Negative electrode material, preparation method and iron-air battery

Abstract

This invention relates to the field of electrochemical energy storage technology, specifically to a negative electrode material, its preparation method, and an iron-air battery. The negative electrode material includes an active material, functional additives, a conductive agent, and a binder. The active material and functional additives are added to a ball mill jar and ball-milled to obtain a composite powder. The conductive agent, binder, and the obtained composite powder are placed in a composite solvent to obtain a mixed slurry. The obtained mixed slurry is coated onto a current collector, dried, and rolled to obtain the negative electrode material. By simultaneously addressing passivation, hydrogen evolution, and expansion issues through a ZnS-Fe heterojunction, a capacity retention rate of >80% is achieved after 800 cycles.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, specifically to a negative electrode material, its preparation method, and an iron-air battery. Background Technology

[0002] Iron-air batteries, with their high theoretical energy density of approximately 1200 Wh / kg, abundant iron resources, low cost, and environmental friendliness, are considered candidates for next-generation large-scale energy storage technology. However, traditional iron-air batteries suffer from the following problems, hindering their practical application: 1. Negative electrode passivation: Iron easily forms an insulating FeOOH passivation layer in alkaline electrolytes, which blocks charge transport, leading to deactivation of active materials and capacity decay; 2. Hydrogen evolution side reaction (HER): Hydrogen evolution on the iron surface is severe under highly alkaline conditions, which reduces coulombic efficiency and energy density; 3. Structural pulverization and expansion: During the charge and discharge process, the volume expansion of iron oxidation-reduction is greater than 200%, which can easily lead to electrode cracking, structural collapse, and a sharp drop in cycle life.

[0003] Existing technologies have addressed the aforementioned problems by employing methods such as carbon-coated iron anodes, alloyed iron-based materials, and electrolyte additives, but these methods have significant drawbacks: 1. Patent CN103597655A / B discloses an iron electrode composed of carbonyl iron and metal sulfide or metal oxide additives, which can be further supplemented with organic sulfur additives such as alkathiols, dithiols, or thioethers to suppress hydrogen evolution reaction and improve discharge performance during the charging process of the iron electrode. However, this technology mainly adopts the method of physical mixing of sulfide particles and iron powder or adsorption at the interface of organic sulfur molecules, without forming a continuous and stable inorganic sulfide shell on the surface of iron particles, nor constructing a corresponding stress buffer structure for the volume change during the cycling process of the iron negative electrode.

[0004] 2. Patent CN117751468A discloses the addition of crystalline cubic zinc sulfide particles to the iron electrode of an alkaline iron battery, or the configuration of crystalline cubic zinc sulfide as a sulfide reservoir separate from the iron electrode, to control the release and loss of sulfides in the alkaline electrolyte. This patent recognizes that different ZnS crystal forms have different dissolution rates in strongly alkaline electrolytes and reduces the excessively rapid dissolution of sulfides by increasing the crystallinity of cubic ZnS. However, in this technology, ZnS still exists as independent particles or an external reservoir; the contact between ZnS and the iron active material is primarily physical, without forming a continuous heterogeneous interface between the iron core and the iron-doped ZnS shell.

[0005] 3. Patent CN120188282A discloses a solid additive formed by the agglomeration of fine metal sulfide particles, and the preparation of an iron anode by mixing this additive with iron active material powder, wherein the metal sulfide may include ZnS, FeS, Bi2S3, MoS2, or NiS, etc. This method can improve the dispersion and ion transport of sulfide additives by adjusting the particle size and porosity of agglomerated particles, but it still belongs to the particle-level physical mixing of iron active materials and sulfide additives, and it is difficult to form a uniform, continuous protective interface with electronic structure control capability on the surface of each iron particle.

[0006] In summary, passivation, hydrogen evolution, and expansion of iron anodes remain three major problems that cannot be solved simultaneously by existing technologies, and some existing methods are either too costly or have complex processes. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing single-modification schemes for iron anodes, which cannot simultaneously solve passivation, hydrogen evolution, and volume expansion. This invention provides an anode material, a preparation method, and an iron-air battery. By combining zinc sulfide (ZnS) with iron-based materials, the passivation, hydrogen evolution, and volume expansion problems of traditional iron anodes can be solved, effectively improving battery cycle life and energy efficiency.

