High tap density iron-manganese material and method for producing the same

Abstract

The application discloses a high tap density iron-manganese material and a preparation method thereof. The iron-manganese material is a composite oxide material containing iron, manganese and oxygen elements, and is composed of crystal face round angle particles. The crystal face round angle particles include a large particle size particle group and a small particle size particle group, and the small particle size particle group is at least partially embedded in a gap region formed by the adjacent large particle size particle group. Contact positions of the adjacent crystal face round angle particles form a local weak neck connection structure, and an identifiable boundary is reserved between the particles. The particle surface is a low opening dense surface. The material reduces the accumulation gap and tap rebound between the particles through the synergistic effect of the crystal face round angle particles, the interstitial grading, the local weak neck connection and the low opening surface, and the tap density can reach 2.30-3.20 g / cm 3 . The preparation method includes precursor preparation, low supersaturation nucleation, interstitial secondary nucleation, wet state compaction curing and pre-oxidation densification heat treatment.

Description

Technical Field

[0001] This invention relates to the technical field of iron-manganese composite oxide materials, and in particular to a high tap density iron-manganese material and its preparation method. Background Technology

[0002] Iron-manganese composite oxides are a class of transition metal composite oxide materials composed of iron, manganese, and oxygen. Due to their tunable valence structure, good redox activity, low raw material cost, and good environmental adaptability, they can be used in battery materials, catalytic materials, adsorbent materials, oxidizing materials, and functional fillers. In these applications, iron-manganese materials typically require processing such as powder conveying, mixing, compaction, coating, filling, or molding. Therefore, their particle morphology, packing state, tap density, and flowability have a significant impact on subsequent processing performance.

[0003] Existing methods for preparing iron-manganese composite oxide materials typically include co-precipitation, hydrothermal methods, oxidative precipitation, thermal decomposition, and spray pyrolysis. These methods can yield spherical, near-spherical, sheet-like, rod-like, flower-like, porous, or blocky iron-manganese oxide particles. For applications requiring high reactivity, current technologies often favor constructing porous, nanosheet, nanorod, or flower-like structures to increase specific surface area and the number of active sites. However, such loose structures often suffer from large internal pore volumes, significant interparticle bridging, and high powder packing porosity, resulting in low tap density.

[0004] For applications requiring high packing volume or good compaction processability, the conventional approach is to improve particle sphericity, increase particle density, or control particle size distribution. However, simply improving particle sphericity cannot fully solve the problem of insufficient compaction density. If the particle size is too concentrated, many interconnected voids will still form between the particles; if the particles have a sharp, polyhedral structure, edge-to-edge or corner-to-face contact will easily occur between the particles, and bridging voids will easily form during compaction; if density is forcibly increased through high-temperature sintering, hard agglomerates are easily formed, causing the particle boundaries to disappear and resulting in a decrease in powder flowability and dispersibility.

[0005] Therefore, how to further reduce the packing voids between particles, reduce structural springback after tapping, and avoid hard agglomeration caused by excessive sintering while maintaining low porosity on the particle surface and dense particle body are key technical problems that need to be solved in the preparation of high tap density iron-manganese materials. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a high-tap-density iron-manganese material and its preparation method. This iron-manganese material does not simply rely on particle spheroidization or high-temperature sintering to increase tap density. Instead, it achieves a higher tap density through the synergistic configuration of crystallized rounded-corner particles, interstitial gradation, localized weak necking, and a low-aperture dense surface. This reduces the internal pore volume of the particles, decreases the inter-particle voids, and reduces tap rebound.

[0007] A high-tap-density iron-manganese material is disclosed, which is an iron-manganese composite oxide material containing iron, manganese, and oxygen. The iron-manganese composite oxide material is composed of crystallized rounded-corner particles, including large-diameter particle groups and small-diameter particle groups. The large-diameter particle groups have crystallized rounded-corner outer contours, and the small-diameter particle groups are at least partially embedded in the interstitial regions formed by adjacent large-diameter particle groups. The contact areas of adjacent crystallized rounded-corner particles form a locally weakly connected structure, and a identifiable boundary is maintained between adjacent crystallized rounded-corner particles. The surface of the crystallized rounded-corner particles is a low-pore, dense surface. The tap density of the high-tap-density iron-manganese material is 2.30–3.20 g / cm³. 3 .

