A trimanganese tetraoxide with a core-shell structure, and a preparation method and application thereof

Abstract

This invention belongs to the field of battery cathode material technology, specifically relating to a core-shell structured manganese tetroxide, its preparation method, and its application. The preparation method of the core-shell structured manganese tetroxide of this invention includes the following steps: (1) adding PEG, ZIF-8, and Zn to a container containing a manganese sulfate solution. 2+ (1) Ammonia solution is introduced into the container and heated to react; (2) After the reaction is completed, the solid and liquid are separated, and the obtained solid is washed and dried to obtain an intermediate product; (3) The intermediate product is calcined to obtain the core-shell structured manganese tetroxide. The core-shell structured manganese tetroxide of the present invention helps to solve the problems of rapid cycle decay, poor rate performance or insufficient compaction density in the sintering preparation process of lithium manganese oxide using manganese tetroxide in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of battery cathode material technology, specifically relating to a core-shell structure of manganese tetroxide, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, as important energy storage devices in modern society, are widely used in portable electronic devices, electric vehicles, and energy storage systems. Lithium manganese oxide (LiMn2O4) has become one of the most promising cathode materials for lithium-ion batteries due to its low cost, environmental friendliness, and high operating voltage. However, lithium manganese oxide faces many challenges in practical applications, such as rapid capacity decay and poor rate performance, which severely limit its large-scale application and further development.

[0003] Studies have shown that the properties of the precursor play a crucial role in the final performance of lithium manganese oxide. Precursors with different crystal structures, morphologies, and particle sizes can lead to significant differences in the electrochemical performance of lithium manganese oxide during synthesis. For example, a manganese tetroxide precursor with a suitable crystal structure and smaller grain size can result in better cycle stability and rate performance of the synthesized lithium manganese oxide. Currently, preparing manganese tetroxide precursors with specific particle sizes and morphologies by controlling reaction conditions is one of the effective ways to improve the performance of lithium manganese oxide. However, in existing lithium manganese oxide preparation technologies, single precursor (manganese tetroxide) modification methods cannot simultaneously achieve crystal morphology control and lattice stability optimization. Therefore, when manganese tetroxide precursors are used in the preparation of lithium manganese oxide, they can negatively impact the cycle stability and rate performance of the resulting lithium manganese oxide.

[0004] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0005] The purpose of this invention is to provide a core-shell structured manganese tetroxide, its preparation method, and its application, in order to help solve or improve the problem that the cycle stability or rate performance of lithium manganese oxide needs to be improved when manganese tetroxide is used in the preparation of lithium manganese oxide in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing manganese tetroxide with a core-shell structure, comprising the following steps: (1) adding PEG, ZIF-8 and Zn to a container containing a manganese sulfate solution. 2+ (1) Ammonia solution is introduced into the container and heated to react; (2) After the reaction is completed, the solid and liquid are separated, and the obtained solid is washed and dried to obtain an intermediate product; (3) The intermediate product is calcined to obtain manganese tetroxide with a core-shell structure.

[0007] Preferably, in step (1), the mass ratio of PEG to ZIF-8 is 3:1; the molar ratio of ammonia in the ammonia solution to manganese in the manganese sulfate solution is 2.0-2.5; the mass ratio of PEG to manganese sulfate in the manganese sulfate solution is 1:(56-62), and Zn 2+ The molar ratio of manganese in the manganese sulfate solution is 0.5%-1.0%; the reaction temperature is 70-80℃; and the reaction time is 2-6h.

[0008] Preferably, in step (1), ammonia water is first introduced at a rate of 0.3-0.5 mL / min; then ammonia water is introduced at a rate of 1.2-1.4 mL / min, and oxygen is introduced at a rate of 1-3 L / min.

[0009] Preferably, in step (3), the calcination temperature is 400-600℃ and the calcination time is 1h; the calcination is carried out in a mixed atmosphere of H2 and N2, and the volume percentage of H2 is 3%-5%.

[0010] The present invention also provides a manganese tetroxide with a core-shell structure, which adopts the following technical solution: a manganese tetroxide with a core-shell structure, wherein the manganese tetroxide with a core-shell structure is prepared by the method described above.

[0011] The present invention also provides a method for preparing lithium manganese oxide, which adopts the following technical solution: A method for preparing lithium manganese oxide includes the following steps: I. Mixing and grinding manganese tetroxide, manganese dioxide, lithium source, low-valence metal M, high-valence metal N and fluoride as described above to obtain a mixed powder; the low-valence metal M has a valence of divalent or trivalent, and the high-valence metal N has a valence of pentavalent or hexavalent; II. Calcining the mixed powder, and after calcination, crushing and sieving to obtain the lithium manganese oxide.

[0012] Preferably, in step I, the mass ratio of manganese tetroxide and manganese dioxide with a core-shell structure is 1:1-3:1; the molar ratio of lithium in the lithium source to manganese in the mixed powder is (1.05-1.2):(1.85-1.98); the molar ratio of the low-valence metal M to the high-valence metal N is (0.01-0.1):(0.01-0.05); and the molar ratio of the low-valence metal M to lithium in the lithium source is (0.01-0.1):(1.05-1.15).