[0008] To solve the above technical problems, the first objective of this invention is to provide a negative electrode material, wherein the negative electrode material is composed of an active substance, a functional additive, a conductive agent and a binder in a mass ratio of 6-9:1-3:1-1.5:1-1.5; The active substance is iron or zinc; The functional additive is at least one of zinc sulfide, iron sulfide, and lead sulfide. The conductive agent is at least one of carbon nanotubes, mesophase carbon microspheres, and carbon black. The adhesive is at least one of polyvinylidene fluoride and polytetrafluoroethylene.

[0009] Furthermore, the active substance is iron; the functional additive is zinc sulfide; and the conductive agent is carbon nanotubes. The adhesive is polyvinylidene fluoride.

[0010] The applicant discovered that ZnS can form a heterojunction structure with Fe, thereby reducing charge transfer resistance, inhibiting passivation of the Fe anode surface, reducing the formation of FeOOH, and regulating the hydrogen evolution reaction, thus increasing the hydrogen adsorption energy. Furthermore, the hard particles of ZnS can buffer the volume expansion of the Fe anode, resulting in better maintenance of electrode porosity after cycling.

[0011] Based on the above-mentioned anode materials, a second objective of this invention is to provide a method for preparing anode materials, comprising the following steps: S1. Preparation of composite powder by ball milling under inert atmosphere Weigh out the active material and functional additives according to the formula, add them to the ball mill jar; under nitrogen / argon inert protection, ball mill for 6-12 hours to obtain a uniform composite powder. Active substances and functional additives are added to a ball mill jar and ball milled to obtain composite powder. S2. Preparation of composite solvent and pulp activation: Prepare composite solvent, wherein the mass ratio of main solvent, interface activator and structure directing agent in composite solvent is 7-8:1.5-2.5:0.5-1.5; The composite powder, conductive agent, and binder obtained in step S1 are added to the composite solvent and stirred for 4-8 hours to construct an in-situ Fe-sulfide covalently bonded heterostructure. S3. Coating, drying, and roll forming: The mixed slurry obtained in step S2 is uniformly coated on the surface of the current collector, dried at 100-150℃ for 4-12 hours, and then rolled to obtain the negative electrode material.

[0012] Furthermore, the main solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, isopropanol, and cyclohexanone; The interface activator is selected from at least one of ethylenedithiol, 1,3-propanedithiol, thiomalic acid, cysteine, 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, triethylamine, triethanolamine, and ethylenediamine. The structure-directing agent is selected from at least one of hexadecyltrimethylammonium bromide, sodium citrate, and polyacrylic acid.

[0013] Further, the main solvent is N-methylpyrrolidone or N,N-dimethylformamide; the interface activator is 2-mercaptobenzimidazole or 2-mercaptobenzothiazole; and the structure directing agent is hexadecyltrimethylammonium bromide or sodium citrate.

[0014] The current collector is made of porous nickel foam, nickel foil, graphene-coated nickel foil, 316L stainless steel, or titanium mesh.

[0015] The applicant discovered that using the aforementioned combination of main solvent, interface activator, and structure directing agent can further promote the formation of Fe-ZnS heterojunctions on the Fe surface during stirring. Specifically, the thiol groups in the interface activator bond to the Fe surface, providing ion transfer channels for the formation of the Fe-ZnS heterostructure. Furthermore, the interface activator adsorbs Zn... 2+ , making S 2- Free. Free S 2-The Zn is transferred to the Fe surface via an interfacial activator. Furthermore, a structure-directing agent causes the cation heads to be oriented and adsorbed onto the ZnS{111} facet, forcing the Zn terminals to be exposed and matched with the Fe{110} crystal facet (lattice mismatch rate <2.5%), ultimately forming a covalently bonded heterojunction under solvothermal treatment.

[0016] Based on the above negative electrode materials and preparation methods, the third objective of this invention is to provide an iron-air battery, wherein the negative electrode material of the iron-air battery is the above negative electrode material or the negative electrode material prepared by the above preparation methods.

[0017] Furthermore, the positive electrode material of the iron-air battery is CoNiO. X / C, Fe-N4 / C or La 0.8 Sr 0.2 Co O3 ; The electrolyte material of the iron-air battery is KOH, NaOH or LiOH.

