Synthesis method of single crystal trimanganese tetraoxide, positive electrode material, battery and electrical equipment

Abstract

This invention provides a method for synthesizing single-crystal manganese tetroxide, a cathode material, a battery, and electrical equipment, relating to the field of lithium battery technology. The synthesis method involves solid-state treatment of manganese tetroxide raw material, including: heating the manganese tetroxide raw material during a multi-stage gradient heating process; and using an inert atmosphere and an oxygen-containing atmosphere at different stages of the multi-stage gradient heating to obtain single-crystal manganese tetroxide with a pure cubic spinel phase. This application provides a method for synthesizing single-crystal manganese tetroxide, which induces crystal phase reconstruction through multi-stage gradient heating solid-state treatment under inert and oxygen-containing atmospheres, thereby stably obtaining a pure cubic spinel phase single-crystal material with high structural integrity. This method precisely controls the crystal morphology by controlling the heating rate and atmosphere switching in stages, forming a truncated (111) plane, and the process is simple and requires no chemical additives.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more specifically, to a method for synthesizing single-crystal manganese tetroxide, a cathode material, a battery, and electrical equipment. Background Technology

[0002] Manganese tetroxide (Mn3O4) is an important inorganic functional material widely used in catalysis, batteries, magnetic materials, and other technological fields. In lithium-ion battery systems, Mn3O4, as a precursor for manganese-based cathode materials, has attracted significant attention due to its abundant reserves, low cost, and environmental friendliness. With increasingly stringent requirements for battery performance, the structural stability, cycle life, and energy density of materials have become key areas for improvement. Against this backdrop, single-crystal Mn3O4, with its regular crystal structure, few grain boundaries, and low defects, exhibits superior electrochemical stability and processing performance compared to polycrystalline materials, as it is less prone to structural collapse during charge and discharge.

[0003] Single-crystal manganese tetroxide is mainly classified into two phases based on its crystal structure: tetragonal and cubic spinel. Among them, the cubic spinel phase exhibits superior performance in terms of crystal symmetry, Mn-O octahedral configuration, and structural compatibility with the target product, lithium manganese oxide. Furthermore, due to the presence of Mn... 3+ In spinel structures, the (111) crystal plane is mainly enriched, and this plane is the main source of the Jahn-Teller effect and manganese dissolution during electrochemical cycling. By synthesizing an elastic octahedral morphology with flattened edges and truncated (111) planes, the proportion of highly active (111) planes in the precursor can be reduced from the source, thereby significantly suppressing manganese dissolution in the final cathode material during cycling and improving its structural stability and cycle life.

[0004] Meanwhile, the remaining (111) crystal planes of the obtained cubic single-crystal precursor maintain a highly consistent atomic arrangement and oxygen close-packing with the (111) planes of lithium manganese oxide material, which is beneficial for maintaining the structural integrity of the crystal during the phase transition. Therefore, from the perspective of crystal chemistry and electrochemical mechanism, single-crystal Mn3O4, which combines cubic phase structural purity with a specific truncated octahedral morphology, is considered the most ideal precursor for constructing high-performance, long-life manganese-based cathode materials, and has extremely high research value and application prospects.

[0005] Currently, the main methods for synthesizing single-crystal Mn3O4 include liquid-phase precipitation-oxidation, high-temperature ball milling solid-state reaction, and thermal decomposition. These methods largely rely on the comprehensive control of raw material ratios, reaction conditions, nucleation induction processes, and heat treatment pathways to achieve particle size control and optimized crystallization behavior. However, these methods generally suffer from problems such as complex processes, high dependence on water resources, poor reaction controllability, large equipment investment, and potential release of polluting gases during heat treatment. Furthermore, these methods primarily focus on adjusting crystal morphology or microstructure, lacking systematic research on the stable control of the product's crystal phase composition.

[0006] It is particularly important to note that in existing preparation methods, the products typically exhibit tetragonal or mixed phases, or insufficient cubic phase content, and the crystal morphology (such as platy, spherical, or irregular polyhedral shapes) is uncontrollable, making it difficult to simultaneously achieve a highly pure cubic spinel phase single-crystal structure with a uniform and regular morphology. Currently, there is a lack of effective techniques for stably preparing single-crystal Mn3O4 with both 100% pure cubic spinel phase and specific functional morphologies (such as truncated octahedrons) under industrially adaptable conditions. Existing methods fail to meet the comprehensive requirements of high-performance lithium-ion battery materials for precursor structural consistency, electrochemical stability, and long-cycle performance in terms of crystal phase control precision, morphological uniformity, and structural integrity. The dual challenge of controlling both crystal phase and morphology has become a significant technical obstacle restricting the performance improvement and large-scale application of manganese-based cathode materials.

[0007] In view of this, the present invention is hereby proposed. Summary of the Invention

[0008] The purpose of this invention is to provide a method for synthesizing single-crystal manganese tetroxide, a cathode material, a battery, and an electrical device.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0010] In a first aspect, this application provides a method for synthesizing single-crystal manganese tetroxide, comprising:

[0011] Solid-state treatment of manganese tetroxide raw material, wherein the solid-state treatment includes:

[0012] The manganese tetroxide raw material is heated in a multi-stage gradient heating process, the multi-stage gradient heating includes at least two heating stages with different heating rates; and, in different stages of the multi-stage gradient heating, an inert atmosphere and an oxygen-containing atmosphere are used respectively.

[0013] Thus, a single crystal of manganese tetroxide with pure cubic spinel phase is obtained; wherein the single crystal of manganese tetroxide is in the shape of an octahedron with a truncated (111) facet.

[0014] In a preferred embodiment, the inert atmosphere is argon and / or nitrogen; and / or, the oxygen-containing atmosphere is a mixture of argon and oxygen, a mixture of nitrogen and oxygen, or a mixture of argon, nitrogen, and oxygen; and / or, the manganese tetroxide raw material includes at least one of tetragonal manganese tetroxide, cubic manganese tetroxide, mixed-phase manganese tetroxide, and amorphous manganese tetroxide.

