Coating modification method of monocrystal lithium manganate
By performing low-temperature hydrogen activation and ternary dopant treatment on single-crystal lithium manganese oxide, combined with organic-inorganic hybrid coating and grain boundary strengthening, the problems of low activity and narrow preparation process window of single-crystal lithium manganese oxide were solved, and high capacity and stability were improved.
Patent Information
- Application Number
- CN202510956827.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-11
- Publication Date
- 2025-12-02
AI Technical Summary
The low activity, narrow material preparation process window, and low existing specific capacity of single-crystal lithium manganese oxide affect its use in the field of power batteries.
A nanoscale activation layer is formed by activating single-crystal Mn3O4 with low-temperature hydrogen. Combined with ternary dopants and two-stage sintering, an organic-inorganic hybrid coating structure is constructed. Lithium metaborate is deposited at the grain boundaries using supercritical CO2 fluid permeability to form a gradient doping system.
The surface activity and structural stability of single-crystal lithium manganese oxide were improved, the lithium-ion diffusion rate and electronic conductivity were increased, the grain boundary strength was enhanced, and the cycle stability and high-temperature performance of the material were improved.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of power battery technology, specifically to a method for coating and modifying monocrystalline lithium manganese oxide. Background Technology
[0002] Due to its excellent cycle performance, monocrystalline lithium manganese oxide has been widely used in the field of power batteries, especially in two-wheeled vehicle batteries, three-wheeled vehicle batteries, and power tools.
[0003] Currently, the production of this monocrystalline lithium manganese oxide uses monocrystalline manganese tetroxide as raw material and is prepared through solid-state sintering. The preparation process is simple, but due to the monocrystalline nature of manganese tetroxide, the activity is reduced, the material preparation process window is narrow, and precise control of the feed ratio is required. The amount of material in the sagger is small, and the gas flow rate needs to be ensured during sintering. In addition, due to the monocrystalline nature of manganese tetroxide, the high magnesium content, and the large excess lithium content, the existing specific capacity of this material is low. The discharge specific capacity of the existing material at 1C rate is only about 105 mAh / g, which is far lower than the theoretical capacity of lithium manganese oxide (148 mAh / g). This is mainly attributed to the reduction of effective reaction sites caused by monocrystalline nature and the lattice distortion caused by magnesium doping, which affects its use in the field of power batteries. Summary of the Invention
[0004] The purpose of this invention is to provide a coating modification method for single-crystal lithium manganese oxide to solve the problems mentioned in the background art.
[0005] To achieve the above objectives, the present invention provides the following technical solution, comprising the following steps:
[0006] Step 1, Precursor activation: Take single crystal Mn3O4 with an average particle size of 6-8 μm and place it in an atmosphere furnace. Introduce an argon-hydrogen mixture containing 5 vol% hydrogen and heat it to 580℃ at 5℃ / min. Hold it at that temperature for 8 hours. Then cool it to 300℃ in a nitrogen-oxygen mixture containing 2 vol% oxygen to form a nanoscale activation layer on the surface.
[0007] Step 2, Premixing and Activation: The activated single crystal Mn3O4 and dopant nanopowder are mixed in a three-dimensional mixer at a mass ratio of 95:5 for 45 minutes. The mixture is then left to stand and age in a dry environment with a relative humidity of ≤10% for 12 hours to allow the dopant to be initially adsorbed on the surface of the precursor. Then, a two-stage sintering process is performed to obtain a single crystal lithium manganese oxide matrix.
[0008] Step 3, Liquid Phase Infiltration and Polymerization: The sintered single crystal particles are dispersed in an ethanol solution containing 0.8 wt% 3,4-ethylenedioxythiophene and ultrasonically treated for 30 minutes to allow the EDOT monolayer to be adsorbed onto the particle surface. Then, an oxidant solution containing 0.5 mol / L ferric p-toluenesulfonate is added dropwise, and the reaction is stirred at 40°C for 12 hours to achieve in-situ polymerization, forming a conductive polymer underlayer of about 5 nm thickness.
[0009] Step 4: Coating layer construction: The PEDOT-coated material is placed in a fluidized bed reactor, and ammonium niobate oxalate atomized steam and lithium hydroxide micro powder are introduced. The reaction is carried out at 450℃ for 3 hours, and a gas-solid phase reaction occurs, constructing a 10-15nm thick lithium niobate nanoshell on the PEDOT layer, forming a unique organic-inorganic hybrid coating structure.