[0013] Preferably, in step II, the calcination includes a first stage of calcination and a second stage of calcination; the temperature of the first stage of calcination is 450-650℃, and the calcination time is 4-8h; the temperature of the second stage of calcination is 700-850℃, and the calcination time is 8-16h.

[0014] Preferably, the low-valence metal M is selected from Mg.2+ Al 3+ Cu 2+ and Cr 2+ At least one of the following; the high-valence metal N is selected from Nb. 5+ V 5+ Cr 6+ Mo 6+ and W 6+ At least one of the following: the fluoride is at least one of lithium fluoride, magnesium fluoride, and aluminum fluoride.

[0015] This invention also provides a lithium manganese oxide, which adopts the following technical solution: a lithium manganese oxide, wherein the lithium manganese oxide is prepared by the method described above; the chemical formula of the lithium manganese oxide is [insert chemical formula here]. Where, 1.05≤a≤1.2, 0.02≤x≤0.10, 0.01≤y≤0.05, 0.05≤z≤0.115.

[0016] Beneficial effects: This invention constructs a three-level regulation mechanism of "morphology-lattice-defect" through a ternary synergistic system, which solves the problems of rapid cycle decay, poor rate performance and insufficient compaction density in the sintering preparation of lithium manganese oxide using manganese tetroxide in the prior art.

[0017] In the preparation method of manganese tetroxide with a core-shell structure of the present invention, PEG and ZIF-8 are used as modifiers to induce the formation of a "spherical core-porous shell" structure of manganese tetroxide, thereby increasing the tap density of manganese tetroxide (the tap density of manganese tetroxide with a core-shell structure of the present invention can be increased to 2.5-2.85 g / cm³). 3 Specific surface area 0.6-0.8 m² 2 / g). Furthermore, in the method for preparing manganese tetroxide with a core-shell structure according to the present invention, heterovalent ion pre-doping is also performed: Zn is introduced into the manganese sulfate solution. 2+ Through the difference in ionic radius (Zn 2+ 0.074nm vs Mn 2+ (0.080nm) induces lattice distortion and inhibits Mn 3+ The Jahn-Teller effect; surface oxygen vacancy engineering: oxygen vacancies can be introduced onto the particle surface through calcination in a mixed H2 / N2 atmosphere, forming Li + A rapid transport channel. The core-shell structure of manganese tetroxide in this invention provides a uniform support for ion doping, heterovalent ions enhance the stability of the core-shell structure, and oxygen vacancies optimize the interfacial electrochemical kinetics. These three factors synergistically enable Li... + The diffusion coefficient is improved.

[0018] This invention uses a mixture of manganese tetroxide and manganese dioxide, which have core-shell structures, to control the particle size distribution of the raw materials, thus helping to improve the compaction problem of the lithium manganese oxide material at the battery end.

[0019] In the preparation method of lithium manganese oxide of the present invention, through bimetallic element doping and anion doping and their synergistic effect, low-valence metal element M (+2 / +3 valence, such as Mg) is doped. 2+ Al 3+ ) Replace part of Mn 3+ This reduces the number of active ions and, through smaller ionic radii, shortens the Mn-O bond length, thereby improving lattice stability; high-valence transition metals N (+5 / +6 valence, such as Nb) 5+ W 6+ ): Increase the average oxidation state of manganese ions (e.g., Mn) 3+ →Mn 4+ This enhances crystal bond energy and suppresses Mn during charging and discharging. 3+ Disproportionation reaction and lattice collapse; through anion doping with element F, F - Doping into the crystal lattice enhances the strength of ionic bonds through strong electronegativity, while compensating for the capacity loss caused by cation doping and improving the discharge specific capacity. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0021] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0022] This invention addresses the problem that the cycle stability or rate performance of lithium manganese oxide needs to be improved when manganese tetroxide is used in the preparation of lithium manganese oxide. It provides a method for preparing manganese tetroxide with a core-shell structure.

[0023] The method for preparing manganese tetroxide with a core-shell structure according to the present invention includes the following steps: (1) adding PEG, ZIF-8 and Zn to a container containing a manganese sulfate solution. 2+ (1) Pass an ammonia solution into the container and heat it to react; (2) After the reaction is completed, separate the solid and liquid, wash and dry the obtained solid to obtain the intermediate product; (3) Calcine the intermediate product to obtain manganese tetroxide with a core-shell structure.