[0015] In a preferred embodiment, during the multi-stage gradient heating process, different atmospheres are switched according to different stages to provide corresponding oxygen partial pressures during the phase transformation and morphology control stages, thereby promoting the transformation of the manganese tetroxide raw material from its original phase to the cubic spinel phase and forming the target octahedral morphology.

[0016] In a preferred embodiment, the multi-stage gradient heating method for solid-state treatment includes:

[0017] In the first stage, the manganese tetroxide raw material is heated to below 1300°C at a heating rate of 10°C / min, and pre-sintered under the protection of the inert atmosphere to initially stabilize the crystal structure.

[0018] In the second stage, the temperature is increased to 1400℃~1500℃ at a heating rate of 5℃ / min and held at that temperature for 1 hour to 3 hours. Under the oxygen-containing atmosphere, the oxygen partial pressure is adjusted to 10. -8 atm~10 -11 atm, to induce phase reconstruction and control the growth of rhombic crystal faces;

[0019] In the third stage, the temperature is increased to no higher than 1560℃ at a heating rate of 15℃ / min and held at that temperature for at least 2 hours, while adjusting the oxygen partial pressure to 10 under the oxygen-containing atmosphere. -11 atm~10 -12 Atm, crystal structure stabilization treatment is performed, and the final morphology is optimized to achieve the flattening of the cubic prism and the truncation of the (111) face.

[0020] In a preferred embodiment, the method for synthesizing single-crystal manganese tetroxide further includes:

[0021] The product obtained by solid-state treatment through the multi-stage gradient heating method is subjected to at least one high-temperature solid-state treatment to obtain the single-crystal manganese tetroxide with a full width at half maximum of 0.25° for the main peak of X-ray diffraction and a regular elastic octahedral morphology.

[0022] Secondly, this application provides a method for preparing a manganese-based cathode material, comprising:

[0023] The pure cubic spinel phase single crystal manganese tetroxide obtained by the synthesis method of single crystal manganese tetroxide as described in the above embodiments is mixed with a lithium source and then sintered at high temperature to obtain a manganese-based cathode material.

[0024] Thirdly, this application provides a manganese-based cathode material, which is prepared by the method for preparing manganese tetroxide cathode material as described in the foregoing embodiments.

[0025] Fourthly, this application provides a battery comprising the manganese-based cathode material as described in the foregoing embodiments.

[0026] Fifthly, this application provides an electrical device including a battery as described in the foregoing embodiments.

[0027] The method for synthesizing single-crystal manganese tetroxide provided in this application achieves precise control over the crystal phase, structural integrity, and microstructure of single-crystal manganese tetroxide by performing solid-state treatment on the manganese tetroxide raw material and combining two core control methods: "multi-stage gradient heating" and "staged atmosphere control", thereby obtaining a product with excellent performance.

[0028] First, a multi-stage gradient heating approach, comprising at least two heating stages with different heating rates, enables precise management of the solid-state reaction process. Unlike traditional uniform or single-step rapid heating, this method allows for setting the optimal heating rate based on the physicochemical changes of the material in different temperature ranges (such as particle pre-sintering, phase transformation, and crystal reconstruction). A faster heating rate in the initial stage promotes particle densification, providing a good microstructure foundation for subsequent reactions; while a slower heating rate in the critical phase transformation temperature range facilitates sufficient atomic diffusion and lattice rearrangement, ensuring a thorough and uniform transformation of the crystal phase to the target cubic phase. This refined heat treatment path effectively avoids uneven grain growth, stress concentration, and structural defects caused by sudden temperature changes, significantly improving the crystal phase purity and structural integrity of the final product.

[0029] Secondly, the combined use of inert and oxygen-containing atmospheres during the multi-stage heating process provides the necessary thermodynamic and kinetic conditions for the stable transformation of the crystal phase. Using an inert atmosphere in the initial heating stage effectively suppresses unnecessary side reactions in the raw materials, maintains the equilibrium of their internal oxidation states, and avoids premature lattice distortion. Subsequently, switching to an oxygen-containing atmosphere during the critical stage of crystal phase reconstruction, by introducing a specific external oxygen partial pressure, actively guides and promotes the ordered rearrangement of lattice oxygen and the construction of a stable Mn-O octahedral structure. This is crucial for ensuring the stable transformation of the crystal structure to a highly symmetric pure cubic spinel phase.

[0030] Through the synergistic effect of the aforementioned heating method and atmosphere control, this method can stably and efficiently convert raw materials in various initial states, such as tetragonal phase, mixed phase, and even amorphous phase, into 100% pure cubic spinel phase single-crystal manganese tetroxide. More importantly, this method can also achieve specific control over the morphology of the product, obtaining an octahedral shape with a truncated (111) facet. According to the background art, the (111) crystal facet is the main cause of subsequent cathode material performance degradation (such as manganese dissolution). Therefore, by truncating this crystal facet and reducing its exposed area, the structural stability and electrochemical cycle life of the material can be improved from the source.