[0010] Preferably, the preparation method of the dopant nanopowder in step two is as follows: magnesium oxide, niobium ammonium oxalate and lithium fluoride are mixed in stoichiometric ratio, an appropriate amount of ethanol is added and high-energy ball milling is performed, zirconium ball:material = 8:1, 400 rpm, 2 hours, until the particle size D50 ≤ 300 nm.
[0011] Preferably, in the two-stage sintering process, the mixture product from step two is placed in an atmosphere sintering furnace, and heated to 480°C at a rate of 3°C / min and held for 10 hours under an oxygen flow rate of 5L / min to form a metastable phase structure with lithium-ion channels.
[0012] Then, the oxygen flow rate was adjusted to 8 L / min, and the temperature was increased to 780℃ at 2℃ / min and held for 15 hours. The oxygen concentration was switched every hour (fluctuating by 5-15%). The airflow pulsation effect was used to promote lattice recombination and obtain a single-crystal lithium manganese oxide matrix.
[0013] Preferably, after the coating layer is constructed, 0.3 wt% lithium metaborate is dissolved in supercritical CO2 fluid at a pressure of 15 MPa and a temperature of 50°C, and then introduced into the reactor of the coated material. The pressure is maintained for 2 hours for infiltration, and after slow depressurization, the material is heat-treated at 550°C for 3 hours to selectively deposit lithium metaborate at the grain boundaries and form a grain boundary strengthening layer.
[0014] In summary, this application includes the following beneficial technical effects:
[0015] By employing low-temperature pretreatment of single-crystal Mn3O4 in a hydrogen-containing atmosphere, surface activity is enhanced while maintaining crystal integrity, thus solving the problem of a narrow process window caused by the low reactivity of single-crystal manganese tetroxide. By controlling the dopant particle size and sintering curve, a gradient distribution of elements from grain boundaries to the grain interior is achieved, balancing structural stability and high ion diffusion rate. An inorganic ion conductor outer layer is constructed on a conductive polymer substrate, forming a dual-functional protective interface. Compared to the insufficient cycle stability of simple PEDOT coating or the poor electronic conductivity of simple lithium niobate coating, the hybrid structure achieves synergistic performance improvement. Utilizing the high permeability of supercritical CO2 fluid, lithium metaborate is selectively deposited at grain boundaries, strengthening the grain boundary structure and achieving precise nanoscale modification. Detailed Implementation
[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0017] This invention provides a technical solution comprising the following steps:
[0018] Activation of single-crystal manganese tetroxide precursor: Single-crystal Mn3O4 with an average particle size of 6-8 μm (Mn content ≥72.5%, loose packing density ≥1.50 g / cm³) is activated. 3 The sample is placed in an atmosphere furnace and argon-hydrogen mixture containing 5 vol% hydrogen is introduced. The temperature is raised to 580°C at 5°C / min and held for 8 hours. This process maintains the integrity of the single crystal structure while selectively reducing oxygen vacancy defect groups on the particle surface, significantly improving surface activity. Subsequently, it is cooled to 300°C in nitrogen-oxygen mixture containing 2 vol% oxygen to form a nanoscale activation layer on the surface.
[0019] Preparation of ternary dopant: Magnesium oxide (MgO), ammonium niobate oxalate (NH4NbO(C2O4)2), and lithium fluoride (LiF) were mixed in stoichiometric ratio (final doping concentration: Mg 0.8 at%, Nb 0.5 at%, F 1.2 at%), and an appropriate amount of ethanol was added for high-energy ball milling (zirconium balls:material = 8:1, 400 rpm, 2 hours) until the particle size D50 ≤ 300 nm. This nano-sizing process ensures uniform distribution of the dopant in subsequent processes.
[0020] Premixing and activation: The activated single crystal Mn3O4 and ternary dopant nanopowder were mixed in a three-dimensional mixer at a mass ratio of 95:5 for 45 minutes. 0.5wt% lithium stearate was added as a dispersant to prevent nanoparticle agglomeration. The mixture was left to stand and age in a dry environment with a relative humidity of ≤10% for 12 hours to allow the dopant to be initially adsorbed on the surface of the precursor.
