A method for preparing lithium manganate using a coated manganate

Abstract

This invention discloses a method for preparing lithium manganese oxide using coated manganese oxides. Mn3O4 is treated at low temperature using gas plasma and then annealed to obtain Mn2O3-coated Mn3O4, referred to as Mn3O4@Mn2O3. Mn3O4@Mn2O3 is then treated at low temperature using gas plasma and annealed to coat the Mn2O3 layer with MnO2, forming a coated manganese oxide. The coated manganese oxide is then used as a manganese source and undergoes a high-temperature solid-state reaction with a lithium source to obtain lithium manganese oxide. This invention, through different outer coating layers, induces the formation of LMO with fewer structural defects such as oxygen vacancies, reducing side reactions between LMO and the electrolyte, lowering interfacial impedance, achieving better stability, and improving battery performance.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology and relates to lithium-ion battery technology, specifically a method for preparing lithium manganese oxide using coated manganese oxide. Background Technology

[0002] Spinel-type lithium manganese oxide (LiMn2O4) (LMO) cathode materials have wide applications in the field of power lithium batteries for two-wheeled and three-wheeled vehicles due to their low raw material cost and excellent low-temperature performance. However, LMO materials face several challenges due to their structure and elemental characteristics: during deep discharge, LMO is prone to the Jameer-Taylor effect, causing the crystal structure to change from cubic to tetragonal, resulting in decreased conductivity and affecting lithium-ion diffusion within the crystal lattice; the hydrofluoric acid produced when lithium salt LiPF6 comes into contact with trace amounts of water in the electrolyte causes trivalent manganese ions to undergo a disproportionation reaction, producing divalent manganese ions, which then dissolve in the electrolyte. This not only causes structural collapse of the cathode but also damages the structure of the anode after the dissolved manganese is reduced on the negative electrode side; oxygen defects caused by the synthesis conditions weaken the bonding between transition metal ions and oxygen, exacerbating manganese dissolution and accelerating battery capacity decay.

[0003] Currently, most industry practices use electrolytic manganese dioxide (EMD) or manganese tetroxide (Mn3O4) as precursors to produce lithium manganese oxide via high-temperature solid-state reaction at 700-850℃ with lithium carbonate (Li2CO3) or lithium hydroxide (LiOH). Among these, manganese tetroxide, as a manganese source, outperforms manganese dioxide in terms of phase purity, electrochemical cycle stability, and particle uniformity. However, LMO synthesized from Mn3O4 precursors exhibits numerous active sites or defects on the particle surface, making them prone to side reactions with the electrolyte, catalyzing electrolyte decomposition, forming a thick and unstable solid electrolyte interfacial film, and increasing interfacial impedance. Furthermore, the average valence state of manganese in Mn3O4 is +2.67, requiring a long time to complete lithiation and oxidation with Li2CO3, a process that can easily lead to localized compositional inhomogeneity. Therefore, adjusting the composition and structural modification of the manganese oxide precursor are crucial for the synthesis of safe and stable LMOs. Summary of the Invention

[0004] To overcome the shortcomings of LMO synthesis from Mn3O4, this invention mainly employs the following technical means: Mn3O4 is pretreated to transform its outer layer into Mn2O3 + MnO2. Then, LMO is generated by reacting it with a lithium source and oxygen using a high-temperature solid-state reaction method common in industrial production. Through different outer coating layers, the induced LMO exhibits fewer structural defects such as oxygen vacancies, reducing side reactions between LMO and the electrolyte, lowering interfacial impedance, achieving better cycle stability, and improving battery performance.

[0005] The present invention adopts the following technical solution.

[0006] A method for preparing lithium manganese oxide using coated manganese oxide includes the following steps: (1) Mn3O4 is treated with gas plasma at low temperature and then annealed to obtain Mn2O3-coated Mn3O4, which is called Mn3O4@Mn2O3; (2) Mn3O4@Mn2O3 was treated with gas plasma at low temperature and then annealed to coat MnO2 on the Mn2O3 layer, which is a coated manganese oxide; (3) Using the coated manganese oxide as a manganese source and lithium source, a high-temperature solid-phase reaction is carried out to obtain lithium manganese oxide.