[0024] In the preparation method of manganese tetroxide with a core-shell structure of the present invention, PEG and ZIF-8 are used as modifiers to induce the formation of a "spherical core-porous shell" structure of manganese tetroxide, thereby increasing the tap density of manganese tetroxide (the tap density of manganese tetroxide with a core-shell structure of the present invention can be increased to 2.5-2.85 g / cm³). 3 Specific surface area 0.6-0.8 m² 2 / g). Furthermore, in the method for preparing manganese tetroxide with a core-shell structure according to the present invention, heterovalent ion pre-doping is also performed: Zn is introduced into the manganese sulfate solution. 2+ Through the difference in ionic radius (Zn 2+ 0.074nm vs Mn 2+ (0.080nm) induces lattice distortion and inhibits Mn 3+ The Jahn-Teller effect; surface oxygen vacancy engineering: through calcination (preferably, calcination conditions are: 500°C, 5% H2 / N2 atmosphere treatment), oxygen vacancies can be introduced on the particle surface to form Li. + A rapid transport channel. The core-shell structure of manganese tetroxide in this invention provides a uniform support for ion doping, heterovalent ions enhance the stability of the core-shell structure, and oxygen vacancies optimize the interfacial electrochemical kinetics. These three factors synergistically enable Li... + The diffusion coefficient is improved.

[0025] This invention utilizes a ternary synergistic system (PEG, ZIF-8, and Zn) 2+ The construction of a multi-level regulation mechanism of "morphology-lattice-defect" helps to solve the problems of rapid cycle decay, poor rate performance or insufficient compaction density of lithium manganese oxide prepared by applying manganese tetroxide to the preparation of lithium manganese oxide in the existing technology.

[0026] In a preferred embodiment of the method for preparing manganese tetroxide with a core-shell structure of the present invention, in step (1), the mass ratio of PEG to ZIF-8 is 3:1; the molar ratio of ammonia in ammonia water to manganese in manganese sulfate solution is 2.0-2.5 (e.g., 2.0, 2.1, 2.2, 2.3, 2.4 or 2.5); the mass ratio of PEG to manganese sulfate in manganese sulfate solution is 1:(56-62) (e.g., 1:56, 1:57, 1:58, 1:59, 1:60, 1:61 or 1:62), Zn 2+The molar ratio of PEG to manganese in the manganese sulfate solution is 0.5%-1.0% (e.g., 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%); the reaction temperature is 70-80℃ (e.g., 70℃, 72℃, 74℃, 76℃, 78℃, or 80℃); and the reaction time is 2-6 h (e.g., 2 h, 3 h, 4 h, 5 h, or 6 h). If the mass ratio of PEG to ZIF is too small, it will cause agglomeration, affecting the particle size distribution; if the proportion of PEG is too large, impurities will be generated, reducing purity. If Zn... 2+ If the proportion of Zn used is too small, its optimizing effect cannot be realized, resulting in incomplete growth of the ZIF structure and inability to uniformly coat or dope into the manganese-based support, thus affecting the stability of the composite material; if the proportion of Zn is too small, the optimization effect of Zn will be insufficient, leading to incomplete growth of the ZIF structure and inability to uniformly coat or dope into the manganese-based support, thus affecting the stability of the composite material. 2+ If the proportion of [agent] used is too high, it will disrupt the structural and performance balance of the system, leading to increased lattice distortion and the formation of impurity phases.

[0027] In a preferred embodiment of the method for preparing manganese tetroxide with a core-shell structure of the present invention, in step (1), ammonia water is first introduced at a rate of 0.3-0.5 mL / min (e.g., 0.3 mL / min, 0.4 mL / min or 0.5 mL / min) for 2 hours (no oxygen is introduced during this stage), and then ammonia water is introduced at a rate of 1.2-1.4 mL / min (e.g., 1.2 mL / min, 1.3 mL / min or 1.4 mL / min) for 4 hours, while oxygen is introduced at a rate of 1-3 L / min (e.g., 1 L / min, 2 L / min or 3 L / min). In the initial stage, the slow introduction of ammonia water (0.3-0.5 mL / min) is conducive to the formation of smaller crystal nuclei, laying the foundation for the "core" of the core-shell structure. In the later stage, the ammonia water introduction rate is accelerated (1.2-1.4 mL / min), which can increase the concentration of manganese ions in the reaction system relatively quickly, promote the deposition and growth of manganese ions on the surface of the crystal nuclei, form the "shell" layer, and help to prepare manganese tetroxide with a good core-shell structure.

[0028] In a preferred embodiment of the method for preparing manganese tetroxide with a core-shell structure according to the present invention, in step (3), the calcination temperature is 400-600℃ (e.g., 400℃, 450℃, 500℃, 550℃ or 600℃), and the calcination time is 1h; the calcination is carried out in a mixed atmosphere of H2 and N2, and the volume percentage of H2 is 3%-5% (e.g., 3%, 4% or 5%). If the calcination temperature is too high, oxygen vacancies are excessively healed, resulting in a sharp decrease in their number; if the calcination temperature is too low, the reducing power of H2 at low temperatures is insufficient to effectively break the Mn-O bonds, failing to form a sufficient number of oxygen vacancies on the surface, or even only producing a small number of unstable defects. If the calcination time is too long, excessive reduction leads to the formation of impurity phases; if the calcination time is too short, the reduction reaction is incomplete, resulting in low-quality oxygen vacancies. If the H2 ratio is too high, MnO (low-valence manganese oxide) or even metallic Mn may be generated, destroying the core-shell structure and phase purity of the original Mn3O4; if the H2 ratio is too low, the reduction reaction will be uneven and the vacancy distribution will be scattered.