[0018] The beneficial effects of adopting the above technical solution in this invention are as follows: 1) Simultaneously addressing three major anode defects: The ZnS-Fe heterojunction reduces interfacial charge transfer impedance, resulting in a FeOOH passivation layer yield of less than 50%; the HER onset potential shifts negatively by 0.3V, significantly suppressing the hydrogen evolution side reaction; hard nano-ZnS particles buffer charge-discharge volume expansion, maintaining a stable electrode porosity of 30% after 800 cycles, with a porosity decay of less than 10%, achieving a porosity retention rate of 90%; the battery capacity retention rate after 800 cycles is >80%, with the optimal embodiment reaching 89%; 2) Extremely low interfacial charge transfer impedance: The composite solvent is used to construct covalently bonded heterojunctions in situ at low temperature, resulting in an initial interfacial charge transfer impedance as low as 0.84 Ω·cm. 2 The impedance increase after long-term cycling is much lower than that of traditional processes; 3) Simple process and low raw material cost: No high-temperature heat treatment is required throughout the process. Only conventional lithium battery preparation processes such as ball milling and liquid phase coating are used. Iron powder, nano ZnS, and carbon nanotubes are all industrially mass-produced raw materials, and the cost is much lower than carbon coating and precious metal modification schemes. 4) No secondary pollution and strong system stability: No soluble sulfides are added to the electrolyte, avoiding poisoning of the air cathode catalyst and release of toxic H2S gas, which greatly improves the long-cycle stability of the battery. Attached Figure Description

[0019] Figure 1 This is a SEM image of the Fe-ZnS anode obtained by the preparation method described in Example 1 of this invention; Figure 2 This is a SEM image of the Fe-ZnS anode obtained by the preparation method described in Comparative Example 1 of this invention; Figure 3 Impedance spectra of the Fe-ZnS anodes prepared in Example 1 and Comparative Example 1 of this invention; Figure 4 This is a comparison of the CV curves of Embodiment 2, Comparative Example 2, and Comparative Example 3 after 100 cycles. Figure 5 The following are the cycle capacity retention curves of Embodiment 2, Comparative Example 2, and Comparative Example 3 of the present invention at a 0.5C rate. Figure 6 This is a SEM image of the Fe-ZnS anode after 800 cycles in Example 2 of the present invention; Figure 7 This is a SEM image of the Fe-ZnS anode after 800 cycles in Comparative Example 2 of this invention. Figure 8 The impedance spectra of the Fe-ZnS anode before and after 50 cycles in Example 2 of the present invention are shown. Figure 9 The impedance spectra of the Fe-ZnS anode before and after 50 cycles in Comparative Example 2 of this invention are shown. Figure 10 The impedance spectra of the Fe-ZnS anode before and after 50 cycles in Comparative Example 3 of this invention are shown. Figure 11 Impedance spectra of Fe-ZnS anodes after 50 cycles in Examples 2, 2, and 3 of the present invention; Figure 12 The CV cycle diagrams show the hydrogen evolution potentials of the Fe-ZnS negative electrode labels prepared in Example 1 and Comparative Example 1 of this invention. Figure 13 The relative FeOOH content on the negative electrode surface after 800 cycles in Examples 2, 2, and 3 of this invention; Figure 14 The interface charge transfer impedance of Embodiment 2, Comparative Example 2, and Comparative Example 3 before and after 50 cycles of the present invention; Figure 15 The negative electrode porosity is shown in Embodiment 2, Comparative Example 2, and Comparative Example 3 before and after 800 cycles. Detailed Implementation

[0020] The present invention will be described in detail below with reference to the embodiments, but the present invention is not limited to these embodiments. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all purchased through commercial channels.