[0007] In this invention, the gas includes helium and oxygen; preferably, the gas is a mixture of helium and oxygen; more preferably, the volume ratio of helium to oxygen is (85-95):(5-15), for example, 90:10.

[0008] In this invention, the low temperature is 120-180°C, preferably 130-170°C, and even more preferably 140-160°C.

[0009] In this invention, the low-temperature treatment time is 15 to 60 minutes; preferably, the low-temperature treatment time is 20 to 50 minutes; more preferably, the low-temperature treatment time is 25 to 40 minutes.

[0010] In this invention, the annealing temperature is 250–370°C and the time is 1–3 hours; preferably, the annealing temperature is 270–350°C and the time is 1.5–2.5 hours; more preferably, the annealing temperature is 280–330°C and the time is 1.8–2.3 hours.

[0011] In this invention, the lithium source includes one or more of Li2CO3, LiOH, LiNO3, and LiCH3COO.

[0012] In this invention, the solid-phase reaction is carried out under air conditions.

[0013] In this invention, the solid-phase reaction temperature is 700℃~900℃ and the time is 12h~20h; preferably, the solid-phase reaction temperature is 750℃~850℃ and the time is 15h~18h; as an example, the solid-phase reaction is calcined at 800℃ for 16h.

[0014] This invention discloses lithium manganese oxide prepared by the above-described method for preparing lithium manganese oxide using coated manganese oxide.

[0015] This invention discloses the application of lithium manganese oxide prepared by the above-described method of preparing lithium manganese oxide using coated manganese oxide in the preparation of lithium-ion batteries.

[0016] This invention discloses the application of lithium manganese oxide prepared by the above-described method of preparing lithium manganese oxide using coated manganese oxide in the preparation of lithium-ion battery cathodes.

[0017] This invention discloses a lithium-ion cathode, comprising lithium manganese oxide prepared by the above-described method for preparing lithium manganese oxide using coated manganese oxide.

[0018] This invention discloses a lithium ion, including lithium manganese oxide prepared by the above-described method for preparing lithium manganese oxide using coated manganese oxide.

[0019] This invention utilizes manganese trioxide (Mn2O3) and MnO2 to coat Mn3O4, forming a three-layer core-shell structure consisting of MnO2, Mn2O3, and Mn3O4 from the outside in. During the high-temperature solid-state reaction with the lithium source, the main processes are lithium intercalation and lithiation. The reaction path is more direct and mild, reducing structural defects that lead to capacity decay and improving the structural stability of the material. The final product is LMO, without introducing additional impurity elements or other coating layers to reduce the specific capacity of the cathode. This helps to form a regular and complete spinel structure, and the obtained LMO material usually has a high initial capacity and good rate performance. Attached Figure Description

[0020] Figure 1 This is a SEM image of commercially available Mn3O4 powder.

[0021] Figure 2 This is a SEM image of Mn3O4@Mn2O3.

[0022] Figure 3 The image shows the XRD pattern of Mn3O4@Mn2O3.

[0023] Figure 4 SEM images of Mn3O4@Mn2O3@MnO2.

[0024] Figure 5 The image shows the XRD patterns of Mn3O4@Mn2O3@MnO2.

[0025] Figure 6 This is a SEM image of Mn3O4@MnO2.

[0026] Figure 7 The image shows the XRD pattern of Mn3O4@MnO2.