[0029] The present invention also proposes a core-shell structure of manganese tetroxide, which is prepared by the method described above in the embodiments of the present invention.

[0030] In a preferred embodiment of the manganese tetroxide with a core-shell structure of the present invention, the D of the manganese tetroxide with a core-shell structure 50 =5-8μm, tap density is 2.5-2.85g / cm³ 3 Its specific surface area is 0.6-0.8 m². 2 / g.

[0031] This invention also proposes a method for preparing lithium manganese oxide. The method for preparing lithium manganese oxide according to an embodiment of this invention includes the following steps: I. Mixing and grinding the core-shell structured manganese tetroxide, manganese dioxide, lithium source, low-valence metal M, high-valence metal N and fluoride as described above to obtain a mixed powder; the low-valence metal M has a valence of divalent or trivalent, and the high-valence metal N has a valence of pentavalent or hexavalent; II. Calcining the mixed powder, and after calcination, crushing and sieving to obtain lithium manganese oxide.

[0032] This invention uses a mixture of manganese tetroxide and manganese dioxide, which have core-shell structures, to control the particle size distribution of the raw materials, thus helping to improve the compaction problem of the lithium manganese oxide material at the battery end.

[0033] In the preparation method of lithium manganese oxide of the present invention, through bimetallic element doping and F doping and their synergistic effect, low-valence metal element M (+2 / +3 valence, such as Mg) is used. 2+ Al 3+ ) Replace part of Mn 3+This reduces the number of active ions and, through smaller ionic radii, shortens the Mn-O bond length, thereby improving lattice stability; high-valence transition metals N (+5 / +6 valence, such as Nb) 5+ W 6+ ): Increase the average oxidation state of manganese ions (e.g., Mn) 3+ →Mn 4+ This enhances crystal bond energy and suppresses Mn during charging and discharging. 3+ The disproportionation reaction and lattice collapse are mitigated; by anion doping with element F, F⁻ doping enters the lattice, which enhances the ionic bond strength through strong electronegativity, while compensating for the capacity loss caused by cation doping and improving the discharge specific capacity.

[0034] Preferably, the mixing and grinding method in step I is dry ball milling; the ball milling speed is 600-1000 rpm (e.g., 600 rpm, 700 rpm, 800 rpm, 900 rpm or 1000 rpm), the ball milling time is 1-2 h (1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h or 2 h), and the ball-to-material ratio is (1-1.5):1 (e.g., 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1).

[0035] Preferably, the particle size of manganese dioxide is D. 50 =13-18μm.

[0036] In a preferred embodiment of the method for preparing lithium manganese oxide of the present invention, in step I, the mass ratio of manganese tetroxide and manganese dioxide with a core-shell structure is 1:1-3:1 (e.g., 1:1, 2:1, or 3:1); the molar ratio of lithium in the lithium source to manganese in the mixed powder is (1.05-1.2):(1.85-1.98) (e.g., 1.05:1.85, 1.05:1.98, 1.05:1.9, 1.2:1.85, 1.2:1.98, 1.2:1.89, 1.12:1.85, 1.13:1.98, or 1.09:1.9); the low-valence metal M and the high-valence metal N... The molar ratio is (0.01-0.1):(0.01-0.05) (e.g., 0.01:0.01, 0.01:0.03, 0.01:0.05, 0.05:0.03, 0.1:0.01, 0.1:0.03 or 0.1:0.03); the molar ratio of low-valence metal M to lithium in the lithium source is (0.01-0.1):(1.05-1.15) (e.g., 0.01:1.05, 0.01:1.1, 0.01:1.15, 0.05:1.1, 0.1:1.05, 0.1:1.1, 0.1:1.15 or 0.1:1.05). If the mass ratio of manganese tetroxide to manganese dioxide with a core-shell structure is too high, the rate performance of the prepared lithium manganese oxide will decrease, ion diffusion will be hindered, and excess Mn3O4 may lead to an increase in Mn content in the final product. 3+ The content is too high, while Mn 3+ Its migration ability is weaker than that of Mn 4+ Furthermore, excessive amounts of low-priced Mn will compress Li. + The diffusion channels; if the mass ratio of manganese tetroxide and manganese dioxide with a core-shell structure is too small, the structural stability of the prepared lithium manganese oxide will decrease, lattice oxygen will be easily lost, and high-valence Mn(+4) has strong oxidizing power, which can easily lead to lattice oxygen (O) loss during calcination or cycling. 2- The metal M is oxidized to O2 and escapes, causing lattice collapse. Furthermore, the low-valence metal M inhibits the growth of Mn. 3+ The Jahn-Teller distortion, enhanced lattice oxygen stability by high-valence metallic N, and the combination of the two optimize Li + Diffusion channels and electron conduction networks; both excessively high or low proportions of these components can disrupt this synergistic effect, leading to unstable lattice structure, impaired ion / electron conduction, or impurity phase formation, ultimately significantly reducing the specific capacity, cycle life, and rate performance of lithium manganese oxide.