[0008] In this invention, the low-pore density surface does not refer to a completely pore-free or completely smooth particle surface, but rather to a surface where, under scanning electron microscopy, the surface of the crystallized rounded-corner particles does not exhibit obvious through-holes, continuous groups of open pores, or radially extending loose growth structures. This can be determined by the area ratio of the open pore shadow on the particle surface and the presence of radially extending needle-like, rod-like, or plate-like structures. The area ratio of the open pore shadow refers to the percentage of the total projected area of ​​the identifiable open pore regions on the particle surface in the scanning electron microscope image relative to the total projected area of ​​the particle surface. Preferably, the area ratio of the open pore shadow on the low-pore density surface is no greater than 2.5%.

[0009] In this invention, the crystallized rounded-corner particles differ from ordinary spherical particles and also from sharp polyhedral particles. The crystallized rounded-corner particles retain a certain number of smooth, crystallized surface segments, allowing for the formation of relatively stable contact areas between particles. Simultaneously, adjacent smooth, crystallized surface segments are connected by rounded, blunted edges, reducing the bridging effect caused by sharp corners and enabling particles to roll, slide, and rearrange during compaction. This structure combines the stability of crystallized surface contact with the flowability of rounded-corner particles, which is beneficial for improving the packing density of powder.

[0010] In this invention, small-diameter particle groups are at least partially embedded in the interstitial regions formed by adjacent large-diameter particle groups. The large-diameter particle groups constitute the main packing framework, while the small-diameter particle groups fill the voids between the large-diameter particles, forming a gap-filling gradation structure. Compared to particles of a single diameter, this gap-filling gradation structure reduces the black interconnected voids between particles, lowers the packing porosity, and thus increases the tap density.

[0011] In this invention, a localized weak necking structure is formed at the contact area of ​​adjacent crystallized rounded corner particles, and identifiable boundaries are maintained between adjacent particles. This localized weak necking structure differs from the hard agglomeration structure formed by high-temperature sintering; it exists only at the contact area between adjacent particles and does not completely eliminate particle boundaries. This structure can reduce the loose rebound between particles during compaction, improve packing stability, and simultaneously prevent excessive sintering of particles that leads to decreased flowability.

[0012] In this invention, the surface of the crystallized rounded-corner particles is a low-porosity, dense surface. This low-porosity, dense surface reduces the open pore volume within the particles, preventing the formation of loose external growth structures such as flower-like, plate-like, needle-like, and rod-like structures, thereby improving the actual packing quality of the particles themselves. The low-porosity, dense surface, combined with the interstitial gradation structure, can simultaneously reduce both internal and inter-particle porosity.

[0013] Preferably, the outer contour of the crystallized rounded corner particle includes 3 to 12 crystallized smooth surface segments, and adjacent crystallized smooth surface segments are connected by rounded blunt edges; the cumulative length of the crystallized smooth surface segments accounts for 25% to 70% of the perimeter of the outer contour of a single particle.

[0014] By limiting the particle size as described above, we can prevent it from becoming a perfectly smooth sphere or a polyhedral particle with sharp edges. When the cumulative length of the gently sloping crystallized segments is low, the effective contact between particles is insufficient, resulting in poor packing stability. When the cumulative length of the gently sloping crystallized segments is too high, the particle facet orientation effect is enhanced, easily forming bridging voids. Controlling the cumulative length of the gently sloping crystallized segments between 25% and 70% is beneficial for achieving a balance between contact stability and rearrangement flowability.

[0015] Preferably, the equivalent circular diameter of the large-diameter particle group is 0.60–2.20 μm, the equivalent circular diameter of the small-diameter particle group is 0.10–0.55 μm, and the ratio of the average equivalent circular diameter of the large-diameter particle group to that of the small-diameter particle group is 2.0–6.0:1.

[0016] Based on the above particle size distribution, large-diameter particle groups can form the main packing skeleton, while small-diameter particle groups can enter the interstitial regions formed by large-diameter particles. If the size difference between large-diameter and small-diameter particle groups is too small, it is difficult to form effective interstitial filling; if the size difference is too large, small-diameter particles are prone to forming independent fine powder agglomerates or adhering to the particle surface, and cannot stably fill the interstitial regions.

[0017] Preferably, in the scanning electron microscope image, at least 35% of the particles in the small-diameter particle group are located in the interstitial region formed by adjacent large-diameter particle groups, and every 20 μm 2Within the field of view, the number of black connected void regions surrounded by large-diameter particle groups and not filled by small-diameter particle groups is no more than 8.

[0018] The above limitations further emphasize that the small-diameter particles are not simply mixed with the large-diameter particles, but rather have a clearly defined interstitial filling relationship. This positional relationship is an important feature that distinguishes this invention from ordinary wide-diameter powders.

[0019] Preferably, the width of the local weak neck structure is 0.08 to 0.38 times the equivalent circle diameter of the smaller particle among the adjacent crystallized rounded corner particles; the local weak neck structure is distributed in the point contact, line contact or surface contact area of ​​the adjacent crystallized rounded corner particles.

