CN-122010075-A - Sintering and shaping treatment method for improving mechanical strength of lithium iron phosphate particles

CN122010075ACN 122010075 ACN122010075 ACN 122010075ACN-122010075-A

Abstract

The application belongs to the technical field of battery materials, and particularly relates to a sintering and shaping treatment method for improving the mechanical strength of lithium iron phosphate particles. The application aims to solve the problems of easy breakage and poor cycling stability caused by coarsening of crystal grains, high porosity and large brittleness of a carbon layer of lithium iron phosphate particles in the prior art. The method comprises the steps of preparing a high specific surface area nano precursor, introducing polyvinyl alcohol and carbon nano tube to blend and coat so as to construct a carbon network and a conductive framework for enhancing toughness, performing three-stage gradient sintering, cooperatively controlling atmosphere and micro-positive pressure, adopting polyacrylonitrile or polyvinylpyrrolidone as a high molecular carbon source strengthening interface for combination, forming a 2-5 nm alumina passivation layer through atomic layer deposition, and finally performing low-energy airflow shaping. Through the regulation and control of the full chain structure, the mechanical strength, the structural stability and the electrochemical performance of the particles are obviously improved.

Inventors

LI JIANG
LI CHANGJIANG
WANG YUANBIN
WANG XU
XIE WANGJUN

Assignees

云南盈和新能源材料有限公司

Dates

Publication Date: 20260512
Application Date: 20251231

Claims (10)

1. The sintering and shaping treatment method for improving the mechanical strength of lithium iron phosphate particles is characterized by comprising the following steps of: S1, preparing a lithium iron phosphate precursor which has concentrated particle size distribution, a specific surface area of more than 30m <2 >/g, an average primary grain size of 50-150 nanometers and ferrous elements in a divalent state; s2, blending the precursor, polyvinyl alcohol and carbon nano tubes, wherein the mass adding proportion of the polyvinyl alcohol is 0.2-0.5%, and the mass adding proportion of the carbon nano tubes is 0.1-0.3%, and forming spherical secondary particles through spray drying or mechanical fusion; S3, carrying out three-stage gradient sintering on the precursor in a mixed atmosphere of inert gas and reducing gas, wherein the first stage is subjected to heat preservation at 350-450 ℃ for 60-90 minutes, the second stage is subjected to heat preservation at 550-650 ℃ for 40-60 minutes, the third stage is subjected to heat preservation at 680-720 ℃ for not more than 30 minutes, the pressure in the furnace is maintained at 1.05-1.15 standard atmospheric pressure during sintering, the volume fraction of hydrogen is 2-5%, and the oxygen partial pressure is lower than 5X 10- 5 atmospheric pressure; S4, after sintering is completed, an aluminum oxide passivation layer with the thickness of 2 to 5 nanometers is deposited on the surface of the particles by adopting an atomic layer deposition process; s5, carrying out low-energy airflow shaping on the particles subjected to passivation treatment, and removing surface burrs without damaging the internal structure.
2. The method for sintering and shaping the lithium iron phosphate particles according to claim 1, wherein the lithium iron phosphate precursor in step S1 is prepared by a coprecipitation method or a sol-gel method and does not contain alkali metal impurity ions.
3. The sintering and shaping treatment method for improving the mechanical strength of lithium iron phosphate particles according to claim 1, wherein the polyvinyl alcohol is carbonized in situ during the sintering process of step S3 to form an amorphous carbon network filled in the gaps of primary particles and connecting the contact points of the particles.
4. The sintering and shaping treatment method for improving the mechanical strength of lithium iron phosphate particles according to claim 1, wherein the carbon nanotubes in the step S2 are oriented along the particle surface under the action of shearing force in the spray drying process, and are arranged in a local orientation along the secondary particle boundary after sintering to form a three-dimensional flexible conductive framework.
5. The method for sintering and shaping the lithium iron phosphate particles to improve the mechanical strength according to claim 1, wherein a high molecular polymer carbon source is introduced to the surface of the precursor or the secondary particles, and the high molecular polymer carbon source is at least one selected from polyacrylonitrile and polyvinylpyrrolidone, and reacts with hydroxyl groups on the surface of the lithium iron phosphate in the pyrolysis process to enhance the interface bonding strength of the carbon layer and the surface of the lithium iron phosphate.
6. The method for sintering and shaping lithium iron phosphate particles according to claim 5, wherein the high molecular polymer carbon source is supported on the surface of the particles by impregnation or blending, and pyrolyzed during sintering to form a carbon layer with graphitization tendency.
7. The method for sintering and shaping the lithium iron phosphate particles to improve the mechanical strength according to claim 1, wherein the atomic layer deposition process in the step S4 uses trimethylaluminum and deionized water as precursors to deposit an aluminum oxide film at 150 ℃.
8. The method for sintering and shaping the lithium iron phosphate particles to improve the mechanical strength according to claim 1, wherein the airflow shaping in the step S5 is performed by using an airflow mill or a high-speed vortex device, and the feeding rate and the airflow speed are controlled so that the collision energy between the particles is lower than the breaking threshold.
9. The method for sintering and shaping the lithium iron phosphate particles to improve the mechanical strength according to claim 1, wherein the internal porosity of the treated lithium iron phosphate particles is lower than 3.5%, the standard deviation of primary grain size distribution is lower than 15 nm, and the surface is covered with a continuous and compact alumina passivation layer.
10. The method for sintering and shaping lithium iron phosphate particles according to claim 1, wherein the average single particle compressive strength of the obtained lithium iron phosphate particles is not less than 80 millinewtons, and the 500-week cycle capacity retention is not less than 98%.