[0021] Two-stage sintering:
[0022] A low-temperature solid-state reaction: The mixture is placed in an atmosphere sintering furnace, and heated to 480℃ at a rate of 3℃ / min under an oxygen flow rate of 5L / min and held for 10 hours. The following reactions occur during this stage:
[0023] 4Mn3O4 + Li2CO3 + 1 / 2O2 → 3LiMn2O4 + CO2 (partial lithiation)
[0024] A metastable phase structure with lithium-ion channels is formed, and the doping elements are mainly enriched in the grain boundary region.
[0025] Two-stage crystal phase reconstruction: Adjust the oxygen flow rate to 8 L / min, and raise the temperature to 780℃ at 2℃ / min, holding for 15 hours. Dynamic atmosphere control is used in this stage: the oxygen concentration is switched hourly (fluctuating between 5-15%), utilizing the gas flow pulsation effect to promote lattice reconstruction. The key reaction is:
[0026] 8Mn3O4 + 6Li2CO3 + 5O2 → 12LiMn1. 96 Mg0. o 1Nb0. o 3O3. 92 F0. o 8+6CO2
[0027] A single-crystal lithium manganese oxide matrix was obtained, with the following cell parameters: (0.8% smaller than conventional materials);
[0028] Key process parameters for two-stage sintering:
[0029]
[0030] Liquid-phase infiltration and polymerization: Sintered single-crystal particles were dispersed in an ethanol solution containing 0.8 wt% 3,4-ethylenedioxythiophene (EDOT) (solid-liquid ratio 1:10). The particles were sonicated for 30 minutes to allow the EDOT monolayer to adsorb onto the particle surface. Subsequently, an oxidant solution containing 0.5 mol / L ferric p-toluenesulfonate (Fe(OTs)3) (EDOT / Fe molar ratio 1:0.8) was added dropwise. The reaction was stirred at 40°C for 12 hours, resulting in in-situ polymerization.
[0031] EDOT+2Fe3+ →PEDOT + +2Fe 2+ +2H +
[0032] A conductive polymer substrate with a thickness of approximately 5 nm is formed;
[0033] Lithium niobate vapor deposition: The PEDOT-coated material is placed in a fluidized bed reactor, and ammonium niobate oxalate atomized vapor and lithium hydroxide micro powder are introduced. The reaction is carried out at 450°C for 3 hours, resulting in a gas-solid phase reaction.
[0034] NH4NbO(C2O4)2+LiOH→LiNbO3+2CO2+2CO+NH3+2H2O
[0035] A 10-15 nm thick lithium niobate nanoshell was constructed on the PEDOT layer, forming a unique organic-inorganic hybrid coating structure.
[0036] 0.3 wt% lithium metaborate (LiBO2) was dissolved in supercritical CO2 fluid (pressure 15 MPa, temperature 50 °C) and introduced into the coated material reactor. The mixture was pressurized and allowed to permeate for 2 hours. After slow depressurization, it was heat-treated at 550 °C for 3 hours, causing lithium metaborate to selectively deposit at the grain boundaries, forming a grain boundary strengthening layer. The following reaction occurred during this process:
[0037] LiBO2+ surface Mn-O→Li+[B--O-Mn] bonding
[0038] LiBO2 forms BO-Mn covalent bonds with Mn-O at the grain boundaries of lithium manganese oxide (bond energy 532kJ / mol), which increases the grain boundary binding energy by 30%, effectively suppressing grain boundary cracking during high-temperature cycling and achieving grain boundary strengthening.
[0039] During charging and discharging, lithium metaborate can absorb HF from the electrolyte to form stable BF4. - The compound, which prevents HF from corroding active materials, has the following reaction formula:
[0040] LiBO2 + 4HF → LiBF4 + 2H2O
[0041] Improve the high-temperature cycle life of materials.
[0042] Magnesium's lattice anchoring effect: Mg 2+ Occupy Mn 3+ The site, due to its high oxygen binding energy (Mg-O bond energy 394kJ / mol vs Mn-O bond energy 362kJ / mol), effectively suppresses Jahn-Teller distortion. The doping concentration is distributed in a gradient from the surface to the body center (0.6 at% at the surface → 1.0 at% at the body center), which balances surface stability and bulk capacity.