[0037] In a preferred embodiment of the method for preparing lithium manganese oxide of the present invention, step II includes a first stage of calcination and a second stage of calcination; the temperature of the first stage of calcination is 450-650℃ (e.g., 450℃, 500℃, 550℃, 600℃ or 650℃), and the calcination time is 4-8h (e.g., 4h, 5h, 6h, 7h or 8h); the temperature of the second stage of calcination is 700-850℃ (e.g., 700℃, 750℃, 800℃ or 850℃), and the calcination time is 8-16h (e.g., 8h, 10h, 12h, 14h or 16h). If the temperature of the first stage of calcination is too high, local over-reaction, impurity phase formation, rapid decomposition of the lithium source, and violent reaction with the manganese source to generate non-target phases can easily occur, disrupting the uniformity of the spinel structure. If the temperature of the first stage of calcination is too low, the reaction kinetics are insufficient, the structure is disordered, the solid-phase reaction is difficult to initiate, and the initial framework of the spinel cannot be formed, leading to chaotic lattice growth and excessively high defect density during the second stage of high-temperature calcination. If the first stage of calcination is too long, over-sintering and grain coarsening can easily occur: prolonged medium-temperature calcination can cause abnormal growth of the initially formed grains, resulting in a decrease in specific surface area and Li + A longer diffusion path leads to reduced rate performance; if the first stage of calcination is too short, incomplete reaction and residual intermediate phases can easily occur: the conversion from the precursor to the primary structure of lithium manganese oxide cannot be completed, leaving a large amount of unreacted MnO. x The presence of lithium salts leads to an increase in impurity phases during the second-stage calcination. If the temperature of the second-stage calcination is too high, excessive grain growth occurs, resulting in a sharp drop in specific surface area: the grain size may increase from the micrometer level to tens of micrometers. + The diffusion distance within the grain increases sharply, leading to a deterioration in high-rate performance. If the temperature of the second-stage calcination is too low, insufficient crystallinity and high defect density can easily occur: low temperatures cannot achieve a complete lattice arrangement, resulting in a large number of vacancies, dislocations, and other defects, which can cause problems during Li charging and discharging. + Increased insertion / extraction resistance leads to poor cycle stability. If the second-stage calcination time is too long, over-oxidation and oxygen loss can easily occur: lattice oxygen easily escapes at prolonged high temperatures, forming oxygen vacancies and inducing the transformation of Mn ions to higher valence states (e.g., Mn2). 4+ If the proportion is too high, it will reduce electronic conductivity; if the second stage of calcination time is too short, the composition uniformity will be insufficient: the diffusion of lithium and manganese ions will not reach equilibrium, the local stoichiometric ratio will deviate, and local overcharging / over-discharging will easily occur during charging and discharging, causing side reactions.

[0038] Preferably, the heating rate of the first calcination stage and / or the second calcination stage is 5°C / min.

[0039] In a preferred embodiment of the method for preparing lithium manganese oxide of the present invention, the low-valence metal M is selected from Mg. 2+ Al 3+Cu 2+ and Cr 2+ At least one of the following; the high-valence metal N is selected from Nb. 5+ V 5+ Cr 6+ Mo 6+ and W 6+ At least one of the following; the fluoride is at least one of lithium fluoride, magnesium fluoride, calcium fluoride, aluminum fluoride, and silicon tetrafluoride.

[0040] This invention also provides lithium manganese oxide, which is prepared using the method described above; the chemical formula of lithium manganese oxide is Li. a Mn 2-x-y M x N y O 4-z F z Where, 1.05≤a≤1.2, 0.02≤x≤0.10, 0.01≤y≤0.05, 0.05≤z≤0.115.

[0041] The following detailed description of the core-shell structured manganese tetroxide, its preparation method, and its application, through specific embodiments, illustrates the present invention.

[0042] Unless otherwise specified, all reagents used in the following examples are commercially available; the main reagents were sourced from: manganese sulfate (purchased from Guizhou Dalong Huicheng); PEG, ammonia, and... Purchased from Aladdin; ZIF-8 purchased from Maclean's; manganese dioxide purity is 92% (mass percentage).

[0043] Example 1 The method for preparing manganese tetroxide with a core-shell structure in this embodiment includes the following steps: (1) Add PEG (3.2 g / L), ZIF-8 (1.07 g / L, particle size 50-100 nm) and Zn to a container (50 L reactor) containing manganese sulfate solution (1.2 mol / L). 2+ (The molar ratio with manganese sulfate is 0.8%), 360 mL of a 2.0 mol / L ammonia solution is introduced into the container (the flow rate of the ammonia solution is 0.4 mL / min for the first 2 hours; the flow rate of the ammonia solution is 1.3 mL / min for the next 4 hours, and oxygen is introduced at a flow rate of 2 L / min when the flow rate of the ammonia solution is 1.3 mL / min), and the mixture is heated to 75 °C and reacted for 6 hours; (2) After the reaction is complete, the solid and liquid are separated, and the obtained solid is washed and dried to obtain the intermediate product; (3) The intermediate product is calcined (in a mixed atmosphere of H2 and N2 with a volume percentage of 5% H2, and kept at 500°C for 1 hour) to obtain manganese tetroxide with a core-shell structure in this embodiment.