[0031] In summary, this method is simple and requires no additional chemical additives. By relying solely on precise control of the physical process, it can stably obtain single-crystal manganese tetroxide with high crystalline phase purity, high structural integrity, and specific functional morphology, providing an ideal precursor for the preparation of high-performance, long-life manganese-based cathode materials. Attached Figure Description

[0032] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the diffraction rings of the final product, manganese tetroxide, in Example 1 of this application;

[0034] Figure 2 This is a morphology diagram of the final product, manganese tetroxide, in Example 1 of this application;

[0035] Figure 3 This is a morphology diagram of lithium manganese oxide synthesized from single-crystal manganese tetroxide in Example 1 of this application;

[0036] Figure 4 This is a TEM image of the surface of lithium manganese oxide synthesized from single-crystal manganese tetroxide in Example 1 of this application after 50 cycles at high temperature;

[0037] Figure 5 This is a TEM image of the surface of lithium manganese oxide synthesized from single-crystal manganese tetroxide in Comparative Example 1 of this application after 50 cycles at high temperature. Detailed Implementation

[0038] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0039] This application provides a method for synthesizing single-crystal manganese tetroxide, comprising:

[0040] Solid-state treatment of manganese tetroxide raw material, wherein the solid-state treatment includes:

[0041] The manganese tetroxide raw material is heated in a multi-stage gradient heating process, the multi-stage gradient heating includes at least two heating stages with different heating rates; and, in different stages of the multi-stage gradient heating, an inert atmosphere and an oxygen-containing atmosphere are used respectively, so as to obtain a single crystal of pure cubic spinel phase manganese tetroxide; wherein the single crystal manganese tetroxide is in the shape of an octahedron with a truncated (111) facet.

[0042] The aforementioned "raw material" refers to manganese tetroxide (Mn3O4) powder that can be used as a precursor, without limitation on its morphology or crystal phase. The manganese tetroxide raw material may include, but is not limited to, at least one of tetragonal phase manganese tetroxide, cubic phase manganese tetroxide, mixed phase manganese tetroxide, and amorphous manganese tetroxide, that is, it may be tetragonal phase, cubic phase, amorphous or mixed crystal phase.

[0043] For example, particle size D is measured by a laser particle size analyzer. 50 The micrometer diameter is 3.5 μm, and XRD analysis shows a tetragonal phase as the main peak, indicating high porosity.

[0044] The above description of the atmosphere combination in the treatment process under inert and oxygen-containing atmospheres allows for the introduction of different atmospheres at different stages.

[0045] In some embodiments, the inert atmosphere is argon and / or nitrogen; used for high-temperature protection to prevent unnecessary oxidation or phase change.

[0046] In other embodiments, the oxygen-containing atmosphere is a mixture of argon and oxygen, a mixture of nitrogen and oxygen, or a mixture of argon, nitrogen, and oxygen; used to adjust the oxygen partial pressure and guide crystal phase reconstruction.

[0047] In this embodiment, a tube furnace or box furnace with controllable atmosphere can be used; high-purity gas is introduced during the processing, and the gas is precisely proportioned using a mass flow controller; the oxygen partial pressure is adjusted by controlling the ratio of O2 to inert gas. An oxygen partial pressure control system (such as an oxygen sensor) can be configured for dynamic feedback adjustment.

[0048] The aforementioned "solid-state treatment based on multi-stage gradient heating" refers to a heating process that is not completed in one go, but rather in stages, at different rates, and in different temperature zones, with each stage having a different purpose. For example, it can include two different and gradient heating stages, or it can include three heating stages, such as:

[0049] (1) Initial heating stage: particle pre-sintering;

[0050] (2) Intermediate temperature stage: Inducing crystal phase transformation;

[0051] (3) High temperature stage: crystal reconstruction and densification.

[0052] In the above-mentioned further definition of the temperature control method in the multi-stage gradient heating process, the multi-stage gradient heating includes at least two heating stages with different heating rates, which aims to achieve precise control over the sintering behavior of the raw materials and the crystal phase transformation process.

[0053] This temperature control method primarily achieves phased temperature management by setting varying heating rates over different time periods. For example, a relatively fast heating rate can be used in the initial stage to quickly enter the reaction temperature zone, promoting pre-sintering of particles and increasing packing density. In the critical temperature zone of phase transformation, the heating rate can be reduced to prolong the time the material remains in that temperature range, facilitating the full completion of lattice rearrangement and phase transformation kinetics. This gradient heating path facilitates the induction and stabilization of the target crystalline phase while maintaining grain uniformity.

[0054] In practice, this multi-stage heating process can be achieved through a programmable temperature control system. The heating rate and temperature range of different stages can be adjusted according to the state of the raw materials and the capacity of the equipment. The key point is to achieve the ordered evolution of the crystal structure at different heat treatment stages by adjusting the heating rate and combining it with suitable atmospheric conditions.

[0055] In summary, employing a multi-stage heating method with at least two different heating rates facilitates finer structural control during solid-state reactions. Setting a faster heating rate in the initial stage effectively increases the powder's packing density and reduces porosity, providing a sound microstructure foundation for subsequent phase transformation. Conversely, using a slower heating rate in the target phase formation temperature range extends the duration of crystal reconstruction, enhances lattice ordering, and thus strengthens the controllability and stability of cubic phase formation. Furthermore, this heating path design avoids lattice stress concentration and structural distortion caused by rapid temperature changes, reduces crystal defect formation, and improves the structural integrity of the final product. This method also exhibits strong process adaptability; by flexibly setting the heating stages and rate parameters, it can be adapted to different raw materials or equipment conditions, ensuring the stability and consistency of phase control. Therefore, segmented control of the heating rate not only guarantees phase purity but also provides strong assurance for process stability and material properties.

[0056] The aforementioned "gradient heating" differs from uniform heating, representing a change in the heating rate. Specifically, the temperature curve can be set through a programmable temperature-controlled furnace; the stage temperature zones can be determined by combining thermogravimetric analysis (TGA) preliminary experiments; different heating rates are maintained in each stage, and the holding time can be set in each stage.

[0057] In the solid-state treatment process, no liquid phase is involved and no solvent is introduced; the crystal phase transformation occurs simultaneously with particle sintering and rearrangement; the crystal formation kinetics are controlled by temperature.

[0058] The solid-state treatment performed using the aforementioned multi-stage gradient heating method aims to "induce crystal phase reconstruction," which refers to transforming the original crystal phase (such as tetragonal or miscible phase) into a cubic spinel phase through atmosphere and heat treatment conditions. The essence of the crystal phase reconstruction process is the rearrangement of atomic positions; the torsion and symmetry enhancement of the Mn-O octahedron; and the evolution of the structure from distortion to regular symmetry.