[0020] If the localized weak neck structure is too small, it will be difficult to reduce the rebound after particle compaction; if the localized weak neck structure is too large, it will easily form hard agglomerates, resulting in unclear particle boundaries and reduced flowability. Controlling the width of the localized weak neck structure within the above range is beneficial to achieving a balance between compaction density and powder flowability.

[0021] Preferably, the area ratio of the opening hole shadow of the low-aperture dense surface is not greater than 2.5%; and in the field of view of a scanning electron microscope at 10,000x or higher, the surface of the crystallized rounded corner particles does not have radially extending needle-like, rod-like or plate-like loose growth structures with a length greater than 300 nm.

[0022] This feature effectively distinguishes it from common porous flower-like, nanosheet-like, nanorod-like, or flocculent iron-manganese oxide materials. The low-open-pore, dense surface gives the particles a low open-pore volume, preventing low-density accumulation of powder due to internal pores and external structures during compaction.

[0023] Preferably, the surface of the crystallized rounded corner particles has a layered shallow texture, which extends locally along the particle surface. The width of a single layered shallow texture is 20-120 nm, and the layered shallow texture does not form a through-hole.

[0024] The layered shallow texture reflects the gentle rearrangement process on the particle surface during confined crystal growth and subsequent heat treatment. This shallow texture is not a loose, lamellar external growth structure and does not significantly increase the external porosity of the particles. Instead, it helps to form stable frictional contact between particles and reduces bounce after compaction.

[0025] Preferably, the molar ratio of iron to manganese in the iron-manganese composite oxide material is 0.05–0.60:1; and the BET specific surface area of ​​the high tap density iron-manganese material is 5–45 m². 2 / g, total pore volume is 0.02~0.18cm³ 3 / g, with an angle of repose of 24° to 38°.

[0026] Controlling the ratio of iron to manganese can regulate the precipitation rate, crystal growth behavior, and densification degree of the iron-manganese composite precursor. BET specific surface area and total pore volume constraints can further limit the material from a high-porosity, loose structure to a dense powder structure suitable for high tap density directions.

[0027] A method for preparing a high tap density iron-manganese material includes the following steps: S1. Dissolve iron source salt and manganese source salt in deionized water, add complexing agent and crystal growth regulator, and stir to form iron-manganese mixed precursor solution; S2. While stirring, a precipitant is added dropwise to the iron-manganese mixed precursor solution, and the pH of the system is controlled at 6.4 to 7.2. The total amount of precipitant added is 35% to 55% to form large-diameter crystallized rounded particle nuclei. S3. Reduce the stirring speed, continue to add the remaining precipitant, and raise the pH of the system to 7.6-8.6 to allow small-diameter particles to nucleate and grow in the gap area between large-diameter crystalline rounded particles, thus obtaining iron-manganese composite precipitate slurry. S4. Concentrate the iron-manganese composite precipitate slurry to a solid content of 18% to 35%, and perform wet compaction and curing treatment at 45 to 75°C to form a local weak neck connection structure at the contact part of adjacent particles. S5. The matured product is subjected to solid-liquid separation, washing and drying to obtain an iron-manganese composite intermediate. S6. The iron-manganese composite intermediate is subjected to pre-oxidation and surface treatment in an oxygen-containing atmosphere, followed by medium-temperature densification heat treatment to obtain the high tap density iron-manganese material.

[0028] The preparation method of this invention is not a common one-step coprecipitation and simple heat treatment, but rather a continuous control of particle structure through four key processes: low supersaturation nucleation, interstitial secondary nucleation, wet compaction and ripening, and pre-oxidation densification.

[0029] In step S1, the complexing agent and crystal growth regulator can regulate the release rate of iron and manganese ions, reduce the local supersaturation surge during precipitation, and induce the particles to form a crystallized rounded outer contour. The complexing agent can be one or more of citrate, tartrate, gluconate, and ethylenediaminetetraacetate; the crystal growth regulator can be one or more of polycarboxylate, polyvinylpyrrolidone, polyethylene glycol, and low molecular weight alkanolamine.

[0030] In step S2, a portion of the precipitant is added dropwise within the lower supersaturation range of pH 6.4–7.2, allowing the iron-manganese composite precipitate to slowly nucleate and form large-diameter, rounded-corner crystalline primary nuclei. If the pH is too high or the precipitant is added too quickly during this stage, flocculent fine powder or disordered agglomeration may easily form; if the pH is too low, precipitation will be insufficient, making it difficult to form stable primary nuclei.

