Lithium iron phosphate positive electrode material, preparation method thereof, and lithium ion battery
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Solution Overview
Problem
Lithium iron phosphate positive electrode materials exhibit poor low-temperature and rate performance, along with high magnetic material content, which hinders their suitability for power batteries due to issues like self-discharge and safety concerns, despite advancements in synthesis methods like solid-phase and hydrothermal synthesis.
Innovation Solution
A lithium iron phosphate positive electrode material with a formula of LiFe1-xMxPO4/C, where 0<x≤0.05, and M is selected from elements like Mg, Al, Zr, Ti, Co, V, Mn, W, Sn, Nb, and Mo, is synthesized using a method involving hydrothermal reaction, sand milling, and sintering, with the addition of a dispersant and grain growth inhibitor to control particle size and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If solid-phase method is used to prepare lithium iron phosphate, then manufacturing cost is low and capacity is high, but particle size is large resulting in poor low-temperature and rate performances
Solution Approach 1:
The patent divides the particle size control into multiple stages: hydrothermal synthesis produces primary particles of 5-50nm, followed by controlled aggregation to form secondary particles of 1-5μm. This segmentation approach allows the material to maintain small primary particle characteristics for good rate performance while forming larger secondary particles for practical handling and capacity
Solution Approach 2:
The patent changes the synthesis method from solid-phase to hydrothermal method, fundamentally altering the reaction conditions (aqueous environment, temperature, pressure) to produce smaller primary particles with better conductivity while maintaining manufacturing feasibility
2Speed
If wet synthesis is used to prepare lithium iron phosphate, then particle size is small improving low-temperature and rate performances, but many impurity phases exist resulting in high magnetic material content and poor high-temperature and cycle performances
Solution Approach 1:
The patent extracts and removes impurity phases through multiple washing steps using deionized water and dilute acid solutions during the hydrothermal process. This extraction of harmful impurities reduces magnetic material content while preserving the beneficial small particle size characteristics
Solution Approach 2:
The patent creates a composite structure with core LiFePO4 particles surrounded by a carbon coating layer. This composite approach improves electrical conductivity and stabilizes the particle structure, enhancing both rate performance and cycle stability simultaneously
3Quantity of substance
If solid-phase method is used to prepare lithium iron phosphate, then capacity is high, but magnetic material content is high causing self-discharge and safety problems
Solution Approach 1:
The patent converts the potential harm of iron impurities by using highly pure reagents and controlled hydrothermal conditions that prevent impurity formation. The careful control of reaction parameters transforms a potentially problematic synthesis into one that produces high-purity material with low magnetic content
4Reliability
If lithium iron phosphate material is used, then safety and cycle life are good, but low-temperature and rate performances are poor
Solution Approach 1:
The patent applies local quality improvement by coating only the surface of each particle with carbon and conductive materials. This localized treatment enhances electrical conductivity at the particle surface where charge transfer occurs, improving rate performance without affecting the bulk safety characteristics of the LiFePO4 structure
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The approach results in a material with improved low-temperature and rate performance, reduced magnetic content, and enhanced high-temperature storage and cycle performance, addressing the limitations of existing lithium iron phosphate materials.
Implementation Method 1
A lithium salt, a phosphoric acid and an iron salt are uniformly mixed and then performed hydrothermal reaction in the presence of a solvent under an inert atmosphere
Implementation Method 2
An organic carbon source, a dispersant and a grain growth inhibitor are added to the second slurry, and performed sand milling under an inert atmosphere
Implementation Method 3
The precursor is sintered and then performed jet milling to obtain the lithium iron phosphate positive electrode material
Implementation Method 4
The precursor is sintered and then performed jet milling to obtain the lithium iron phosphate positive electrode material
Data Source
AI summary
A lithium iron phosphate positive electrode material, a preparation method thereof, and a lithium ion battery are disclosed. The lithium iron phosphate positive electrode material has an expression formula of LiFe1-xMxPO4/C, in which, 0<x≤0.05; and M is at least one element selected from Mg, Al, Zr, Ti, Co, V, Mn, W, Sn, Nb and Mo. The lithium iron phosphate positive electrode material has a particle size distribution meeting (D90-D10)/D50=1-2.17; and the magnetic material content in the lithium iron phosphate positive electrode material is 850-900 ppm (w/w).