[0021] Example 1, a negative electrode material, wherein the Fe-ZnS negative electrode is prepared: S1. Preparation of composite powder by ball milling under inert atmosphere: Weigh iron powder and ZnS nanoparticles at a mass ratio of 8:2 and add them to a ball mill jar. The particle size range of ZnS nanoparticles is 50-200nm and the purity is ≥98%. Ball mill for 10 hours under argon protection. The ball-to-material ratio is 10:1-30:1, which is 20:1 in this example. The ball milling speed is 300-600rpm, which is 500rpm in this example. The composite powder is obtained. S2. Preparation of composite solvent and pulp activation: N-methylpyrrolidone (NMP), 2-mercaptobenzimidazole (MBI), and hexadecyltrimethylammonium bromide (CTAB) are mixed in a mass ratio of 7:1.5:1.5 to obtain a composite solvent; The composite powder was mixed with carbon nanotubes (CNTs) and polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1. The composite solvent was added at a ratio of 1g solid to 20g solvent. The mixture was stirred at 300-800rpm for 4-8h, or 600rpm for 6h in this example. After stirring, the mixture was allowed to stand at low temperature for 2h to construct Fe-sulfide covalently bonded heterostructures in situ and prepare a mixed slurry. S3, Coating, Drying, Roll Forming: Using 0.1g of mixed slurry / 1cm 2 The density of the current collector is coated onto the porous nickel foam and dried at 120℃ for 6 hours. After drying, it is rolled to a compacted density of 1.2-1.8 g / cm³. 3 In this example, it is 1.6 g / cm³. 3 To obtain the corresponding negative electrode sheet.

[0022] The SEM image of the Fe-ZnS anode prepared in Example 1 is shown below. Figure 1 Impedance spectrum (see) Figure 3 .

[0023] Comparative Example 1: Fe-ZnS anode prepared using conventional solvents The preparation method of Comparative Example 1 is the same as that of Example 1, except that only N-methylpyrrolidone is used as the solvent, and 2-mercaptobenzimidazole and hexadecyltrimethylammonium bromide are no longer added.

[0024] SEM image of the Fe-ZnS anode prepared in Comparative Example 1 is shown below. Figure 2 Impedance spectrum (see) Figure 3 ; Depend on Figure 1 and Figure 2 It can be seen that the negative electrode material prepared using the composite solvent of this invention has a more uniform distribution of Zn and S elements on the Fe surface. Figure 3 It can be seen that the negative electrode material prepared using the composite solvent of this invention has a significantly lower overall resistance, and the interfacial charge transfer impedance measured using Zview software with an impedance diagram is 0.84 Ω·cm. 2 .

[0025] Example 2: Assembly and performance testing of iron-air batteries The Fe-ZnS iron-based negative electrode prepared in Example 1 was cut into a shape that matched the battery clamp, with an effective negative electrode area of ​​2.50 cm². 2 The surface loading of Fe active material is 10.0 mg / cm³. 2 The thickness of the negative electrode after roll forming is 250±20μm.

[0026] This embodiment uses a porous carbon-supported cobalt-nickel oxide air cathode, denoted as CoNiO. X / C Air positive electrode, air positive electrode is made of CoNiO X The catalyst consists of conductive carbon and polytetrafluoroethylene binder in a mass ratio of 70:20:10, with a Co to Ni molar ratio of 1:2. The catalyst layer is supported on the surface of hydrophobic carbon paper, using a nickel mesh as the current collector. The catalyst layer density at the air cathode is 2.0 mg / cm³. 2 The effective area is 2.50cm². 2 The total electrode thickness is 350±20μm. The catalytic layer of the air cathode faces the membrane, and the hydrophobic gas diffusion layer faces the air side.

[0027] Polypropylene porous separator Celgard 3501 was cut to a size that could completely cover the negative electrode, with two separators used in each cell. Before assembly, the separator was pre-wetted in an alkaline aqueous electrolyte consisting of 6 M KOH and 0.1 M LiOH for 30 min.

[0028] An open-air battery structure with a clamp-on design is adopted, in which Fe-ZnS iron-based anode, two layers of Celgard 3501 separator, and CoNiO are sequentially placed. X / C Air positive electrode, so that the effective reaction areas of the negative electrode and the air positive electrode correspond to each other. Add 5.0 mL of the above electrolyte to the battery, fix the battery clamp and check that there is no direct contact between the electrodes and no electrolyte leakage.

[0029] After assembly, allow it to stand at 25±1℃ for 30 minutes before performing electrochemical tests: 1. Constant current cycling performance test Constant current charge-discharge tests were conducted using the Blue Battery Testing System. The mass of Fe active material in the negative electrode was used as the normalization benchmark for capacity and current. 1C was defined as 500 mA / gFe, and the mass current density corresponding to 0.5C was 250 mA / gFe.