[0031] In step S3, after reducing the stirring speed, the remaining precipitant is added dropwise while the pH is increased, causing the system to enter the secondary nucleation and interstitial growth stage. At this point, newly formed small-diameter particles tend to deposit and grow in the local interstitial regions between existing large-diameter particles, thus forming an interstitial gradation structure. This step is an important technological basis for forming small-diameter particle groups embedded in the interstitial regions of large-diameter particle groups.

[0032] In step S4, the slurry is concentrated to a high solids content and then wet-pressed and matured, causing the particles to settle, contact, rearrange, and slightly redeposit in a wet environment. This process can form local weak necking structures at the contact points of adjacent particles, and because the temperature is low and the system is still wet, it will not cause high-temperature hard agglomeration, and identifiable boundaries will still be retained between particles.

[0033] In step S6, the pre-oxidation and surface-fixing treatment can fix the crystal planes and particle boundaries on the particle surface at a lower temperature, reducing structural abrupt changes during subsequent heating. The medium-temperature densification heat treatment can reduce the open pore volume on the particle surface and inside, resulting in a low-open-pore, dense state on the particle surface. By combining pre-oxidation and surface-fixing with medium-temperature densification, severe sintering and boundary disappearance of particles caused by direct high-temperature treatment can be avoided.

[0034] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following aspects: 1. This invention constructs crystallized rounded-corner particles, enabling iron-manganese materials to simultaneously possess crystallographic contact stability and rounded-corner rearrangement capabilities. This avoids the formation of bridging voids in ordinary sharp polyhedral particles during compaction, and also avoids the problem of insufficient contact stability in completely smooth spherical particles.

[0035] 2. This invention constructs a gap-filling gradation structure of large-diameter particle groups and small-diameter particle groups, so that small-diameter particles at least partially enter the gap region formed by adjacent large-diameter particles, significantly reducing the black interconnected voids between particles and improving the packing density of powder.

[0036] 3. The present invention uses a local weak neck connection structure to form a slight connection between adjacent particles at the contact point, which reduces the loose rebound after the compaction process, while the particle boundaries remain identifiable, avoiding high-temperature hard agglomeration that leads to a decrease in powder flowability and dispersibility.

[0037] 4. This invention reduces the internal open pore volume of particles by using a low-pore, dense surface and avoids loose external growth structures such as needle-like, rod-like, sheet-like, or flower-like structures, so that the material can obtain a high tap density while maintaining a good particle morphology.

[0038] 5. The preparation method of the present invention controls particle growth in a synergistic manner through low supersaturation nucleation, interstitial secondary nucleation, wet compaction ripening and pre-oxidation densification heat treatment, which can stably obtain high tap density iron-manganese materials. The process conditions are mild and suitable for scale-up preparation. Attached Figure Description

[0039] Figure 1 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Example 1, with a magnification of 15,000.

[0040] Figure 2 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Example 1, with a magnification of 10,000.

[0041] Figure 3 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Example 1, with a magnification of 5000x.

[0042] Figure 4 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Example 1, with a magnification of 2500x.

[0043] Figure 5 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Example 1, with a magnification of 1000x.

[0044] Figure 6 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Example 1, with a magnification of 500x.

[0045] Figure 7 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Example 2, with a magnification of 15,000.

[0046] Figure 8 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Example 2, with a magnification of 10,000.

[0047] Figure 9 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Example 2, with a magnification of 5000x.

[0048] Figure 10 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Example 2, with a magnification of 2500x.

[0049] Figure 11 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Example 2, with a magnification of 1000x.

[0050] Figure 12 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Example 2, with a magnification of 500x.

[0051] Figure 13 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Comparative Example 1, with a magnification of 30,000.

[0052] Figure 14 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Comparative Example 1, with a magnification of 20,000.

[0053] Figure 15 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Comparative Example 1, with a magnification of 10,000.

[0054] Figure 16 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Comparative Example 1, with a magnification of 5000x.

[0055] Figure 17 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Comparative Example 1, with a magnification of 2000x.

[0056] Figure 18 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Comparative Example 1, with a magnification of 1000x.

[0057] Figure 19 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Comparative Example 2, with a magnification of 30,000.

[0058] Figure 20 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Comparative Example 2, with a magnification of 20,000.

[0059] Figure 21 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Comparative Example 2, with a magnification of 10,000.

[0060] Figure 22 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Comparative Example 2, with a magnification of 5000x.

[0061] Figure 23 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Comparative Example 2, with a magnification of 2000x.

[0062] Figure 24 The image shown is a scanning electron microscope image of the iron-manganese material prepared in Comparative Example 2, with a magnification of 1000x. Detailed Implementation

[0063] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0064] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0065] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0066] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0067] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention.