[0027] Figure 8 This is a SEM image of the product LMO. Detailed Implementation

[0028] The industry typically uses electrolytic manganese dioxide (EMD) or manganese tetroxide (Mn3O4) as precursors to produce lithium manganese oxide by high-temperature solid-state reaction with lithium carbonate (Li2CO3) or lithium hydroxide (LiOH) at 700-850℃. However, the resulting product has technical weaknesses when used in lithium-ion batteries. Current reports describe a method where manganese sulfate solution, a precipitant, and a complexing agent are added concurrently to a reactor. Under an oxidizing agent, a manganese tetroxide substrate material is first prepared. Then, under a strong oxidizing atmosphere, some of the manganese oxidation state is oxidized from +2 to +3 to obtain a composite manganese oxide including manganese trioxide. This composite is then mixed with lithium carbonate and calcined to obtain lithium manganese oxide cathode material. This method, which uses liquid-phase co-precipitation + secondary oxidation to prepare composite manganese oxides and then synthesizes LMO, involves the repeated use of precipitants, complexing agents, and ripening agents (such as surfactants, sodium hypochlorite, and ammonium bicarbonate). These organic or inorganic salts are prone to remain in the final precursor as impurities. During high-temperature sintering, they can easily introduce heteroatoms into LMO, contaminating the LMO lattice and reducing its electrochemical performance. Furthermore, the formation of Mn2O3 depends on the second introduction of a strong oxidant (such as ozone, hydrogen peroxide, and sodium persulfate). This intense chemical oxidation process is difficult to control and can easily lead to over-oxidation or under-oxidation of the substrate particles. This is one of the limitations of this method for industrial application.

[0029] This invention employs a novel technical approach, transforming the outer layer of pretreated Mn3O4 into Mn2O3+MnO2. Subsequently, it utilizes a high-temperature solid-state reaction method, typical of industrial production, to react with a lithium source and oxygen to generate LMO. By encapsulating the LMO with different outer coating layers, the induced LMO exhibits fewer structural defects, such as oxygen vacancies, reducing side reactions between the LMO and the electrolyte, lowering interfacial impedance, achieving better cycle stability, and improving battery performance. In particular, the pretreatment method of this invention is simpler and more controllable than chemical reaction methods, which is beneficial for industrial production.

[0030] The following specific experiments illustrate the technological advancements of this invention. The raw materials used are existing products, and the specific preparation operations and performance testing are conventional techniques that meet the conventional requirements for lithium-ion batteries.

[0031] Example 1 1. Mn3O4@Mn2O3 (Mn2O3 coated with Mn3O4) Commercially available Mn3O4 powder was evenly spread in a quartz vessel, which was then placed in the reaction chamber of an existing low-temperature plasma treatment device. Working gas was introduced into the reactor chamber at a volume ratio of helium to oxygen of 90:10. The plasma power supply was turned on, and the Mn3O4 precursor powder was irradiated at a low temperature of 150°C for 30 minutes. Then, the plasma power supply was turned off, and air was introduced at 300°C for 2 hours to complete crystallization, resulting in Mn3O4@Mn2O3. The outer layer of the Mn3O4 particles was transformed into Mn2O3.

[0032] Figure 1 This is a SEM image of commercially available Mn3O4 powder. Figure 2 The above SEM image shows Mn3O4@Mn2O3. Based on the original structure, the surface is coated with polycrystalline Mn2O3, a fact supported by the XRD pattern of Mn3O4@Mn2O3. (See [link]). Figure 3 .

[0033] 2. Mn3O4@Mn2O3@MnO2 (MnO2 coating Mn2O3 coating Mn3O4, a three-layer structure) The product Mn3O4@Mn2O3 obtained in step (1) was placed in a quartz vessel again. The quartz vessel was placed in the reaction chamber of an existing low-temperature plasma treatment device. The working gas was introduced into the reactor chamber at a volume ratio of helium to oxygen of 90:10. The plasma power supply was turned on and irradiated at a low temperature of 150°C for 30 minutes. The plasma power supply was turned off and air was introduced at 300°C for annealing for 2 hours to complete crystallization, forming a three-layer core-shell structure of MnO2, Mn2O3, and Mn3O4 from the outside to the inside.

[0034] Figure 4 The above SEM images show Mn3O4@Mn2O3@MnO2. The Mn2O3 surface is coated with a layer of MnO2, a fact supported by the XRD patterns of Mn3O4@Mn2O3@MnO2. (See [link to relevant documentation]). Figure 5 .