[0044] The core-shell structured manganese tetroxide obtained above is applied to the preparation of lithium manganese oxide. The preparation method of lithium manganese oxide in this embodiment includes the following steps: I. 134.2g of manganese tetroxide (D50=6-7μm) with a core-shell structure (calculated based on a battery-grade manganese tetroxide purity of 99.3%-99.5%; the molar number of manganese tetroxide with a core-shell structure is calculated based on the relative molecular mass of manganese tetroxide), 83.9g of manganese dioxide (D50=15μm) (purity 92%), 52.17g of lithium source (lithium carbonate), and low-valence metal M (… 17.7g of N (Nb2O5), 9.18g of high-valence metal N, and 2.86g of fluoride (LiF) were mixed and ground (dry ball milling, 800rpm for 1.5h, ball-to-material ratio of 1.3:1) to obtain mixed powder; II. The mixed powder is calcined (including the first stage of calcination and the second stage of calcination. The temperature of the first stage of calcination is 550℃, the heating rate is 5℃ / min, and the calcination time is 6h; the temperature of the second stage of calcination is 780℃, the heating rate is 5℃ / min, and the calcination time is 12h). After calcination, it is crushed and sieved to obtain lithium manganese oxide.

[0045] The lithium manganese oxide in this embodiment is .

[0046] Example 2 The method for preparing manganese tetroxide with a core-shell structure according to the embodiment includes the following steps: (1) Add PEG (3.2 g / L), ZIF-8 (1.07 g / L, particle size 50-100 nm) and Zn to a container (50 L reactor) containing manganese sulfate solution (1.2 mol / L). 2+ (The molar ratio with manganese sulfate is 0.5%), ammonia solution (2.0 mol / L; the flow rate of ammonia solution is 0.4 mL / min for the first 2 hours; the flow rate of ammonia solution is 1.3 mL / min for the next 4 hours, and oxygen is introduced when the flow rate of ammonia solution is 1.3 mL / min, with an oxygen flow rate of 5 L / min), and heated to 72 °C for 6 hours; (2) After the reaction is complete, the solid and liquid are separated, and the obtained solid is washed and dried to obtain the intermediate product; (3) The intermediate product is calcined (at 500°C for 1 hour under a 5% H2 / N2 atmosphere) to obtain manganese tetroxide with a core-shell structure as described in this embodiment. The manganese tetroxide with a core-shell structure prepared above is applied to the preparation of lithium manganese oxide. The preparation method of lithium manganese oxide in this embodiment includes the following steps: I. 134.2 g of manganese tetroxide (D50 = 6-7 μm) with a core-shell structure, 83.9 g of manganese dioxide (D50 = 15 μm), 52.17 g of lithium source (lithium carbonate), and low-valence metal M (as described above) 17.7g of N (Nb2O5), 9.18g of high-valence metal N, and 2.86g of fluoride (LiF) were mixed and ground (dry ball milling, 800rpm for 1.5h, ball-to-material ratio of 1.3:1) to obtain mixed powder; II. The mixed powder is calcined (including the first stage of calcination and the second stage of calcination. The temperature of the first stage of calcination is 550℃ and the time of the first stage of calcination is 6h; the temperature of the second stage of calcination is 780℃ and the time of the second stage of calcination is 12h; the heating rate is 5℃ / min). After calcination, it is crushed and sieved to obtain lithium manganese oxide.

[0047] The lithium manganese oxide in this embodiment is .

[0048] Example 3 The method for preparing manganese tetroxide with a core-shell structure according to the embodiment includes the following steps: (1) Add PEG (3.2 g / L), ZIF-8 (1.07 g / L, particle size 50-100 nm) and Zn to a container (50 L reactor) containing manganese sulfate solution (1.2 mol / L). 2+ (The molar ratio with manganese sulfate is 1.0%), ammonia solution is introduced into the container (the flow rate of ammonia solution is 0.4 mL / min for the first 2 hours; the flow rate of ammonia solution is 1.3 mL / min for the next 4 hours, and oxygen is introduced when the flow rate of ammonia solution is 1.3 mL / min, with an oxygen flow rate of 5 L / min), and the mixture is heated to 72℃ and reacted for 6 hours; (2) After the reaction is complete, the solid and liquid are separated, and the obtained solid is washed and dried to obtain the intermediate product; (3) The intermediate product is calcined (at 500°C for 1 hour under a 5% H2 / N2 atmosphere) to obtain manganese tetroxide with a core-shell structure in this embodiment.