[0068] Example 1

[0069] This embodiment discloses a method for preparing a high tap density iron-manganese material, including the following steps: S1. Preparation of precursor solution.

[0070] Weigh 9.6 parts by weight of manganese sulfate monohydrate and 2.4 parts by weight of ferric sulfate nonhydrate and add them to 100 parts by weight of deionized water. Stir at 500 rpm for 20 minutes at 25°C until completely dissolved to obtain a mixed solution of iron and manganese salts.

[0071] Add 1.2 parts by weight of sodium citrate, 0.35 parts by weight of sodium tartrate, and 0.18 parts by weight of polyvinylpyrrolidone to the iron-manganese salt mixed solution, and continue stirring for 15 minutes to form an iron-manganese mixed precursor solution. Sodium citrate and sodium tartrate act as complexing agents, and polyvinylpyrrolidone acts as a crystal facet growth regulator.

[0072] S2, low-supersaturation nucleation.

[0073] Ammonium bicarbonate was prepared into a 1.0 mol / L precipitant solution. The iron-manganese mixed precursor solution was heated to 50°C and stirred at 650 rpm. 45% of the total precipitant was added dropwise over 60 minutes, while ammonia was used to adjust the pH of the system to maintain it at 6.8 ± 0.1, thus forming large-diameter, rounded-corner crystal nuclei.

[0074] S3, interstitial secondary nucleation and interstitial growth.

[0075] Reduce the stirring speed to 220 rpm and continue adding the remaining 55% of the precipitant solution dropwise over 90 minutes, while slowly raising the pH of the system to 8.1 ± 0.1. After the addition is complete, continue stirring at the same temperature for 30 minutes to allow the small-diameter particles to nucleate and grow interstitially in the gaps between the large-diameter, rounded-corner crystalline particles, thus obtaining the iron-manganese composite precipitate slurry.

[0076] S4. Wet compaction and curing treatment.

[0077] The iron-manganese composite precipitated slurry was pre-concentrated to a solid content of 26% through natural sedimentation and vacuum filtration. The concentrated slurry was placed in a 60°C water bath, and the stirring was stopped and allowed to stand and compact for 60 minutes. Then, it was stirred at 150 rpm with low shear for 90 minutes to cause wet rearrangement of particles and the formation of local weak necking structures at the contact points of adjacent particles.

[0078] S5. Solid-liquid separation, washing, and drying.

[0079] The wet-pressed and matured slurry was centrifuged at 4000 rpm for 8 minutes. The resulting precipitate was washed three times with deionized water and once with anhydrous ethanol. The washed product was then dried in a vacuum drying oven at 80°C for 12 hours to obtain the iron-manganese complex intermediate.

[0080] S6, pre-oxidation surface treatment and medium-temperature densification heat treatment.

[0081] The iron-manganese composite intermediate was placed in a tube furnace and heated to 220°C at a heating rate of 2°C / min in air atmosphere, and held for 60 minutes for pre-oxidation and surface treatment. Then, it was heated to 460°C at a heating rate of 3°C / min and held for 2 hours for medium-temperature densification heat treatment. After natural cooling to room temperature, high tap density iron-manganese material was obtained.

[0082] The high tap density iron-manganese material prepared in this embodiment has a tap density of 2.80 g / cm³. 3 Scanning electron microscopy revealed that the material consists of crystallized, rounded-corner particles with low porosity and shallow texture on the particle surface. Large-diameter and small-diameter particle groups coexist, with small-diameter particles at least partially embedded in the interstitial regions formed by large-diameter particles. Local weak necking structures are visible at the contact points of adjacent particles, while the particle boundaries are still identifiable.

[0083] The morphological parameters of the material in this embodiment were obtained by statistical analysis of the scanning electron microscope (SEM) images, as shown in Table 1 below. When performing the SEM image analysis, the open aperture shadow area ratio was calculated as the ratio of the sum of the projected areas of the identifiable open aperture regions on the particle surface to the sum of the projected areas of the particle surface being analyzed. Radially extending needle-like, rod-like, or plate-like loose growth structures were confirmed by observation using SEM images at magnifications of 10,000x or higher.

[0084] Table 1 Material morphology parameters of Example 1

[0085] Example 2

[0086] This embodiment discloses a method for preparing a high tap density iron-manganese material, which differs from Embodiment 1 in that: In S1, 10.2 parts by weight of manganese sulfate monohydrate and 1.8 parts by weight of ferric nitrate nonahydrate were weighed and added to 100 parts by weight of deionized water; 0.95 parts by weight of sodium citrate, 0.22 parts by weight of sodium gluconate and 0.12 parts by weight of polyethylene glycol were added to form a mixed iron-manganese precursor solution.

