Lithium ion battery positive electrode material and preparation method thereof

Abstract

The invention provides a lithium ion battery positive electrode material and a preparation method thereof, and relates to the technical field of batteries. According to the lithium ion battery positive electrode material and the preparation method thereof, the positive electrode material comprises the following components: a lithium iron phosphate (LiFePO4) matrix which has a three-dimensional porous structure copied by a biological template method, the aperture of which is 100 nm to 1 [mu] m, and the porosity of which is 60% to 80%; the surface of the substrate is coated with the conductive polymer layer, the conductive polymer is polypyrrole (PPy), the coating thickness is 5-20 nm, and a continuous electron transport network is formed. By optimizing the material structure, the performance is remarkably improved, the cycle stability is enhanced, the intrinsic characteristics are improved, the preparation process is more energy-saving and environment-friendly, the energy consumption is reduced, the electrochemical performance is improved, the cycle life is prolonged, the high-rate capacity is enhanced, the environment-friendly index is excellent, and the emission of harmful substances is effectively reduced; the industrial problems of traditional material structure coarsening, interface failure and process pollution are systematically solved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a lithium ion battery positive electrode material and a preparation method thereof. Background Art

[0002] Lithium-ion battery is a secondary battery (rechargeable battery) that mainly relies on the movement of lithium ions between the positive and negative electrodes to work. During the charge and discharge process, Li⁺ is embedded and de-embedded between the two electrodes. When charging, Li⁺ is de-embedded from the positive electrode and embedded into the negative electrode through the electrolyte. The negative electrode is in a lithium-rich state. The opposite is true during discharge. It is generally composed of positive electrode materials, negative electrode materials, electrolytes, diaphragms and battery casings. It has the advantages of high energy density, high operating voltage, low self-discharge, no memory effect, long cycle life, fast charging, and environmental friendliness. It is widely used in portable electronic devices, electric vehicles, energy storage systems and other fields.

[0003] The fundamental defects of the existing technology are mainly reflected in the systematic contradiction between the material structure design and the preparation process. Carbon coating technology is difficult to balance the electron conduction and ion diffusion, and the complete coverage of the carbon layer will hinder the migration of lithium ions. The hard template method relies on HF etching to remove the template, but it will introduce silicon impurities and increase the risk of lithium dendrite growth. Due to the high diffusion barrier of lithium ions, the solid phase method requires high temperature and long-term calcination, resulting in grain coarsening. The liquid phase method forms a surface passivation layer due to the adsorption of hydroxyl groups, resulting in a large loss in the first charge and discharge efficiency. In addition, the traditional process lacks precise control of key parameters (such as lithium stoichiometric ratio and coating interface bonding strength), resulting in poor batch stability of materials. At the same time, the high-energy consumption template removal process and the use of toxic reagents further increase environmental protection and cost pressures. These defects jointly limit the performance improvement and large-scale application of existing technologies. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention provides a lithium ion battery positive electrode material and a preparation method thereof, which solves the problems of low performance and environmental protection in the prior art.

[0005] To achieve the above objectives, the present invention is implemented by the following technical scheme: a positive electrode material for a lithium ion battery and a preparation method thereof, wherein the positive electrode material comprises the following components: Lithium iron phosphate (LiFePO 4 ) a matrix having a three-dimensional porous structure replicated by a bio-template method, with a pore size of 100 nm to 1 μm and a porosity of 60% to 80%; The conductive polymer layer coated on the surface of the substrate is polypyrrole (PPy), and the coating thickness is 5nm to 20nm, forming a continuous electron transport network.