[0049] The core-shell structured manganese tetroxide obtained above is applied to the preparation of lithium manganese oxide. The preparation method of lithium manganese oxide in this embodiment includes the following steps: I. 134.2 g of manganese tetroxide (D50 = 6-7 μm) with a core-shell structure, 83.9 g of manganese dioxide (D50 = 15 μm), 52.17 g of lithium source (lithium carbonate), and low-valence metal M (as described above) 17.7g of N (Nb2O5), 9.18g of high-valence metal N, and 2.86g of fluoride (LiF) were mixed and ground (dry ball milling, 800rpm for 1.5h, ball-to-material ratio of 1.3:1) to obtain mixed powder; II. The mixed powder is calcined (including the first stage of calcination and the second stage of calcination. The temperature of the first stage of calcination is 550℃ and the time of the first stage of calcination is 6h; the temperature of the second stage of calcination is 780℃ and the time of the second stage of calcination is 12h; the heating rate is 5℃ / min). After calcination, it is crushed and sieved to obtain lithium manganese oxide.

[0050] The lithium manganese oxide in this embodiment is .

[0051] Example 4 The only difference from Example 1 is that the mass ratio of manganese tetroxide to manganese dioxide in step I is 1:1; all other aspects are the same as in Example 1.

[0052] Example 5 The difference from Example 1 is that the mass ratio of manganese tetroxide to manganese dioxide in step I is 3:1; all other aspects are the same as in Example 1.

[0053] Example 6 The difference from Example 1 is that the calcination atmosphere in step (3) is 3% H2 / N2; the rest are the same as in Example 1.

[0054] Comparative Example 1 The difference from Example 1 is that PEG, ZIF-8, and Zn were not added in step (1). 2+ In step (3), the calcination atmosphere is pure N2 (without oxygen vacancies); the rest are consistent with Example 1.

[0055] The preparation method of lithium manganese oxide in this comparative example is the same as that in Example 1.

[0056] Comparative Example 2 The difference from Example 1 is that PEG and ZIF-8 (without core-shell structure) were not added in step (1); the rest are consistent with Example 1.

[0057] The preparation method of lithium manganese oxide in this comparative example is the same as that in Example 1.

[0058] Comparative Example 3 The difference from Example 1 is that Zn was not added in step (1). 2+The rest are consistent with Example 1.

[0059] The preparation method of lithium manganese oxide in this comparative example is the same as that in Example 1.

[0060] Comparative Example 4 The difference from Example 1 is that the calcination atmosphere in step (3) is pure N2 (without oxygen vacancies); the rest are the same as in Example 1.

[0061] The preparation method of lithium manganese oxide in this comparative example is the same as that in Example 1.

[0062] Comparative Example 5 The difference from Example 1 is that no fluoride was added in step I; all other aspects are the same as in Example 1.

[0063] Experimental Example The performance of the lithium manganese oxide prepared in the above examples and comparative examples was tested: Test method: Electrochemical performance: CR2032 button cells were assembled with lithium manganese oxide as the positive electrode (90% by mass), graphite as the negative electrode, and 1 mol / L LiPF6 / EC+DMC (1:1) as the electrolyte, and tested in the voltage range of 3.0-4.3V.

[0064] 1C capacity retention: The ratio of capacity to initial capacity after 200 cycles at 1C (148mA / g) rate.

[0065] 10C specific capacity: Discharge specific capacity at a 10C rate.

[0066] Compacted density: Lithium manganese oxide was compressed into 10mm diameter discs using a powder compactor under a pressure of 20MPa, and the mass / volume ratio was calculated.

[0067] Li + Diffusion coefficient: Calculated by intermittent titration with constant current (GITT).

[0068] Mn 3+ Content: Calculated by peak fitting of Mn 2p spectrum using XPS analysis.

[0069] Oxygen vacancy concentration: The relative content of lattice oxygen vacancies calculated from the Mn 2p spectrum.

[0070] The test results are shown in Table 1 below: Table 1

[0071] As shown in Table 1 above: Manganese tetroxide with a core-shell structure (core-shell structure + Zn) in Example 1 2+The application of pre-doped manganese oxide (with oxygen vacancies) to the preparation of lithium manganese oxide resulted in the best performance of the prepared lithium manganese oxide (for example, the 1C capacity retention of lithium manganese oxide in Example 1 reached 96.3%, which was significantly higher than that of Comparative Examples 2-4). This demonstrates that the present invention can significantly improve the performance of prepared lithium manganese oxide by preparing manganese tetroxide through the synergistic gain of multi-level regulation of "morphology-lattice-defect".

[0072] Although the surface oxygen defect eigenvalues ​​of Examples 1-5 are similar (approximately 1.2 at%), the combination with Zn 2+ Analysis of the occupancy rate (85%-92%) revealed that the stabilizing effect of the Zn-O bond is to reduce the Mn content. 3+ The key is the content (maintained at around 25%, far lower than the 30.5% of Comparative Example 1). This demonstrates that the core-shell structure of the present invention effectively locks in oxygen vacancies and suppresses the Jahn-Teller effect through Zn doping.