[0030] In this embodiment, the mass of Fe active material in the negative electrode is 25.0 mg, the actual test current under 0.5C conditions is 6.25 mA, and the corresponding surface current density of the effective negative electrode area is 2.50 mA / cm². 2The charging cutoff voltage is 1.80V, and the discharging cutoff voltage is 0.70V. A 5-minute rest period is allowed between each charge and discharge cycle. Cycle capacity retention is calculated as the ratio of the discharge capacity in the nth cycle to the initial discharge capacity, using the following formula: Capacity retention rate = discharge capacity in the nth cycle ÷ discharge capacity in the first cycle × 100%.

[0031] Example 2: 800 constant current charge-discharge cycles were performed under the above 0.5C conditions, and the resulting capacity retention curve is shown below. Figure 5 As shown, the morphology of the negative electrode after cycling is as follows: Figure 6 As shown.

[0032] 2. Cyclic Voltmeter-Ammeter Test Cyclic voltammetry was performed using a three-electrode system. The Fe-ZnS anode prepared in Example 2 was used as the working electrode, the Hg / HgO electrode as the reference electrode, and the platinum mesh as the counter electrode. The electrolyte was a mixed solution of 6 M KOH and 0.1 M LiOH.

[0033] The Blue Battery testing system was used for testing at a temperature of 25±1℃, a scan potential range of -1.25 to -0.40V, and a scan rate of 5mV / s relative to the Hg / HgO reference electrode. The cycled negative electrodes were tested under the same conditions to compare the redox current response and hydrogen evolution initiation potential of each negative electrode. The test results are as follows: Figure 4 As shown.

[0034] 3. Electrochemical impedance spectroscopy Electrochemical impedance spectroscopy (EIS) uses the same three-electrode system and electrolyte as cyclic voltammetry (CVT). The negative electrode is tested before and after 50 cycles. Before testing, the electrode is left to stand at its open-circuit potential until the change in open-circuit potential does not exceed the specified range.

[0035] The impedance test frequency range is 10. 5 The frequency was ~0.05Hz, the AC disturbance amplitude was 5mV, and the test potential was the open circuit potential. The impedance data were fitted using an equivalent circuit of Rs-(Rct∥CPE)-W, where Rs represents the series resistance between the solution and the contact, Rct represents the interfacial charge transfer impedance, CPE represents the constant phase element, and W represents the diffusion impedance.

[0036] The fitted Rct is normalized according to the effective area of ​​the negative electrode, that is: Area normalization Rct = fitted resistance value × effective area of ​​negative electrode.

[0037] In this embodiment, the effective area of ​​the negative electrode is 2.50 cm². 2 The impedance spectra before and after 50 cycles are as follows: Figure 8As shown, the impedance results, along with those of Comparative Examples 2 and 3 after 50 cycles, are plotted together. Figure 11 middle.

[0038] Comparative Example 2: Iron-air battery with negative electrode prepared using conventional solvents An iron-air battery was assembled using the Fe-ZnS anode prepared in Comparative Example 1 instead of the Fe-ZnS iron-based anode in Example 2.

[0039] Aside from the different anode materials, Comparative Example 2 uses CoNiO X The composition of the air cathode, the molar ratio of Co to Ni, the catalyst layer formulation, the catalyst layer density, the effective area of ​​the air cathode, the gas diffusion layer, the current collector, the separator material and number of layers, the electrolyte composition and amount added, the battery structure, the assembly sequence, the standing time, and the test temperature are all the same as in Example 2.

[0040] The effective area of ​​the negative electrode in Comparative Example 2 is also 2.50 cm². 2 The surface loading of Fe active material was controlled at 10.0 mg / cm³. 2 Comparative Example 2 was subjected to constant current cycling tests according to the 0.5C rate definition, current calculation method, charge / discharge cutoff voltage, and resting conditions described in Example 2.

[0041] The three-electrode system, reference electrode, counter electrode, electrolyte, scan potential range, scan rate, impedance frequency range, AC perturbation amplitude, test potential, equivalent circuit, and area normalization method used in the cyclic voltammetry and electrochemical impedance spectroscopy tests of Comparative Example 2 were the same as those in Example 2. The CV cyclic voltammetry curves are shown below. Figure 4 As shown, the capacity retention curve obtained after 400 constant current charge-discharge cycles at 0.5C is as follows. Figure 5 As shown, the morphology of the negative electrode after cycling is as follows: Figure 7 As shown, the impedance spectra before and after 50 cycles are as follows: Figure 9 As shown.