[0059] The principle is that phase transformation is influenced by the thermodynamic stability of the crystal and the partial pressure of oxygen. Under suitable temperature and oxygen partial pressure combinations, the cubic phase is the most stable structure. The expression for the octahedral distortion Δ (used to evaluate crystal structure symmetry):

[0060] ;

[0061] in, Represents the length of a single Mn-O bond; This represents the average Mn-O bond length. n represents the number of bonds (usually 6).

[0062] It can be seen that the Δ for the cubic phase is approximately 0, while the Δ for the tetragonal phase is larger, as shown in Table 1 below:

[0063] Table 1. Differences in Crystal Structure Matching

[0064]

[0065] The above-mentioned "obtaining a single crystal of manganese tetroxide with pure cubic spinel phase" means that the crystal phase is cubic (Fd-3m) with high purity (>99%); the structure is single crystal, that is, the final product of manganese tetroxide with no grain boundaries and consistent orientation.

[0066] The detection methods that can be used include X-ray diffraction (XRD) to determine whether it is a single cubic phase (main peak matching); a full width at half maximum (FWHM) of less than 0.25° is used as a standard to indicate high crystal quality; and electron microscopy (such as TEM, SAED) is used to verify whether it is a single crystal.

[0067] A single crystal of pure cubic spinel phase manganese tetroxide was obtained, with regular Mn-O octahedral arrangement; its crystal symmetry is high; it matches LiMn2O4 in the (111) crystal plane direction, which is beneficial to the subsequent synthesis of cathode materials.

[0068] In summary, by employing a multi-stage gradient heating method under inert and oxygen-containing atmospheres for solid-state treatment of manganese tetroxide (Mn3O4) raw materials, crystal phase reconstruction can be induced under both thermodynamic and kinetic driving forces, resulting in the stable transformation of the raw materials into high-purity cubic spinel phase single-crystal Mn3O4. This method effectively controls the oxygen vacancy concentration and structural rearrangement pathways within the crystal by segmented control of the heating rate and adjustment of the oxygen partial pressure in the atmosphere, promoting the formation of a highly ordered three-dimensional symmetrical arrangement of Mn-O octahedra and significantly reducing structural distortion. The obtained single-crystal product exhibits consistent space group and cell parameters close to those of Mn3O4 cathode materials, providing a crucial crystallographic basis for the subsequent construction of manganese-based cathode materials with good interface matching and excellent structural stability.

[0069] In some embodiments, during the multi-stage gradient heating process, different atmospheres are switched according to different stages to provide corresponding oxygen partial pressures during the phase transformation and morphology control stages, thereby promoting the transformation of the manganese tetroxide raw material from its original phase to the cubic spinel phase and forming the target octahedral morphology.

[0070] This embodiment further defines the atmosphere control method, explicitly proposing to switch different atmospheres according to different heating stages during the multi-stage gradient heating process in order to adjust the oxygen partial pressure during the crystal phase transformation stage. The core of this technical feature is that different heating stages have different requirements for the atmosphere environment. Especially in the critical temperature range where crystal phase reconstruction occurs, introducing a suitable oxygen partial pressure can induce and stabilize the formation of the target crystal phase, that is, the transformation from the original crystal phase to the cubic spinel phase and the formation of the target octahedral morphology.

[0071] For example, the initial heating phase can be carried out under an inert atmosphere (such as argon or nitrogen) to suppress the oxidation rate of the raw materials and the formation of unstable phases. After entering the crystal phase transformation stage, the atmosphere is switched to an oxygen-containing atmosphere (such as an argon / oxygen or nitrogen / oxygen mixture) to provide the necessary oxygen partial pressure, promoting the ordered arrangement of Mn-O octahedra and the stable reconstruction of the cubic phase crystal structure. Atmosphere switching can be achieved through a mass flow controller, dynamically adjusted in conjunction with the heating program to match the atmosphere environment with the temperature path.

[0072] Implementing atmosphere switching during multi-stage heating can provide more suitable redox conditions for different reaction stages, facilitating precise control of the crystal phase evolution path. By providing an appropriate oxygen partial pressure environment in the critical temperature range of phase transformation, the oxygen positions and manganese chemical valence states in the crystal can be stabilized, reducing the tendency for non-target crystalline phases to form and enhancing the selectivity and stability of cubic phase formation. Furthermore, this method can improve the repeatability and consistency of the crystal phase transformation, reduce structural inhomogeneities caused by fluctuations in oxygen partial pressure, thereby improving the purity and consistency of the final product's crystal structure. Staged atmosphere switching provides an effective means for the stable evolution of multi-phase systems into a single crystalline phase and is one of the key control measures for achieving high-purity cubic spinel phase single-crystal manganese tetroxide.

[0073] In some embodiments, the multi-stage gradient heating method for solid-state treatment includes:

[0074] (1) In the first stage, the manganese tetroxide raw material is heated to below 1300°C at a heating rate of 10°C / min and pre-sintered under the protection of the inert atmosphere to initially stabilize the crystal structure.

[0075] In the first stage, the manganese tetroxide raw material is heated to below 1300°C at a heating rate of 10°C / min and processed under an inert atmosphere (such as argon or nitrogen).

[0076] This stage mainly aims to achieve the pre-sintering of materials to initially stabilize the crystal structure. That is, by rapidly heating, local sintering is induced on the particle surface to increase the packing density and reduce the porosity, providing a stable particle morphology basis for subsequent crystal phase reconstruction, while preventing unnecessary crystal oxidation due to excessive oxygen partial pressure in the early stage of heating.

[0077] (2) In the second stage, the temperature is raised to 1400℃~1500℃ at a heating rate of 5℃ / min and held for 1 hour~3 hours. Under the oxygen-containing atmosphere, the oxygen partial pressure is adjusted to 10. -8 atm~10 -11Atm (atm) is used to induce crystal phase reconstruction and control the growth of rhombic crystal faces; the temperature can be raised to, for example, 1400℃, 1410℃, 1420℃, 1430℃, 1450℃, 1460℃, 1480℃, 1490℃, 1500℃, etc. The holding time can be 1 hour, 2 hours, 3 hours, etc.