[0043] Enhanced electron conduction of niobium: Nb 5+ Replace Mn 4+ The introduction of free electrons subsequently increased the material's electronic conductivity to 10. -5 S / cm (approximately 10 for conventional materials) -8 (S / cm), while high-valence niobium ions reduce oxygen vacancy formation and inhibit manganese dissolution during the cycling process;
[0044] Fluorine's interfacial stabilizing properties: F - Occupy O 2- The site reduces Mn through strong electronegativity (3.98). 3+ / Mn 4+ The band gap promotes lithium-ion diffusion, and F doping also reduces the surface pH of the material to 8.5-9.0 (compared to 10-12 for conventional materials), significantly reducing electrolyte side reactions.
[0045] The ternary gradient doping system resolves the contradiction between structural stability and electrochemical activity of single-crystal lithium manganese oxide at the atomic level through the synergistic effect between elements.
[0046] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.
[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for coating and modifying single-crystal lithium manganese oxide, characterized in that: Includes the following steps: Step 1, Precursor activation: Take single crystal Mn3O4 with an average particle size of 6-8 μm and place it in an atmosphere furnace. Introduce an argon-hydrogen mixture containing 5 vol% hydrogen and heat it to 580℃ at 5℃ / min. Hold it at that temperature for 8 hours. Then cool it to 300℃ in a nitrogen-oxygen mixture containing 2 vol% oxygen to form a nanoscale activation layer on the surface. Step 2, Premixing and Activation: The activated single crystal Mn3O4 and dopant nanopowder are mixed in a three-dimensional mixer at a mass ratio of 95:5 for 45 minutes. The mixture is then left to stand and age in a dry environment with a relative humidity of ≤10% for 12 hours to allow the dopant to be initially adsorbed on the surface of the precursor. Then, a two-stage sintering process is performed to obtain a single crystal lithium manganese oxide matrix. Step 3, Liquid Phase Infiltration and Polymerization: The sintered single crystal particles are dispersed in an ethanol solution containing 0.8 wt% 3,4-ethylenedioxythiophene and ultrasonically treated for 30 minutes to allow the EDOT monolayer to be adsorbed onto the particle surface. Then, an oxidant solution containing 0.5 mol / L ferric p-toluenesulfonate is added dropwise, and the reaction is stirred at 40°C for 12 hours to achieve in-situ polymerization, forming a conductive polymer underlayer of about 5 nm thickness. Step 4: Coating layer construction: The PEDOT-coated material is placed in a fluidized bed reactor, and ammonium niobate oxalate atomized steam and lithium hydroxide micro powder are introduced. The reaction is carried out at 450℃ for 3 hours, and a gas-solid phase reaction occurs, constructing a 10-15nm thick lithium niobate nanoshell on the PEDOT layer, forming a unique organic-inorganic hybrid coating structure.
2. The coating modification method for single-crystal lithium manganese oxide according to claim 1, characterized in that: The preparation method of the dopant nanopowder in step two is as follows: magnesium oxide, niobium ammonium oxalate and lithium fluoride are mixed in stoichiometric ratio, and an appropriate amount of ethanol is added for high-energy ball milling. The ratio of zirconium balls to material is 8:1, 400 rpm, 2 hours, until the particle size D50 ≤ 300 nm.
3. The coating modification method for single-crystal lithium manganese oxide according to claim 1, characterized in that: In the two-stage sintering process, the mixture product from step two is placed in an atmosphere sintering furnace and heated to 480°C at a rate of 3°C / min under an oxygen flow rate of 5L / min and held for 10 hours to form a metastable phase structure with lithium-ion channels. Then, the oxygen flow rate was adjusted to 8 L / min, and the temperature was increased to 780℃ at 2℃ / min and held for 15 hours. The oxygen concentration was switched every hour (fluctuating by 5-15%). The airflow pulsation effect was used to promote lattice recombination and obtain a single-crystal lithium manganese oxide matrix.
4. The coating modification method for single-crystal lithium manganese oxide according to claim 1, characterized in that: After the coating layer was constructed, 0.3 wt% lithium metaborate was dissolved in supercritical CO2 fluid at a pressure of 15 MPa and a temperature of 50 °C. The solution was then introduced into the reactor containing the coated material. The solution was pressurized and allowed to permeate for 2 hours. After slowly depressurizing, the solution was heat-treated at 550 °C for 3 hours to allow lithium metaborate to selectively deposit at the grain boundaries, forming a grain boundary reinforcement layer.