[0042] Comparative Example 3: An iron-air battery composed of a commercially available Fe negative electrode. A commercially available iron sheet polished with 2000-grit sandpaper was used as the negative electrode to replace the Fe-ZnS negative electrode prepared in Comparative Example 1. The assembly of an iron-air battery was identical to that of Comparative Example 2, except for the negative electrode material. The CV cyclic voltammetry curves are shown below. Figure 4 As shown, the capacity retention curve obtained after 100 constant current charge-discharge cycles at 0.5C is as follows. Figure 5 As shown, the impedance spectra before and after 50 cycles are as follows: Figure 10 As shown.

[0043] Example 2, Determination of FeOOH content, charge transfer impedance and electrode porosity of negative electrodes in Comparative Examples 2 and 3: 1. After 800 cycles, the FeOOH content on the surface of the negative electrode was determined by acid washing and weighing method. The electrode was washed sequentially with deionized water and anhydrous ethanol, and then vacuum-dried at 60°C to constant weight. The mass before acid washing was recorded as m0. The acid washing solution was prepared by diluting 500 mL of concentrated hydrochloric acid, 3.5 g of hexamethylenetetramine, and deionized water to a final volume of 1000 mL. The electrode was placed in 50 mL of the acid washing solution and gently shaken at 20–25°C for 60 s. After removal, it was immediately rinsed thoroughly with deionized water, then rinsed with anhydrous ethanol, and vacuum-dried at 60°C to constant weight. The mass after acid washing was recorded as m1. A blank test was performed using a non-circulated electrode with the same composition and area, following the same procedure. The mass loss per unit area during acid washing was recorded as B.

[0044] mFeOOH=(m0-m1)-BA Where A is the effective area of ​​the electrode. Based on the pre-cycle active material mass mactive, the FeOOH equivalent mass fraction is calculated using the following formula: wFeOOH = (mFeOOH / mactive) × 100% Each group used three independent electrodes for parallel testing, and the results are expressed as mean ± standard deviation. Since small amounts of other iron oxides or hydroxides may be removed during the pickling process, the results are used to characterize the relative content of FeOOH-type acid-soluble passivation products on different negative electrode surfaces. Pickling of ZnS electrodes was performed under ventilated conditions, and the results are as follows... Figure 13 As shown.

[0045] 2. Measurement of charge transfer impedance Electrochemical impedance spectroscopy (EIS) was performed on the prepared iron-air battery using an electrochemical workstation. Before testing, the battery was allowed to stand at 25±1℃ until its open-circuit potential stabilized, with a standing time of at least 30 minutes. Using the battery's open-circuit potential as the DC bias, a sinusoidal AC perturbation signal with an amplitude of 5 mV was applied, and the test frequency range was 1.0 × 10⁻⁶. 5 ~5.0×10 -2 Hz. The batteries were tested before and after 50 cycles respectively; the batteries after cycling were adjusted to the same state of charge as before cycling before testing and left to stand until the open circuit potential stabilized.

[0046] The obtained impedance data uses the equivalent circuit R S Fitting is performed using -(Rct∥CPE)-W, where R S Rct is the ohmic resistance generated by the electrolyte, diaphragm, and electrode contact; Re is the charge transfer resistance at the electrode / electrolyte interface; CPE is the constant-phase element; and W is the Warburg diffusion impedance. Rct is characterized by the intercept of the Nyquist curve in the high-frequency region with the real axis. SRct is characterized by the semicircle diameter obtained from fitting in the high and mid-frequency regions. The impedance value is normalized according to the effective electrode area, and the unit is Ω·cm. 2 At least three independent batteries were tested in each group, and the results are expressed as an average, such as... Figure 14 As shown.

[0047] 3. Porosity determination of negative electrode cross section The porosity of the negative electrode cross-section was determined using scanning electron microscopy combined with image binarization. Negative electrodes were collected before and after 800 cycles, respectively, and washed sequentially with deionized water and anhydrous ethanol, then vacuum-dried at 60°C to constant weight. The dried electrodes were cut perpendicular to their surface, fixed to the sample stage with conductive adhesive, and the cross-section was sputter-coated with gold. The electrode cross-section was observed using scanning electron microscopy, and images were acquired under the same accelerating voltage, working distance, magnification, and brightness / contrast conditions. Three independent electrodes were randomly selected from each group, and at least five non-overlapping fields of view were acquired for each electrode.