Description

Sintering and shaping treatment method for improving mechanical strength of lithium iron phosphate particles Technical Field The invention belongs to the technical field of battery materials, and particularly relates to a sintering and shaping treatment method for improving the mechanical strength of lithium iron phosphate particles. Background Lithium iron phosphate is used as a very representative olivine structure compound in the current positive electrode material system of a lithium ion battery, and has been widely applied in the fields of power batteries and energy storage systems due to excellent thermal stability, cycle life and environmental friendliness. With the continuous pursuit of electric vehicles for high safety, long endurance and fast charging capability, and the stringent requirements of energy storage power stations for cycle durability and manufacturing cost, the comprehensive performance optimization of lithium iron phosphate materials has been gradually shifted from the improvement of single electrochemical indexes to multidimensional collaborative designs covering structural integrity, process suitability and long-term service reliability. In this context, the importance of the intrinsic mechanical strength of lithium iron phosphate particles is becoming increasingly prominent, which not only directly influences the process window stability during electrode processing, but also more deeply correlates the structural evolution behavior and capacity retention capability of the battery in long-term cycling. In the prior art, a high-temperature solid-phase method or liquid-phase synthesis combined with a subsequent sintering and carbon-coated composite process route is generally adopted for preparing lithium iron phosphate. The method has the core logic that the precursor is promoted to complete crystal phase conversion and form a highly ordered olivine crystal structure through high-temperature sintering, and simultaneously, an organic carbon source (such as glucose, sucrose and the like) is introduced to carry out in-situ carbonization under inert atmosphere, so as to construct a conductive network to make up the defect of low intrinsic electronic conductivity of the lithium iron phosphate. The technical path effectively solves the key bottlenecks of poor material conductivity, weak multiplying power performance and the like in the early development stage, and remarkably improves the reversible capacity and the power output capacity of the battery, so that the technical path becomes a mainstream process in the industry. Specifically, conventional sintering is typically carried out for several hours at a temperature above 700 ℃ to ensure adequate crystallization, while carbon coating relies on the physical attachment of an amorphous carbon layer formed by pyrolysis of a carbon source to the surface of the particles to effect the establishment of an electron path. However, with the continuous development of related technologies and the more stringent requirements of application scenarios on performance indexes, the above technical solutions have some inherent characteristics in principle, so that the technical solutions gradually show limitations in coping with new challenges. The method is based on the fact that the traditional process lacks systematic consideration on the cooperative optimization of electrochemical performance and mechanical performance, so that the structural robustness of the particles is sacrificed while the conductivity is improved. Firstly, in a sintering link, a high-temperature long-term process adopted for pursuing high crystallinity is favorable for establishing lattice integrity, excessive coarsening of crystal grains is easy to occur, so that the number of grain boundaries in the grains is obviously reduced, the grain boundaries serve as key interfaces for stress buffering and crack deflection, the loss of the grain boundaries leads to the increase of brittleness of the material, and macroscopic appearance is reduced in compression resistance and shearing resistance. Furthermore, if volatile components (such as water vapor, carbon dioxide and the like) released by the precursor in the heating process cannot be timely discharged through reasonable heating rate and atmosphere flow, closed pores are easily formed inside particles, and the micropores become stress concentration sources in subsequent electrode rolling or battery circulation to induce microcrack initiation and expansion. In addition, the conventional process is difficult to effectively control the morphology of particles, often generates secondary particles formed by hard agglomeration of primary crystal grains, and the internal bonding of the secondary particles mainly depends on Van der Waals force or weakens chemical bonds, so that the secondary particles are extremely easy to disintegrate along an agglomeration interface in the high-shear pulping or high-pressure roller pressing process to gene