[0006] A method for preparing a positive electrode material for a lithium ion battery comprises the following steps: S1. Biological template pretreatment Immerse the natural plant template in 5% NaOH solution and treat it at 80 °C for 2 hours to remove lignin and hemicellulose. After washing and drying, retain the cellulose skeleton; S2. Precursor impregnation Immerse the pretreated template in a solution containing Fe(NO 3 ) 3 ·9H 2 O, NH 4 H 2 PO 4 and LiOH. After vacuum infiltration, react at 80 °C for 6 hours to generate LiFePO 4 nanoparticles; S3. Template removal Calcine at 500 °C for 2 hours to remove the biological template and obtain a three-dimensional porous LiFePO 4 substrate; S4. In-situ polymerization Immerse the substrate in a solution containing pyrrole monomer and FeCl 3 oxidant, and stir at room temperature for 4 hours to form a PPy coating layer.

[0007] Preferably, in step S1, the biological template is selected from eucalyptus leaves, pine wood or bamboo, and the porosity of the cellulose skeleton of the natural plant template is 70%-90%.

[0008] Preferably, in step S2, the molar ratio of Fe:P:Li in the precursor solution is 1:1:1.05-1.1.

[0009] Preferably, in step S3, the calcination heating rate is 2-5 °C / min.

[0010] Preferably, in step S4, the molar ratio of pyrrole monomer to FeCl 3 is 1:0.5-1.2, and after step S4, it also includes vacuum drying at 60 °C for 12 hours.

[0011] Preferably, in step S4, the conductivity of the PPy coating layer is ≥10 S / cm.

[0012] The present invention provides a cathode material for a lithium-ion battery and a preparation method thereof. It has the following beneficial effects: The present invention provides a cathode material for a lithium-ion battery and a preparation method thereof. The core advantage of the technology of the present invention lies in achieving double breakthroughs in material structure design and preparation process through the synergistic effect of the biological template method and in-situ polymerization of conductive polymers. The present invention utilizes the three-dimensional hierarchical pores of the natural cellulose skeleton to guide LiFePO 4The nanoparticles are directionally crystallized along the pores of the template to form active substances with uniform size and uniform dispersion, solving the problem of coarse grains in the traditional solid-phase method. Through FeCl 3 The oxidant initiates in-situ polymerization of pyrrole monomers on the surface of LiFePO 4 to form coordination bonds between the PPy molecular chains and Fe³ 5 ⁺. The interfacial bonding strength is improved more than that of physical coating, and there is no risk of coating layer shedding during the cycling process. The excessive lithium in the precursor solution precisely compensates for the lithium volatilization during high-temperature calcination, so that the lithium vacancy concentration in the final product can be controlled at ≤0.5%, significantly improving the structural stability. Using a biological template to replace synthetic templates such as polystyrene, avoiding toxic gases generated by high-temperature pyrolysis, reducing the process energy consumption, realizing green preparation, solving the key bottlenecks in traditional technologies, and improving the performance and operability of the materials. Detailed implementation manners

[0013] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. Embodiment

[0014] The embodiment of the present invention provides a cathode material for a lithium-ion battery and a preparation method thereof, which specifically includes the following steps: Pretreatment of biological template Take birch fiber, treat it with 5% NaOH solution by ultrasonic treatment at 80°C for 2 h to remove lignin, and then soak it in 0.5 mol / L HCl at 60°C for 1 h to dissolve hemicellulose to obtain a purified cellulose skeleton (specific surface area >200 m² / g, pore size distribution 50 - 300 nm). Immerse the cellulose skeleton in 0.1 mol / L FeCl 3 solution for 12 h to uniformly adsorb Fe³⁺ on the pore surface (loading amount ≥3.2 wt%).

[0015] Preparation of precursor solution Dissolve LiOH·H 2 O, FeSO 4 ·7H 2 O and H 3 PO 4 in deionized water according to the molar ratio of Li:Fe:P = 1.08:1:1, add 5 wt% ascorbic acid as a reducing agent, and adjust the pH to 4.5 to form a transparent solution.

[0016] In-situ crystallization and polymerization Immerse the pretreated cellulose in the precursor solution and conduct a hydrothermal reaction at 60 °C for 12 h. Fe³⁺ initiates the formation of LiFePO 4 Heterogeneous nucleation occurs along the cellulose pores, and pyrrole vapor is simultaneously introduced (flow rate: 20 mL / min) for gas-phase polymerization. After the reaction, LiFePO 4 @PPy / cellulose composite (the thickness of the PPy coating layer is 8 - 12 nm, and the binding energy of the Fe-N coordination bond shown by XPS is 398.5 eV) is obtained.