[0035] Comparative Example 1: Mn3O4@MnO2 (Mn3O4 coated with MnO2) Mn3O4 powder was evenly spread in a quartz vessel and placed in the reaction chamber of an existing low-temperature plasma treatment device. The working gas was introduced into the reactor chamber at a volume ratio of helium to oxygen of 90:10. The plasma power supply was turned on, and the Mn3O4 precursor powder was irradiated at a low temperature of 150°C for 90 minutes. The plasma power supply was then turned off, and the precursor was annealed in air at 300°C for 2 hours to complete crystallization, thus obtaining Mn3O4@MnO2.

[0036] Figure 6The above SEM image shows that the Mn3O4 surface is coated with a layer of MnO2, which is supported by the XRD pattern of Mn3O4@MnO2. (See [link to relevant documentation]). Figure 7 .

[0037] Example 2 Sintering LMO was prepared by calcining the above three precursors (Mn3O4@Mn2O3, Mn3O4@Mn2O3@MnO2, Mn3O4@MnO2) and Mn3O4, Mn2O3, and MnO2 (commercially available) separately in molar ratios of 1.53:1, 1.39:1, 2.06:1, 4:3, 2:1, and 4:1 with lithium source Li2CO3 in a muffle furnace at 800°C for 16 hours under air-purifying conditions.

[0038] Figure 8 The image shows the SEM image of the LMO product mentioned above. Mn3O4@Mn2O3@MnO2 was used as the manganese source, and the product was Mn3O4@Mn2O3@MnO2-LMO.

[0039] Comparison Example Currently, commercially available lithium manganese oxide is the most widely used product in industry and is the mainstream product in production.

[0040] The application examples employ conventional methods to prepare the batteries, as briefly described below: (1) Preparation of positive electrode A positive electrode slurry was prepared by stirring and dispersing 3.5 wt% conductive carbon, 6.3 wt% CNTs, 5.2 wt% polyvinylidene fluoride, and the balance lithium manganese oxide (the sum of the mass percentages of the four components being 100%) in N-methylpyrrolidone. This slurry was then coated onto a 15 μm aluminum foil current collector. After cold pressing, slitting, and cutting, the positive electrode sheet was obtained. The coating density was 12 mg / cm² on one side of the positive electrode. 2 .

[0041] (2) The negative electrode is lithium metal.

[0042] (3) The electrolyte is a conventional organic carbonate system containing FEC (fluoroethylene carbonate) and DTD (dithiobistetrahydrothiazolinone).

[0043] (4) A 16μm thick polyethylene microporous membrane coated with an alumina coating is selected, which is a conventional product.

[0044] (5) Preparation of lithium-ion batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The stacked electrodes form a bare cell, which is then inserted into the cell casing. The lithium-ion battery is obtained through existing processes such as baking, electrolyte injection, formation, and sealing.

[0045] Except for lithium manganese oxide, all of the above preparation methods are existing products, and the specific preparation methods are all conventional technologies.

[0046] Shelving performance: After being fully charged at 55℃ for 7 days, the customer requires a capacity retention rate of >90% and a capacity recovery rate of >93% after shelving.

[0047] The performance results of the prepared LMO and the commercially available prepared LMO are shown in the table below.

[0048]

[0049] Comparative Example 2 Physically mixing Mn3O4, Mn2O3, and MnO2 yields a mixed powder of Mn3O4, Mn2O3, and MnO2. This powder is then sintered at high temperature with a lithium source, Li2CO3, to prepare LMO. However, this process does not meet the customer's requirements for shelf life performance.