[0078] In the second stage, the temperature is further increased to 1400℃~1500℃ at a slower heating rate (5℃ / min) and held for 1 hour~3 hours. During this stage, the atmosphere is switched to an oxygen-containing atmosphere, and the oxygen partial pressure is controlled at 10. -8 atm~10 -11 The low-oxygen environment of ATM induces crystal phase reconstruction and controls the growth of rhombic crystal faces. This stage is the critical period for crystal phase reconstruction. By holding the crystal at a low oxygen partial pressure for a long time, the Mn-O octahedrons in the original manganese tetroxide crystal can be ordered rearranged, thereby realizing the transformation from a tetragonal or mixed phase to a cubic spinel phase. The regulation of oxygen partial pressure plays an important role in stabilizing the oxidation state of Mn, reducing the oxygen vacancy concentration, and promoting the formation of cubic phase nuclei.

[0079] (3) In the third stage, the temperature is increased to no higher than 1560℃ at a heating rate of 15℃ / min, and held at that temperature for at least 2 hours. Under the oxygen-containing atmosphere, the oxygen partial pressure is adjusted to 10. -11 atm~10 -12 atm (for example, it can be 10) -11 atm, 7.5×10 -12 atm, 5×10 -12 atm, 2.5×10 -12 atm, 10 -12 (atm), to perform crystal structure stabilization treatment and final morphology optimization, so as to achieve the flattening of the cubic prism and the truncation of the (111) face.

[0080] In the third stage, the temperature is further increased to no higher than 1560℃, with the heating rate increased to 15℃ / min, and held at that temperature for at least 2 hours, also in an oxygen-containing atmosphere. The main function of this stage is to further promote crystal growth and densification, and to eliminate residual oxygen vacancies through high-temperature short-time treatment, stabilize the cubic phase crystal structure, and optimize the final morphology to achieve the flattening of the cubic prism and the truncation of the (111) facet. The setting of this stage can effectively improve the crystallinity of the material, reduce the lattice defect density, and enable the final product to have higher structural stability and crystal phase purity.

[0081] Overall, this embodiment achieves precise control over sintering behavior, phase transformation kinetics, and crystal stability by clearly defining the heating stages, controlling the rate of temperature change, and setting the holding time and atmosphere conditions. This provides a clear and feasible operational path for obtaining high-quality, pure cubic spinel phase single-crystal manganese tetroxide.

[0082] In some embodiments, the method for synthesizing single-crystal manganese tetroxide further includes:

[0083] The product obtained by solid-state treatment through the multi-stage gradient heating method is subjected to at least one high-temperature solid-state treatment to obtain the single-crystal manganese tetroxide with a full width at half maximum of 0.25° for the main peak of X-ray diffraction and a regular elastic octahedral morphology.

[0084] The "high-temperature solid-phase treatment" in this step refers to continuing to heat the solid product obtained in the previous stage without introducing liquid phase or chemical reagents.

[0085] This treatment is typically carried out at temperatures higher than the initial sintering stage, and is considered a "post-treatment" stage after the material structure has been largely formed. Its purpose is to further optimize and refine the crystal structure. Through this step, without damaging the existing crystal phase configuration, lattice rearrangement, defect healing, and internal stress release can be further promoted, thereby improving the crystallinity and structural integrity of the material.

[0086] The aforementioned requirement of "at least once" provides flexibility for actual process operation. This treatment can be performed by heating to the target temperature once and holding it for a period of time, or it can be repeated multiple times in stages at different temperature zones. Regardless of the operational path adopted, the core of this step lies in utilizing the thermally driven crystal rearrangement mechanism to further enhance the stability of the crystal structure and the integrity of the single crystal, providing structural assurance for obtaining cubic spinel phase single-crystal Mn3O4 with superior performance.

[0087] It should be noted that the final quality of single-crystal manganese tetroxide is affected by factors such as crystal defects, oxygen vacancies, and structural distortion. Additional high-temperature treatment on top of the initial solid-state treatment helps to further eliminate crystal defects, reduce the half-width at half maximum (FWHM) of the main X-ray diffraction peak (XRD FWHM), achieving the standard of FWHM ≤ 0.25°, and improving the integrity of the single crystal. For example, in the embodiment, after three single-crystallization heat treatments, the FWHM of the (101) plane decreased to 0.048°, significantly better than the sample obtained with only one treatment.

[0088] Therefore, this step embodies an extended heat treatment optimization path, which achieves further control over the crystal microstructure through repeated heat treatment, making the product closer to the ideal single crystal standard.

[0089] This application provides a method for preparing a manganese-based cathode material, comprising: mixing pure cubic spinel phase single-crystal manganese tetroxide obtained by the aforementioned single-crystal manganese tetroxide synthesis method with a lithium source and then subjecting the mixture to high-temperature sintering to obtain the manganese-based cathode material.

[0090] Based on the obtained pure cubic spinel phase single crystal manganese tetroxide, further steps are provided for its application in the preparation of manganese-based cathode materials.

[0091] In the above mixing stage, the obtained single-crystal manganese tetroxide is mixed with a lithium source compound in a set ratio. Further ball milling can then be performed.

[0092] Then, the sintering stage is carried out, in which the above mixture is subjected to high-temperature sintering treatment to obtain manganese-based cathode material.

[0093] In this method, manganese tetroxide is used as a precursor. After mixing with a lithium source (such as lithium carbonate or lithium hydroxide) and undergoing high-temperature treatment, lithium manganese oxide cathode materials, such as spinel-structured materials like LiMn2O4, can be formed. This process belongs to a typical solid-state synthesis route, that is, the target lithium manganese oxide crystal structure is constructed by solid-state diffusion and reaction between the precursor and the lithium source at high temperature.