[0017] Calcination and post-treatment In an N 2 atmosphere, heat up to 600 °C at a rate of 2 °C / min and hold for 4 h. The cellulose template is carbonized to form a porous conductive network, and simultaneously, the crystal form of LiFePO 4 is regulated (the full width at half maximum of the characteristic peak of the olivine structure shown by XRD is <0.15°). After cooling, ball mill and pass through a 400-mesh sieve to obtain the final product (particle size D50 = 85 nm, tap density ≥ 1.8 g / cm³). Examples

[0018] The examples of the present invention provide a cathode material for lithium-ion batteries and its preparation method, including a low-temperature optimization process of a cotton fiber template: Template activation Treat cotton fibers by plasma (power: 200 W, Ar gas flow rate: 50 sccm, treatment time: 10 min) to increase the density of surface active sites.

[0019] Liquid-phase coprecipitation polymerization Inject an acetonitrile solution containing 0.2 mol / L pyrrole monomer into the Fe³⁺-loaded template, add 0.05 mol / L ammonium persulfate to initiate polymerization, and react at 60 °C for 6 h to form a continuous PPy conductive layer (conductivity > 50 S / cm).

[0020] Lithium compensation regulation Determine the lithium volatilization amount to be 4.2% through TG-DSC analysis. Design the precursor with Li:Fe = 1.09 for precise compensation, and the final product has Li / Fe = 0.99 measured by ICP.

[0021] Through the synergistic effect of in-situ polymerization of biological templates and conductive polymers, the technology of the present invention achieves a breakthrough improvement in material properties and preparation processes in multiple dimensions. The three-dimensional porous structure of natural cellulose is utilized to guide the uniform growth of active substances, effectively inhibiting grain agglomeration and optimizing the microtopography, significantly shortening the lithium-ion transmission path. A conductive coating layer with strong interfacial bonding is formed by triggering polymerization with metal ions, greatly enhancing the interfacial stability of the material and ensuring the integrity of the coating structure during the cycling process. The precursor components are precisely regulated to compensate for the losses during high-temperature synthesis, significantly reducing the lattice defect concentration and enhancing the intrinsic structural stability of the material. The innovative use of renewable biological templates to replace traditional synthesis templates, combined with a medium-temperature calcination process, not only avoids the generation of harmful by-products but also significantly reduces the preparation energy consumption, realizing clean production. This technology systematically solves the long-standing technical bottlenecks such as the difficulty in regulating the microstructure of lithium battery cathode materials, the easy peeling of the conductive layer, and the large pollution during high-temperature synthesis, and demonstrates significant advantages in terms of electrochemical performance, cycle life, and production environmental protection.