[0087] In S2, the system temperature was controlled at 48℃, the stirring speed was 600 rpm, and 50% of the total amount of precipitant was added dropwise over 70 minutes, while the pH of the system was maintained at 6.9±0.1.

[0088] In S3, the stirring speed was reduced to 200 rpm, and the remaining 50% of the precipitant solution was added dropwise over a period of 100 minutes. At the same time, the pH of the system was slowly increased to 8.0 ± 0.1.

[0089] In S4, the slurry is concentrated to a solid content of 24%, then allowed to stand and compact at 58°C for 50 minutes, and then stirred at 130 rpm with low shear for 100 minutes.

[0090] In S6, the pre-oxidation surface treatment temperature is 210℃, and the holding time is 50 minutes; the medium-temperature densification heat treatment temperature is 440℃, and the holding time is 2 hours.

[0091] The high tap density iron-manganese material prepared in this embodiment has a tap density of 2.50 g / cm³. 3 Scanning electron microscopy revealed that the material is mainly composed of rounded particles with low porosity on the particle surface. The particle size distribution is more concentrated than that of Example 1, and the particles are uniformly packed. However, the proportion of small-diameter particles interspersed and the proportion of local weak necks are lower than those of Example 1.

[0092] The morphological parameters of the material in this embodiment are shown in Table 2 below.

[0093] Table 2 Material morphology parameters of Example 2

[0094] Example 3

[0095] This embodiment discloses a method for preparing a high tap density iron-manganese material, which differs from Embodiment 1 in that: In S1, the amount of manganese sulfate monohydrate is 9.0 parts by weight, and the amount of ferric sulfate nonhydrate is 3.0 parts by weight; the complexing agent is 1.0 parts by weight of sodium citrate and 0.30 parts by weight of disodium ethylenediaminetetraacetate, and the crystal growth regulator is 0.15 parts by weight of sodium polycarboxylate.

[0096] In S2, the pH of the system is controlled at 6.7±0.1, and 42% of the total amount of precipitant is added dropwise to form large-diameter, rounded-corner crystalline particles as initial nuclei.

[0097] In S3, the pH of the system was raised to 8.3±0.1, and the remaining 58% of the precipitant was added dropwise over a period of 100 minutes.

[0098] In S4, the slurry solid content is 28%, the static compaction time is 80 minutes, and the low-shear shaping time is 80 minutes.

[0099] In S6, the pre-oxidation surface treatment temperature is 230℃, and the holding time is 60 minutes; the medium-temperature densification heat treatment temperature is 480℃, and the holding time is 1.5 hours.

[0100] The high tap density iron-manganese material prepared in this embodiment has a tap density of 2.68 g / cm³. 3 The material has a gap-filling gradation structure formed by large and small particles, with weak necks visible between particles in some areas, and the particle boundaries are still clearly distinguishable.

[0101] Comparative Example 1 This comparative example discloses a method for preparing an iron-manganese material, which differs from Example 1 in that: Instead of performing interstitial secondary nucleation and interstitial growth in step S3, the precipitant is added dropwise in step S2, and the pH of the system is directly adjusted to 8.1±0.1. At the same time, the wet compaction and ripening treatment in step S4 is not performed. After precipitation, solid-liquid separation, washing, drying and heat treatment are performed directly.

[0102] The tap density of the iron-manganese material prepared in this comparative example is 1.70 g / cm³. 3 Scanning electron microscopy revealed that the particles primarily exhibited a truncated polyhedral morphology, with strong independence between particles, indistinct weak necking structures, and numerous unfilled black interconnected voids between larger particles. This structure indicates that simply forming polyhedral particles and low-pore surfaces is insufficient to significantly improve the tap density.

[0103] Comparative Example 2 This comparative example discloses a method for preparing an iron-manganese material, which differs from Example 1 in that: In step S3, after reducing the stirring speed, the precipitant is not slowly added, but the pH is maintained at 7.2 and stirring is continued for 120 minutes. In step S4, the slurry solid content is only 10%, and it is only stirred and matured at 300 rpm for 90 minutes without a static compaction stage.

[0104] The tap density of the iron-manganese material prepared in this comparative example is 1.80 g / cm³. 3 Scanning electron microscopy revealed that the particles were mainly rounded ellipsoids or rounded short columns with low-level pores on the surface. However, the inter-particle size of small particles was insufficient, and there were still many interconnected gaps between the particles. In some areas, there were also agglomerated abnormal aggregates.