[0048] The obtained cross-sectional images were imported into ImageJ software and uniformly converted to 8-bit grayscale images. Regions without scale bars, annotations, or electrode edge defects were selected as the statistical regions. The same thresholding method was used to binarize and separate the porous and solid phase regions, with the porous region set to black and the solid phase region set to white. Isolated noise points were removed without altering the pore boundaries. Porosity P was calculated using the following formula: P=A P / A t ×100% Among them, A P A is the pixel area of ​​the pore region in the binarized image. t The total pixel area of ​​the statistical region. The porosity of each sample is the average of the test results of all effective fields of view, and is expressed as mean ± standard deviation. Samples before and after the cycle were prepared using the same sample preparation method, imaging parameters, statistical region selection principles, and image processing parameters to ensure the comparability of the test results. The results are as follows: Figure 15 As shown.

[0049] Figure 4 The figures show the hydrogen evolution reaction current density and maximum current density of Examples 2, 2, and 3 at the same potential. Red represents Comparative Example 2, black represents Comparative Example 3, and blue represents Example 2. The hydrogen evolution reaction current density is the current density at -1.2V. The hydrogen evolution reaction current density of Example 2 is -0.10A, that of Comparative Example 2 is -0.045A, and that of Comparative Example 3 is -0.055A. The maximum current density of Example 2 is 0.12A, that of Comparative Example 2 is 0.05A, and that of Comparative Example 3 is 0.03A. The iron-air battery obtained in Example 2 has high activity. The current in the negative potential region includes contributions from the iron reaction and hydrogen evolution. Hydrogen evolution suppression is based on a negative shift of the initial potential.

[0050] Depend on Figure 5 It can be seen that Comparative Example 3 can only cycle 100 times at a 0.5C rate, with a capacity retention of approximately 60%. Comparative Example 2, using a conventional growth method, achieves an improved cycle life of 400 cycles and a capacity retention of 73% due to the formation of a heterojunction. Furthermore, the anode material obtained using the method in Example 2 further improves its cycle life to 800 cycles and its capacity retention to 89%. This demonstrates that the anode material obtained using the method described in Example 2 of this invention exhibits better stability.

[0051] Depend on Figure 6 , 7 It can be seen that after cycling, the morphology change in Example 2 is relatively small, indicating that the FeOOH content formed during cycling is relatively small. Under the same conditions, the FeOOH content in Comparative Examples 2 and 3 increases, indicating that the negative electrode material of Example 2 has higher stability. Figure 13 As shown, the FeOOH content on the negative electrode surface in Example 2 was 45.5%, in Comparative Example 2 it was 66.8%, and in Comparative Example 3 it was 79.8%.

[0052] Depend on Figure 8 , 9 As can be seen from Example 2, Comparative Example 2, and Comparative Example 3, the impedance increased before and after the cycle. Figure 11 It can be seen that Example 2 increased by 0.11, Comparative Example 2 increased by 0.26, Comparative Example 3 increased by 0.42, while the smallest increase was in the Fe-ZnS anode obtained by the preparation method described in this invention.

[0053] Figure 12 In the diagram, the left side represents Comparative Example 1, and the right side represents Example 1. The first circle is red, circles 2–9 are green, and the tenth circle is blue. The cathode area marked by the blue box indicates that, compared to the Comparative Example, the hydrogen evolution reaction (HER) initiation potential in Example 1 shifted negatively from approximately -0.9V to approximately -1.2V, an overall negative shift of approximately 0.3V. This demonstrates that under the same test conditions, a higher overpotential is required to initiate HER, and hydrogen evolution is effectively suppressed. The peak shape and current response between cycles tend to stabilize in circles 2–10, exhibiting good cycle repeatability.

[0054] Figure 14 In Example 2, Comparative Example 2, and Comparative Example 3, the interface charge transfer impedance before and after 50 cycles was 0.84 Ω·cm, respectively. 2 0.95Ω·cm 2 ; 0.94Ω·cm 2 1.20Ω·cm 2 1.12Ω·cm 2 1.54Ω·cm 2Example 2 shows a very small impedance increase of 13.10%, indicating that this system exhibits the best interface stability during cycling, minimal electrode structure damage, and the weakest charge transport kinetic attenuation. This effectively reduces the charge transfer resistance at the electrode interface while significantly improving interface stability during cycling and mitigating the kinetic performance degradation caused by charge-discharge cycling.