[0022] Comparison Dimension Prior Art Technology of the Present Invention Detection Method Improvement Direction Structural Characteristics Grain Size Micron-sized Aggregates (>500 nm) Nanoscale monodisperse (<100 nm) SEM / TEM Size Reduced by More than 80% Specific Surface Area <10 m² / g >35 m² / g BET Nitrogen Adsorption Increased by More than 3 Times Interface Characteristics Interface Bonding Strength Physical coating (<5 MPa) Chemical Bonding (>12 MPa) Nanoindentation Test Strength Increased by 3 Times Fe Element Mobility (500 Cycles) >5% <0.3% EDS Area Scanning Mobility Reduced by 95% Structural Stability Lithium Vacancy Concentration >3% <0.5% ICP-OES Defect Concentration Reduced by 85% Lattice Distortion Rate >5% <0.8% XRD Refinement Distortion Rate Reduced by 84% Process Parameters Calcination Temperature >800℃ ≤600℃ Tube Furnace Temperature Control Temperature Reduced by 25% Energy Consumption Level >34 kWh / kg <18 kWh / kg Energy Metering System Energy Consumption Reduced by 47% Electrochemical Performance 1C Cycle Capacity Retention Rate <85% (500 weeks) >95% (500 Cycles) Blue Electric Test System Cycle Life Increased by 12% 5C Discharge Capacity <110 mAh / g >145 mAh / g Constant Current Charge and Discharge Test Rate Performance Increased by 32% Environmental Friendliness Benzene Series Emissions Toluene / Styrene Detected Not detected (LOD < 0.1 ppm) GC-MS Achieved Zero Toxic Gas Emissions HF Gas Generation Amount >50 mg / g <1 mg / g Ion Chromatography Pollutant Generation Reduced by 98% Compared with the prior art, the technology of the present invention has the grain size reduced from micron-level agglomeration to nano-level monodispersion in terms of structural characteristics, the specific surface area increased by more than 3 times, the interfacial bonding strength increased to 3 times that of the prior art through chemical bonding, the element migration rate during cycling reduced by 95%, the intrinsic stability of the material significantly enhanced, the lithium vacancies and lattice distortion rates reduced by 85% and 84% respectively, the calcination temperature of the preparation process reduced by 200 °C and the energy consumption cut by nearly half, the electrochemical performance achieved a 12% increase in cycle life and a 32% increase in high-rate capacity, and the environmental protection indicators reached zero emission of benzene series substances and a 98% reduction in HF gas emissions, systematically solving the industry problems such as the coarsening of the microstructure of traditional lithium battery cathode materials, interfacial failure, and process pollution.

[0023] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lithium ion battery positive electrode material and a preparation method thereof, characterized in that: The positive electrode material comprises the following components: A lithium iron phosphate (LiFePO4) matrix with a three-dimensional porous structure replicated by a biotemplate method, with pore sizes ranging from 100nm to 1μm and a porosity of 60% to 80%; The conductive polymer layer coated on the surface of the substrate is polypyrrole (PPy), and the coating thickness is 5nm to 20nm, forming a continuous electron transport network.

2. The method for preparing a positive electrode material for a lithium ion battery according to claim 1, characterized in that: The specific steps include: S1. Biological template pretreatment The natural plant template was immersed in 5% NaOH solution and treated at 80°C for 2 hours to remove lignin and hemicellulose, and the cellulose skeleton was retained after washing and drying; S2. Precursor Impregnation The pretreated template was immersed in a solution containing Fe(NO3)3·9H2O, NH4H2PO4 and LiOH, and reacted at 80 °C for 6 h after vacuum infiltration to generate LiFePO4 nanoparticles; S3. Template removal Calcination at 500 °C for 2 h to remove the bio-template and obtain a three-dimensional porous LiFePO4 matrix; S4. In situ polymerization The substrate was immersed in a solution containing pyrrole monomer and FeCl3 oxidant and stirred at room temperature for 4 h to generate a PPy coating layer.

3. The method for preparing a positive electrode material for a lithium ion battery according to claim 2, characterized in that: In step S1, the biological template is selected from eucalyptus leaves, pine wood or bamboo, and the cellulose skeleton porosity of the natural plant template is 70%-90%.

4. The method for preparing a positive electrode material for a lithium ion battery according to claim 2, characterized in that: The Fe:P:Li molar ratio of the precursor solution in step S2 is 1:1:1.05-1.

1.

5. The method for preparing a positive electrode material for a lithium ion battery according to claim 2, characterized in that: The calcination heating rate in step S3 is 2-5°C / min.

6. The method for preparing a positive electrode material for a lithium ion battery according to claim 2, characterized in that: The molar ratio of the pyrrole monomer to FeCl3 in step S4 is 1:0.5-1.2, and step S4 further includes vacuum drying at 60°C for 12 hours.

7. The method for preparing a positive electrode material for a lithium ion battery according to claim 2, characterized in that: In step S4, the electrical conductivity of the PPy coating layer is ≥10 S / cm.