[0105] Comparative Example 3 This comparative example discloses a method for preparing an iron-manganese material, which differs from Example 1 in that: In step S4, static compaction and low-shear shaping are not performed; instead, the slurry is directly filtered and dried. In step S6, no pre-oxidation surface treatment is performed; the temperature is directly increased to 600℃ at 8℃ / min and held for 2 hours.

[0106] Although some particles of the iron-manganese material prepared in this comparative example underwent sintering and bonding, the particle boundaries locally disappeared, forming a hard agglomerate structure, increasing the angle of repose, and reducing powder flowability. Its tap density was 2.18 g / cm³. 3 This is lower than that of Examples 1 and 2.

[0107] Performance testing 1. Scanning electron microscopy morphology test.

[0108] The morphology of the iron-manganese materials prepared in Examples 1-3 and Comparative Examples 1-3 was observed using a scanning electron microscope. Before testing, the powder samples were uniformly dispersed on the surface of conductive adhesive and then sputtered with gold. The particle morphology of the materials was observed at magnifications of 500x, 1000x, 2500x, 5000x, 10000x, 15000x, or 30000x.

[0109] The scanning electron microscope images were statistically analyzed using ImageJ or equivalent image analysis software. At least five fields of view were selected for each sample, and at least 100 particles were counted in each field of view. The equivalent circle diameter of the particles, the number of smooth crystallization segments, the cumulative length ratio of smooth crystallization segments, the interstitial ratio of small-diameter particles, the width of local weak necks, and the area ratio of the opening aperture shadow were calculated.

[0110] 2. Tap density test.

[0111] The tapped density was tested according to GB / T 5162-2021 "Determination of Tapped Density of Metal Powders". A certain mass of iron-manganese material powder was weighed and placed in a graduated cylinder, and tapped under specified vibration conditions until the volume change was not obvious. The sample mass and tapped volume were recorded, and the tapped density was calculated. Each sample was tested 3 times, and the average value was taken.

[0112] 3. Specific surface area and pore volume test.

[0113] Specific surface area and total pore volume were measured using a nitrogen adsorption-desorption method. Before testing, the samples were degassed under vacuum at 120°C for 6 hours. Specific surface area was calculated using the BET method, and total pore volume was calculated based on the adsorption capacity at a relative pressure close to 0.99.

[0114] 4. Angle of repose test.

[0115] The angle of repose was tested using the fixed funnel method. The powder sample was allowed to flow naturally from a funnel at a fixed height, forming a conical pile. The height and bottom diameter of the pile were measured, and the angle of repose was calculated. Each sample was tested three times, and the average value was taken.

[0116] The performance test results of the examples and comparative examples are shown in Table 3 below.

[0117] Table 3 Performance Test Results

[0118] As shown in Table 3, all three examples achieved high tap densities. Specifically, Example 1 achieved a tap density of 2.80 g / cm³ through the synergistic effect of crystallized rounded-corner particles, interstitial gradation structure, localized weak necking structure, and low-pore, dense surface. 3 Furthermore, the angle of repose remains at a low level, indicating that it possesses both high packing density and good powder flowability.

[0119] Although Comparative Example 1 formed truncated polyhedral particles and a low-pore surface, it lacked an effective interstitial gradation structure and local weak necking structures, resulting in numerous interconnected voids between particles and a tap density of only 1.70 g / cm³. 3 .

[0120] Although Comparative Example 2 showed improved particle rounding and a lower surface porosity, its tap density was only 1.80 g / cm³ due to insufficient intergranular embedding of small-diameter particles and the lack of a weak necking structure formed by wet compaction and ripening. 3 .

[0121] Comparative Example 3, due to the lack of pre-oxidation surface treatment and excessively high heat treatment temperature, resulted in localized hard agglomeration and the disappearance of particle boundaries. Although its total pore volume was low, its angle of repose was significantly increased, powder flowability decreased, and its tap density did not reach the levels of Examples 1-3.

[0122] The above results show that the high tap density of the present invention does not simply originate from particle rounding, low pore volume or high temperature sintering, but rather from the synergistic effect of crystallized rounded corner particles, interstitial gradation of large and small particles, preservation of local weak necking boundaries and low-pore dense surface.

[0123] The above description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, several improvements and modifications can be made to the above technical solutions without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

[0124] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A high tap density iron-manganese material, characterized in that, This material is an iron-manganese composite oxide material containing iron, manganese, and oxygen elements; The iron-manganese composite oxide material is composed of crystallized rounded corner particles, which include large-diameter particle groups and small-diameter particle groups. The large-diameter particle group has a crystallized rounded outer contour, and the small-diameter particle group is at least partially embedded in the gap region formed by adjacent large-diameter particle groups. The contact area between adjacent crystallized rounded corner particles forms a locally weak necked structure, and a identifiable boundary is retained between adjacent crystallized rounded corner particles; the surface of the crystallized rounded corner particles is a low-pore, dense surface; the tap density of the high-taper-density iron-manganese material is 2.30–3.20 g / cm³. 3 .

