercalation with the carbon matrix, while the external graphene network further encapsulates it, achieving a three-dimensional stable bond of "active site-carbon rod-graphene". This design not only provides an efficient electron transport path but also effectively prevents the migration and aggregation of the active component during long-term charge-discharge cycles through the dual effects of physical confinement and chemical bonding. In contrast, traditional hierarchical porous carbon and metal particle composite systems struggle to achieve such a uniform, robust, and ordered interfacial bond. Furthermore, the Bi / Bi₂O₃ selected in this invention possesses an extremely high hydrogen evolution overpotential. Combined with the unique confinement structure, it can suppress sulfation while more effectively slowing down electrolyte drying, thereby significantly improving the cycle stability of lead-carbon batteries under HRPSoC conditions.

[0081] It should be noted that the above embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A composite additive for lead-carbon batteries, characterized in that, The composite additive has a multilayered composite structure with a three-dimensional stable combination of active sites, carbon rods, and graphene: Bi / Bi2O3 nanoparticles are confined in carbon nanorods derived from metal-organic frameworks (MOFs) and tightly intercalated with their carbon matrix, and the exterior of the resulting intercalation is covered by a conductive graphene network.

2. The method for preparing the composite additive according to claim 1, characterized in that, Includes the following steps: (1) The bismuth-based metal-organic framework precursor solution and the graphene oxide dispersion were mixed evenly and subjected to a solvothermal reaction to allow the bismuth-based MOF to grow in situ on the surface of graphene oxide; the solid product was separated, washed, and vacuum dried to obtain the bismuth-based MOF@graphene oxide composite material. (2) The composite material is heat-treated in an inert atmosphere to carbonize the organic components and partially reduce the graphene oxide to form a conductive network. At the same time, the bismuth component is converted into a bismuth / bismuth oxide composite, and finally the composite additive is obtained.

3. The preparation method according to claim 2, characterized in that, In step (1), the bismuth source, organic ligand and appropriate amount of solvent are dissolved and mixed evenly under stirring to obtain a clear precursor solution; the bismuth source is bismuth nitrate pentahydrate; the organic ligand is trimesic acid; the solvent is methanol, N,N-dimethylformamide, or a mixture of both.

4. The method according to claim 2, characterized in that, In the reaction system of step (1), the mass ratio of bismuth nitrate pentahydrate: organic ligand: graphene oxide is 150:750:4~30.

5. The preparation method according to claim 2, characterized in that, In step (1), the solid reaction product is washed several times with methanol and deionized water, and then vacuum dried.

6. The preparation method according to claim 2, characterized in that, In the composite material obtained in step (1), the bismuth-based MOF has the configuration of CAU-17.

7. The preparation method according to claim 2, characterized in that, In step (2), the inert atmosphere refers to an atmosphere of argon or nitrogen; the heat treatment refers to heating to 500-800℃ at a rate of 2-10℃ / min and holding for 1-4 hours; after the holding period, naturally cooling to room temperature.

8. The application of the composite additive of claim 1 as a negative electrode additive for lead-carbon batteries.

9. A method for preparing a negative electrode plate for a lead-carbon battery, characterized in that, The process includes the following steps: using the composite additive described in claim 1 as a negative electrode additive, mixing it evenly with functional powder and fiber material; then adding deionized water and dilute sulfuric acid in sequence, stirring evenly to obtain a negative electrode slurry; and then subjecting it to coating, acid impregnation, and curing treatments to obtain a negative electrode plate for a lead-carbon battery.

10. A lead-carbon battery, characterized in that, The negative electrode of the lead-carbon battery is formed from a negative electrode green plate, and the negative electrode green plate contains the composite additive as described in claim 1.

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