[0073] Combining Example 1 and Comparative Example 2, it can be seen that the core-shell structure (PEG+ZIF-8) is the key to improving compaction density (the compaction density of Comparative Example 2 is 7.7% lower than that of Example 1). Combining Example 1 and Comparative Example 3, it can be seen that: Zn 2+ Predoping effectively suppresses Mn 3+ Content (Mn in lithium manganate in Example 1) 3+ The content was reduced by 3.7% compared to Comparative Example 3. "It is worth noting that, although in comparative example 4 Mn 3+ The content is similar to that of Example 1, but its Li + The diffusion coefficient was significantly reduced. This indicates that the oxygen vacancies introduced by surface engineering (Example 1) are more conducive to constructing rapid lithium-ion transport channels than simply changing the valence state of bulk Mn, compared to the bulk material (Comparative Example 4). In Comparative Example 1, PEG, ZIF-8, and Zn were omitted when preparing manganese tetroxide. 2+ Furthermore, the step that could introduce oxygen vacancies was omitted. When the manganese tetroxide prepared in Comparative Example 1 was applied to the preparation of lithium manganese oxide, the resulting lithium manganese oxide had the worst performance. Parameter optimization range: Experimental data show that the best synergistic effect can be obtained when the oxygen vacancy concentration is 1.0-1.5 at%, which provides clear parameter guidance for industrial production.

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing manganese tetroxide with a core-shell structure, characterized in that, Includes the following steps: (1) Add PEG, ZIF-8 and Zn to the container containing manganese sulfate solution. 2+ An aqueous ammonia solution is introduced into the container, and the mixture is heated to react. (2) After the reaction is complete, the solid and liquid are separated, and the obtained solid is washed and dried to obtain the intermediate product; (3) The intermediate product is calcined to obtain manganese tetroxide with a core-shell structure.

2. The method for preparing manganese tetroxide with a core-shell structure as described in claim 1, characterized in that, In step (1), the mass ratio of PEG to ZIF-8 is 3:1; The molar ratio of ammonia in ammonia water to manganese in manganese sulfate solution is 2.0-2.5; The mass ratio of PEG to manganese sulfate in the manganese sulfate solution is 1:(56-62), Zn 2+ The molar ratio of manganese in the manganese sulfate solution is 0.5%-1.0%; The reaction temperature is 70-80℃, and the reaction time is 2-6 hours.

3. The method for preparing manganese tetroxide with a core-shell structure as described in claim 1, characterized in that, In step (1), ammonia water is first introduced at a rate of 0.3-0.5 mL / min; then ammonia water is introduced at a rate of 1.2-1.4 mL / min, and oxygen is introduced at a rate of 1-3 L / min.

4. The method for preparing manganese tetroxide with a core-shell structure as described in claim 1, characterized in that, In step (3), the calcination temperature is 400-600℃ and the calcination time is 1h; Calcination is carried out in a mixed atmosphere of H2 and N2, with H2 accounting for 3%-5% by volume.

5. A manganese tetroxide having a core-shell structure, characterized in that, The core-shell structured manganese tetroxide is prepared by the method described in any one of claims 1-4.

6. A method for preparing lithium manganese oxide, characterized in that, Includes the following steps: I. Mix and grind the core-shell structured manganese tetroxide, manganese dioxide, lithium source, low-valence metal M, high-valence metal N, and fluoride as described in claim 5 to obtain a mixed powder; wherein the low-valence metal M has a valence of divalent or trivalent, and the high-valence metal N has a valence of pentavalent or hexavalent. II. The mixed powder is calcined, and after calcination, it is crushed and sieved to obtain the lithium manganese oxide.

7. The method for preparing lithium manganese oxide as described in claim 6, characterized in that, In step I, the mass ratio of manganese tetroxide and manganese dioxide with a core-shell structure is 1:1 to 3:1; The molar ratio of lithium in the lithium source to manganese in the mixed powder is (1.05-1.2):(1.85-1.98); The molar ratio of the low-valence metal M to the high-valence metal N is (0.01-0.1):(0.01-0.05); The molar ratio of the low-valence metal M to lithium in the lithium source is (0.01-0.1):(1.05-1.15).

8. The method for preparing lithium manganese oxide as described in claim 6, characterized in that, In step II, the calcination includes a first stage of calcination and a second stage of calcination; The temperature of the first calcination stage is 450-650℃, and the calcination time is 4-8 hours; The second stage of calcination is carried out at a temperature of 700-850℃ for 8-16 hours.

9. The method for preparing lithium manganese oxide as described in claim 6, characterized in that, The low-valence metal M is selected from Mg. 2+ Al 3 + Cu 2+ and Cr 2+ At least one of them; The high-valence metal N is selected from Nb. 5+ V 5+ Cr 6+ Mo 6+ and W 6+ At least one of them; The fluoride is at least one of lithium fluoride, magnesium fluoride, and aluminum fluoride.

10. A lithium manganese oxide, characterized in that, The lithium manganese oxide is prepared by the method according to any one of claims 6-9; The chemical formula of the lithium manganese oxide is Li a Mn 2-x-y M x N y O 4-z F z Where, 1.05≤a≤1.2, 0.02≤x≤0.10, 0.01≤y≤0.05, 0.05≤z≤0.115.

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