[0055] Figure 15 In Example 2, Comparative Example 2, and Comparative Example 3, the negative electrode porosities before and after 800 cycles were 34.2% and 30.8%, 33.8% and 19.3%, and 33.2% and 11.4%, respectively. After 800 long cycles, the porosity of Example 2 decreased by less than 10%, maintaining a porosity retention rate of 90%, effectively suppressing negative electrode volume expansion, mitigating structural collapse during cycling, and improving battery cycle life.

[0056] Examples 3-20 illustrate the cycle performance of different iron-air batteries obtained by adjusting the negative electrode process parameters. Examples 3-20 all adopt the technical solutions described in Examples 1 and 2, but slight adjustments were made during implementation. The types and parameters of the adjusted variables, as well as the adjusted cycle performance, are shown in the table below:

[0057] Note: In the table, MBT represents 2-mercaptobenzothiazole; SC represents sodium citrate; and DMF represents N,N-dimethylformamide.

[0058] The above descriptions are merely a few embodiments of the present invention and are not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any modifications or variations made by those skilled in the art without departing from the scope of the present invention using the disclosed technical content are equivalent to equivalent implementations and fall within the scope of the technical solution.

Claims

1. A negative electrode material, characterized in that: The negative electrode material is composed of active substances, functional additives, conductive agents and binders in a mass ratio of 6-9:1-3:1-1.5:1-1.5; The active substance is iron or zinc; The functional additive is at least one of zinc sulfide, iron sulfide, and lead sulfide. The conductive agent is at least one of carbon nanotubes, mesophase carbon microspheres, and carbon black. The adhesive is at least one of polyvinylidene fluoride and polytetrafluoroethylene.

2. The negative electrode material according to claim 1, characterized in that, The active substance is iron; The functional additive is zinc sulfide; The conductive agent is carbon nanotubes; The adhesive is polyvinylidene fluoride.

3. The method for preparing the negative electrode material according to claim 1 or 2, characterized in that, Includes the following steps: S1. Preparation of composite powder by ball milling under inert atmosphere: Weigh the active material and functional additives according to the ratio and add them to the ball milling jar. Introduce nitrogen or argon to form an inert protective atmosphere. Ball mill for 6-12 hours to obtain composite powder. S2. Preparation of composite solvent and pulp activation: Prepare composite solvent, wherein the mass ratio of main solvent, interface activator and structure directing agent in composite solvent is 7-8:1.5-2.5:0.5-1.5; The composite powder, conductive agent, and binder obtained in step S1 are added to the composite solvent and stirred for 4-8 hours to construct an in-situ Fe-sulfide covalently bonded heterostructure. S3. Coating, drying, and roll forming: The mixed slurry obtained in step S2 is uniformly coated on the surface of the current collector, dried at 100-150℃ for 4-12 hours, and then rolled to obtain the negative electrode material.

4. The method for preparing the negative electrode material as described in claim 3, characterized in that, The main solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, isopropanol, and cyclohexanone; The interface activator is selected from at least one of ethylenedithiol, 1,3-propanedithiol, thiomalic acid, cysteine, 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, triethylamine, triethanolamine, and ethylenediamine. The structure-directing agent is selected from at least one of hexadecyltrimethylammonium bromide, sodium citrate, and polyacrylic acid.

5. The preparation method according to claim 4, characterized in that: The main solvent is N-methylpyrrolidone or N,N-dimethylformamide; The interface activator is 2-mercaptobenzimidazole or 2-mercaptobenzothiazole; The structure directing agent is hexadecyltrimethylammonium bromide or sodium citrate.

6. The preparation method according to claim 3, characterized in that: The current collector is made of porous nickel foam, nickel foil, graphene-coated nickel foil, 316L stainless steel, or titanium mesh.

7. An iron-air battery, characterized in that, The negative electrode material of the iron-air battery is the negative electrode material according to any one of claims 1-2 or the negative electrode material prepared by the preparation method according to any one of claims 3-6.

8. The iron-air battery according to claim 7, characterized in that, The positive electrode material of the iron-air battery is CoNiO. X / C, Fe-N4 / C or La 0.8 Sr 0.2 CoO3; The electrolyte material of the iron-air battery is KOH, NaOH or LiOH.

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