[0094] The "manganese-based cathode material" is not limited to a specific type. Depending on the sintering conditions and the lithium source ratio, different structural types of lithium manganese oxide materials can be generated, which are widely used in lithium-ion battery cathode systems.

[0095] In practice, the method can be implemented by ball milling or other mechanical mixing methods to fully mix the raw materials, and then sintering them in air, oxygen or inert atmosphere at an appropriate temperature (such as 800–900℃) to promote the reaction of lithium ions with the Mn-O structure in manganese tetroxide to form lithium manganese oxide crystals with good electrochemical performance.

[0096] This application provides a manganese-based cathode material, which is prepared by the aforementioned method for preparing manganese tetroxide cathode material.

[0097] The aforementioned cathode material is a manganese-based cathode material. This material is an electrode active material obtained by using pure cubic spinel phase single-crystal manganese tetroxide as a precursor, which is mixed with a lithium source and sintered at high temperature.

[0098] The "manganese-based cathode material" refers to a lithium-ion battery cathode material constructed with manganese as the main valence metal. Its typical representative is lithium manganese oxide (LiMn2O4) or its related derivatives, which has a spinel-type three-dimensional crystal structure and good electrical conductivity and ion diffusion performance. Since cubic phase Mn3O4 and LiMn2O4 have high matching in crystal structure, and the Mn-O octahedra on their (111) crystal plane are arranged with high consistency, the cathode material prepared by using cubic single crystal Mn3O4 as a precursor can effectively reduce phase transformation distortion, reduce grain boundary defects, and improve the structural stability and cycle life of the material.

[0099] Furthermore, the above-mentioned materials are not limited to the specific composition ratio, crystal orientation, or lithium source type of manganese-based cathode materials, but rather cover all lithium manganese oxide material forms obtained through lithiation processes (such as solid-state sintering) of the aforementioned precursors. Their product forms may include, but are not limited to, micron-sized or submicron-sized single-crystal particles, suitable for various forms of lithium battery structures.

[0100] In this application embodiment, a battery is provided, including the aforementioned manganese-based cathode material.

[0101] The battery comprises a manganese-based cathode material prepared using cubic spinel-phase single-crystal manganese tetroxide as a precursor, which exhibits good structural stability and ion diffusion performance. The battery may also include, but is not limited to, a negative electrode, electrolyte, separator, and casing. The negative electrode can be selected from materials such as graphite, silicon-carbon composites, or lithium titanate, used for embedding and releasing lithium ions during charging and discharging; the electrolyte is an organic carbonate solvent system containing lithium salts (such as LiPF6, LiBF4, etc.), providing a medium for lithium ion migration between the positive and negative electrodes; the separator can be a polyolefin microporous membrane or a ceramic composite membrane, used to isolate the positive and negative electrodes and maintain electrochemical stability; the battery structure can be common packaging forms such as pouch, cylindrical, or prismatic. With the above structural configuration, the battery achieves energy output while possessing good cycle life, rate performance, and safety, making it suitable for various applications such as consumer electronics, electric vehicles, and energy storage systems.

[0102] In this embodiment of the application, an electrical device is provided, including the battery as described above.

[0103] The aforementioned electrical equipment can cover a wide range of fields, including but not limited to vehicles such as electric cars, hybrid cars, and electric motorcycles, as well as portable electronic devices such as smartphones, laptops, and tablets. Furthermore, this electrical equipment can also be applied to energy storage systems, such as home energy storage, commercial energy storage, and grid energy storage, to store renewable energy sources such as solar and wind power, thereby achieving efficient energy management and a stable energy supply.

[0104] The present invention will be further illustrated below with specific embodiments. However, it should be understood that these embodiments are merely for the purpose of more detailed illustration and should not be construed as limiting the present invention in any way.

[0105] Table 1. Key process parameters in the examples and comparative examples

[0106]

[0107] In Table 1, "Stage 1" represents the parameters such as the temperature reached in the first stage, the heating rate, and the atmosphere; "Stage 2" represents the parameters such as the temperature reached in the second stage / holding time, the heating rate, the oxygen partial pressure, and the atmosphere; and "Stage 3" represents the parameters such as the temperature reached in the third stage / holding time, the oxygen partial pressure, and the atmosphere.

[0108] Example 1

[0109] In this embodiment, a manganese tetroxide cathode material was prepared.

[0110] Experimental methods:

[0111] (1) First stage: The cubic phase manganese tetroxide (raw material) is heated from room temperature to 1300℃ in an argon atmosphere at a heating rate of 10℃ / min for pre-sintering.

[0112] (2) Second stage: The above materials are subjected to an oxygen partial pressure of 10 -9 In an atmosphere of argon and oxygen at M, the temperature was raised to 1450°C at a heating rate of 5°C / min and held for 3 hours to reconstruct the crystal phase.

[0113] (3) Third stage: The above materials are subjected to an oxygen partial pressure of 10 -11 In an atmosphere of argon and oxygen at M, the temperature was raised to 1550℃ at a heating rate of 15℃ / min and held for 5 hours to stabilize the crystal structure, thus obtaining the final product, manganese tetroxide cathode material.

[0114] Schematic diagram of the diffraction rings of the final product, manganese tetroxide cathode material (reference). Figure 1 The results showed that it was a single-crystal structure. Figure 2 The morphology diagram of the final product, manganese tetroxide, shows that it is an elastic octahedron with a cube-shaped flattened prism and a truncated (111) face. Figure 3 The image shows the morphology of lithium manganese oxide synthesized from single-crystal manganese tetroxide. The top of the lithium manganese oxide is flattened to reduce the area of ​​the (111) surface.

[0115] Example 2

[0116] In this embodiment, a manganese tetroxide cathode material was prepared.

[0117] The experimental method is basically the same as in Example 1, except that: the raw material in the first stage is tetragonal manganese tetroxide, the atmosphere is nitrogen, and the temperature is raised to 1250℃; the atmosphere in the second and third stages is a mixture of nitrogen and oxygen.