2. The high tap density iron-manganese material according to claim 1, characterized in that, The outer contour of the crystallized rounded corner particle includes 3 to 12 crystallized smooth surface segments, and adjacent crystallized smooth surface segments are connected by rounded blunt edges; the cumulative length of the crystallized smooth surface segments accounts for 25% to 70% of the perimeter of the outer contour of a single particle.

3. The high tap density iron-manganese material according to claim 1, characterized in that, The equivalent circular diameter of the large-diameter particle group is 0.60–2.20 μm, the equivalent circular diameter of the small-diameter particle group is 0.10–0.55 μm, and the ratio of the average equivalent circular diameter of the large-diameter particle group to that of the small-diameter particle group is 2.0–6.0:

1.

4. The high tap density iron-manganese material according to claim 1, characterized in that, In scanning electron microscope images, at least 35% of the particles in the small-diameter particle group are located in the interstitial region formed by adjacent large-diameter particle groups, and every 20 μm 2 Within the field of view, the number of black connected void regions surrounded by large-diameter particle groups and not filled by small-diameter particle groups is no more than 8.

5. The high tap density iron-manganese material according to claim 1, characterized in that, The width of the local weak neck structure is 0.08 to 0.38 times the equivalent circle diameter of the smaller particle among the adjacent crystallized rounded corner particles; the local weak neck structure is distributed in the point contact, line contact or surface contact area of ​​the adjacent crystallized rounded corner particles.

6. The high tap density iron-manganese material according to claim 1, characterized in that, The area ratio of the opening hole shadow of the low-aperture dense surface is no greater than 2.5%; in the field of view of a scanning electron microscope at 10,000x or higher, there are no radially extending needle-like, rod-like or plate-like loose growth structures with a length greater than 300 nm on the surface of the crystallized rounded corner particles.

7. The high tap density iron-manganese material according to claim 1, characterized in that, The surface of the crystallized rounded corner particles has a layered shallow texture, which extends locally along the particle surface. The width of a single layered shallow texture is 20-120 nm, and the layered shallow texture does not form a through-hole.

8. The high tap density iron-manganese material according to claim 1, characterized in that, The molar ratio of iron to manganese in the iron-manganese composite oxide material is 0.05–0.60:1; the BET specific surface area of ​​the high tap density iron-manganese material is 5–45 m². 2 / g, total pore volume is 0.02~0.18cm³ 3 / g, with an angle of repose of 24° to 38°.

9. A method for preparing a high tap density iron-manganese material according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Dissolve iron source salt and manganese source salt in deionized water, add complexing agent and crystal growth regulator, and stir to form iron-manganese mixed precursor solution; S2. While stirring, a precipitant is added dropwise to the iron-manganese mixed precursor solution, and the pH of the system is controlled at 6.4 to 7.

2. The total amount of precipitant added is 35% to 55% to form large-diameter crystallized rounded particle nuclei. S3. Reduce the stirring speed, continue to add the remaining precipitant, and raise the pH of the system to 7.6-8.6 to allow small-diameter particles to nucleate and grow in the gap area between large-diameter crystalline rounded particles, thus obtaining iron-manganese composite precipitate slurry. S4. Concentrate the iron-manganese composite precipitate slurry to a solid content of 18% to 35%, and perform wet compaction and curing treatment at 45 to 75°C to form a local weak neck connection structure at the contact part of adjacent particles. S5. The matured product is subjected to solid-liquid separation, washing and drying to obtain an iron-manganese composite intermediate. S6. The iron-manganese composite intermediate is subjected to pre-oxidation and surface treatment in an oxygen-containing atmosphere, followed by medium-temperature densification heat treatment to obtain the high tap density iron-manganese material.

10. The method for preparing high tap density iron-manganese material according to claim 9, characterized in that, The wet compaction and curing treatment in step S4 includes a static compaction stage and a low-shear shaping stage. The static compaction stage involves stopping stirring or processing at a speed not exceeding 80 rpm for 30 to 120 minutes. The low-shear shaping stage involves processing at a speed of 100 to 250 rpm for 40 to 180 minutes. In step S6, the temperature of the pre-oxidation surface treatment is 180 to 260°C, and the holding time is 20 to 90 minutes. The temperature of the medium-temperature densification heat treatment is 360 to 560°C, and the holding time is 1 to 4 hours.

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