[0050] This invention employs a simple low-temperature, ambient-pressure plasma treatment method to synthesize a three-layer core-shell structure of MnO2 + Mn2O3 + Mn3O4. This method possesses strong universality and controllability, laying the foundation for the subsequent sintering of high-performance LMOs. The reaction with the lithium source is easier and milder, requiring a lower energy barrier. During the high-temperature solid-state reaction, the MnO2 shell preferentially reacts with Li2CO3, releasing oxygen and creating a strongly oxidizing atmosphere. This atmosphere provides a strong oxidizing environment for the internal Mn2O3 and Mn3O4. Mn2O3 reacts with the lithium source to form a lithium manganese oxide-rich shell. This shell acts as a template and buffer layer for the reaction between the internal Mn3O4 core and lithium, guiding the core material towards a more ordered spinel structure, improving the reaction pathway, reducing the overall reaction temperature and time, and helping to oxidize and repair oxygen vacancies that may be generated in the bulk phase of the internal Mn3O4 during the reaction. This results in an LMO with an oxygen stoichiometry closer to the ideal state. Simultaneously, the strong oxidizing environment is beneficial for the oxidation of MnO2 and Mn2O3. 3+ By controlling the temperature within a stable range, reducing the Gaines-Taylor distortion, forming a stable and dense main shell, and reducing interfacial side reactions with the electrolyte, it has higher initial capacity and rate performance, excellent cycle stability and low interfacial impedance, alleviates the problem between the bulk phase and the interface, and comprehensively balances capacity and cycle life, making it suitable for use as an all-around LMO.

[0051] The precursor coating scheme provided by this invention does not introduce heteroatoms and impurity coating layers. The MnO2, Mn2O3 coating layers and Mn3O4 core can all be converted into the target product, spinel lithium manganese oxide, after high-temperature solid-state reaction with the lithium source. While not losing the specific capacity of the cathode material, the surface morphology and surface states of the final product LMO are controlled by the MnO2 and Mn2O3 shell, thereby improving the intrinsic performance of LMO.

[0052] Storage performance refers to the ability of a battery to retain its capacity, internal resistance, structure, and safety over time and temperature under static, non-charge / discharge conditions. It is a key performance indicator besides cycle life. Lithium manganese oxide (LMO) materials are prone to capacity decay and increased internal resistance during storage due to manganese leaching, which is one of the factors limiting their application. To address the needs of application users, this invention adopts a novel technical approach, using a high-temperature solid-state reaction between a MnO2 and Mn2O3 coating layer and an Mn3O4 core with a lithium source to convert it into the target product, spinel lithium manganese oxide, thereby improving the intrinsic properties of LMO and meeting application requirements.

Claims

1. A method for preparing lithium manganese oxide using coated manganese oxide, comprising the following steps: (1) Mn3O4 was subjected to low-temperature treatment with gas plasma and then annealed to obtain Mn3O4@Mn2O3; (2) Mn3O4@Mn2O3 was subjected to low-temperature treatment with gas plasma and then annealed to obtain coated manganese oxide; (3) Using the coated manganese oxide as a manganese source and lithium source, a high-temperature solid-phase reaction is carried out to obtain lithium manganese oxide.

2. The method for preparing lithium manganese oxide using coated manganese oxide according to claim 1, characterized in that, The gases include helium and oxygen.

3. The method for preparing lithium manganese oxide using coated manganese oxide according to claim 1, characterized in that, The low temperature is 120–180℃; the low temperature treatment time is 15–60 minutes.

4. The method for preparing lithium manganese oxide using coated manganese oxide according to claim 1, characterized in that, The annealing temperature is 250–370℃, and the time is 1–3 hours.

5. The method for preparing lithium manganese oxide using coated manganese oxide according to claim 1, characterized in that, The lithium source includes one or more of Li2CO3, LiOH, LiNO3, and LiCH3COO.

6. The method for preparing lithium manganese oxide using coated manganese oxide according to claim 1, characterized in that, The solid-phase reaction is carried out under air conditions; the temperature of the solid-phase reaction is 700℃~900℃, and the time is 12h~20h.

7. Lithium manganese oxide prepared by the method for preparing lithium manganese oxide using coated manganese oxide as described in any one of claims 1 to 6.

8. The application of lithium manganese oxide as described in claim 7 in the preparation of lithium-ion batteries, or in the preparation of lithium-ion battery cathodes.

9. A lithium-ion cathode comprising the lithium manganese oxide as described in claim 7.

10. A lithium ion comprising the lithium manganese oxide of claim 7.

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