[0118] Example 3

[0119] In this embodiment, a manganese tetroxide cathode material was prepared.

[0120] The experimental method is basically the same as in Example 1, except that: the raw material in the first stage is a mixed-phase manganese tetroxide; and the oxygen partial pressure in the second stage is 10. -10 The temperature was raised to 1400℃ using an atm thermometer and held for 2 hours.

[0121] Example 4

[0122] In this embodiment, a manganese tetroxide cathode material was prepared.

[0123] The experimental method is basically the same as in Example 1, except that: the raw material in the first stage is amorphous manganese tetroxide; and the oxygen partial pressure in the third stage is 10. -12 The temperature was raised to 1500℃ and held for 8 hours using an atm thermometer.

[0124] Comparative Example 1

[0125] In this comparative example, a manganese tetroxide cathode material was prepared.

[0126] The experimental method was the traditional manganese sulfate pyrolysis method:

[0127] The manganese sulfate material was calcined in air at a high temperature of 1050℃ to 1300℃ for 15 hours.

[0128] Comparative Example 2

[0129] In this comparative example, a manganese tetroxide cathode material was prepared.

[0130] The experimental method is basically the same as in Example 1, except that the cubic phase manganese tetroxide raw material is directly heated from room temperature to 1550°C at a heating rate of 10°C / min under an argon atmosphere and held at that temperature for 5 hours (skipping the segmented temperature control step).

[0131] Comparative Example 3

[0132] In this comparative example, a manganese tetroxide cathode material was prepared.

[0133] The experimental method was basically the same as in Example 1, except that: in the second stage, the temperature was raised to 1350℃ at a rate of 15℃ / min; in the second and third stages, the oxygen partial pressure was not controlled and the calcination was carried out in air.

[0134] Comparative Example 4

[0135] In this comparative example, a manganese tetroxide cathode material was prepared.

[0136] The experimental method is basically the same as in Example 1, except that the second and third stages are calcined in air.

[0137] Test experiment:

[0138] 1. Testing method:

[0139] (1) The apparent density (《Metal Powder Apparent Density Test》), porosity (BET test) and particle size (laser particle size analyzer, span=(D)) of the samples prepared in the first stage of Examples 1-4 and Comparative Examples 1-3 were tested. 90 -D 10 ) / D 50 The second stage samples were tested for relative density and grain size, and the third stage samples were tested by X-ray diffraction.

[0140] (2) The single-crystal manganese tetroxide samples finally prepared in Examples 1-4 and Comparative Examples 1-3 were mixed with lithium carbonate at a molar ratio of Li:Mn=1.05:1, and then heated to 850°C at a heating rate of 5°C / min in air atmosphere and kept at the temperature for 12h to obtain lithium manganese oxide cathode material.

[0141] (3) Using the lithium manganese oxide materials synthesized from single-crystal manganese tetroxide prepared in Examples 1-4 and Comparative Examples 1-3 as positive electrodes and lithium metal sheets as negative electrodes, CR2032 button cells were assembled in an argon glove box using 1.0 mol / L LiPF6 / EC (ethylene carbonate) + DMC (dimethyl carbonate) + FEC (fluoroethylene carbonate) (EC, DMC and FEC volume ratio 4.5:4.5:1) as electrolyte. The button cells were subjected to constant current charge-discharge cycles at a current density of 0.1C for 1 cycle, and then at a current density of 1C for 100 cycles, with a voltage range of 3V to 4.3V.

[0142] Among them, EC represents ethylene carbonate; DMC represents dimethyl carbonate; and FEC represents fluoroethylene carbonate.

[0143] 2. Test Results:

[0144] A schematic diagram of the diffraction rings of the final product, manganese tetroxide, obtained in Example 1 is shown below. Figure 1 As shown, the results indicate a single-crystal structure.

[0145] TEM images of lithium manganese oxide synthesized from manganese tetroxide, the final product obtained in the examples, after 50 high-temperature cycles are shown in the reference image. Figure 4 As can be seen, the surface particles are free of cracks. The TEM image of lithium manganese oxide synthesized from the final product of manganese tetroxide obtained in the comparative example after 50 cycles at high temperature is shown below. Figure 5 As can be seen, its surface particles have cracks in many places compared to others.

[0146] Table 2. Physicochemical parameters of products at different stages

[0147]

[0148] Table 3. Battery performance evaluation results for the examples and comparative examples.

[0149]

[0150] analyze:

[0151] Referring to the data in Tables 2 and 3, a comparison of the process conditions used in the embodiments and comparative examples shows that the present invention systematically optimizes key parameters such as heat treatment temperature, heating rate, and oxygen partial pressure control through a combined approach of "multi-stage gradient heating + staged atmosphere control + high-temperature solid-state treatment". This method demonstrates significant advantages in material structure control.

[0152] First, the purity and crystal quality of the crystal phase were significantly improved. According to the data in Table 2, all examples achieved a 100% cubic spinel phase structure, while the comparative samples showed obvious impurity phase components (e.g., Comparative Example 1 contained only 28% cubic phase). XRD test results showed that the full width at half maximum (FWHM) of the main peak in the example samples was controlled between 0.048° and 0.060°, significantly narrower than that of the comparative examples (up to 0.25°), indicating that the crystals had higher crystallinity and structural integrity. This was also confirmed by TEM images, namely, the particle surface of the example samples was smooth and dense with no obvious cracks, while the comparative samples had a large number of microcracks and grain boundary defects, indicating that the latter had insufficient structural stability.

[0153] Second, the electrochemical performance is superior across the board. The cathode material prepared in the examples outperforms the comparative example in several key electrochemical indicators, demonstrating stronger potential for practical applications: the initial efficiency reaches 97.8%~98.9%, significantly higher than the comparative example's 89.2%~92.5%, indicating fewer side reactions during the first lithium insertion process; the discharge specific capacity (0.5C) reaches 120.5mAh / g~125.3mAh / g, far exceeding the comparative example (106mAh / g~115mAh / g); the high-temperature cycle life exceeds 1400 cycles (80% capacity retention at 45℃), while the comparative example's shortest cycle life is only 382 cycles, and the longest does not exceed 656 cycles; the recovery rate after being placed at 60℃ is as high as 96%~98.5%, which is better than the comparative example's performance of less than 92% in all cases.

[0154] These results fully demonstrate that the material of the present invention not only has high intrinsic capacity, but also exhibits more stable structure and more controllable electrochemical reaction under long-term use and high-temperature extreme environments.

[0155] Third, proper impurity control results in cleaner and safer materials. The sulfur impurity content in the materials of the examples is as low as 5ppb~12ppb, far lower than the impurity level of up to 1500ppm in the comparative examples (such as Comparative Example 1). Impurity control is of great significance for suppressing side reactions, delaying electrolyte decomposition, and improving battery safety, especially under high-temperature operating environments.

[0156] Fourth, in terms of microstructure, it is more dense and uniform, which is beneficial for electrochemical transport. The material in the example has a higher apparent density (2.85 g / cm³). 3 ~2.98g / cm 3 The lower porosity (24.3%~28.6%) and smaller particle size distribution span (1.63~1.72) reflect a more compact particle arrangement and more uniform particle size. This microstructural feature directly promotes the improvement of lithium-ion diffusion efficiency, enhances electrode mechanical stability, and reduces polarization resistance.

[0157] Furthermore, many common problems were found in the comparative examples. For instance, Comparative Example 1 used a manganese sulfate pyrolysis process, resulting in disordered crystal phases and excessively high sulfur residue. Comparative Examples 2-4 did not use segmented heating or were calcined in air, leading to coarse grains, increased defects, and unstable crystal phase control. These process problems directly resulted in a comprehensive decline in the material's structural quality and electrochemical performance.

[0158] In summary, the embodiments of this application effectively improve the crystal phase purity, structural integrity, and stability of single-crystal manganese tetroxide by using staged temperature control and oxygen partial pressure adjustment, combined with high-temperature post-treatment. The resulting material not only has high crystallinity and low impurity content, but also exhibits superior capacity, cycle life, and high-temperature stability in practical electrochemical applications. In contrast, existing methods (see comparative examples) have significant shortcomings in crystal phase control, impurity removal, and structural stability, and cannot achieve the same level of performance.

[0159] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for synthesizing single-crystal manganese tetroxide, characterized in that, include: Solid-state treatment of manganese tetroxide raw material, wherein the solid-state treatment includes: The manganese tetroxide raw material is heated in a multi-stage gradient heating process, the multi-stage gradient heating including at least two heating stages with different heating rates; and, in different stages of the multi-stage gradient heating, an inert atmosphere and an oxygen-containing atmosphere are used respectively, thereby obtaining a single crystal of pure cubic spinel phase manganese tetroxide; wherein, the single crystal manganese tetroxide is in the shape of an octahedron with a truncated (111) facet; the solid-state treatment by the multi-stage gradient heating method includes: In the first stage, the manganese tetroxide raw material is heated to below 1300°C at a heating rate of 10°C / minute, and pre-sintered under the protection of the inert atmosphere to initially stabilize the crystal structure. In the second stage, the temperature is increased to 1400℃~1500℃ at a heating rate of 5℃ / min and held at that temperature for 1 hour to 3 hours. Under the oxygen-containing atmosphere, the oxygen partial pressure is adjusted to 10. -8 atm~10 -11 atm, to induce phase reconstruction and control the growth of rhombic crystal faces; In the third stage, the temperature is increased to no higher than 1560℃ at a heating rate of 15℃ / min and held at that temperature for at least 2 hours, while adjusting the oxygen partial pressure to 10 under the oxygen-containing atmosphere. -11 atm~10 -12 Atm was used to stabilize the crystal structure and optimize the final morphology in order to flatten the cubic prism and cut off the (111) face.

2. The method for synthesizing single-crystal manganese tetroxide as described in claim 1, characterized in that, The inert atmosphere is argon and / or nitrogen; and / or, The oxygen-containing atmosphere is a mixture of argon and oxygen, a mixture of nitrogen and oxygen, or a mixture of argon, nitrogen, and oxygen; and / or, The manganese tetroxide raw material includes at least one of tetragonal manganese tetroxide, cubic manganese tetroxide, mixed-phase manganese tetroxide, and amorphous manganese tetroxide.

3. The method for synthesizing single-crystal manganese tetroxide as described in claim 1, characterized in that, During the multi-stage gradient heating process, different atmospheres are switched according to different stages to provide the corresponding oxygen partial pressure during the phase transformation and morphology control stages, so as to promote the transformation of the manganese tetroxide raw material from the original phase to the cubic spinel phase and form the target octahedral morphology.

4. The method for synthesizing single-crystal manganese tetroxide as described in claim 1, characterized in that, Also includes: The product obtained by solid-state treatment through the multi-stage gradient heating method is subjected to at least one high-temperature solid-state treatment to obtain the single-crystal manganese tetroxide with a full width at half maximum of 0.25° for the main peak of X-ray diffraction and a regular elastic octahedral morphology.

5. A method for preparing a manganese-based cathode material, characterized in that, include: The pure cubic spinel phase single crystal manganese tetroxide obtained by the synthesis method of single crystal manganese tetroxide as described in any one of claims 1-4 is mixed with a lithium source and then sintered at high temperature to obtain a manganese-based cathode material.

6. A manganese-based cathode material, characterized in that, It is prepared by the method for preparing manganese tetroxide cathode material as described in claim 5.

7. A battery, characterized in that, Including the manganese-based cathode material as described in claim 6.

8. An electrical-related device, characterized in that, Includes the battery as described in claim 7.

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