LFP Positive Electrode Particle Structure for Stronger Collector Adhesion
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Solution Overview
Problem
Lithium iron phosphate-based positive electrodes in lithium secondary batteries suffer from low adhesive force between the active material layer and the current collector, leading to deintercalation and increased battery resistance, which reduces capacity.
Innovation Solution
Incorporating a combination of large-sized lithium iron phosphate particles with facets and smaller-sized particles within the positive electrode active material layer, where the large particles have an average diameter of 2-8 μm and the smaller particles are less than 1 μm, to enhance the adhesive force through increased contact area and improved mixing with the binder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the average particle diameter of lithium iron phosphate is reduced to improve lithium ion mobility, then lithium ion mobility is improved, but the specific surface area increases causing severe particle aggregation, which reduces the adhesive force between the positive electrode current collector and the positive electrode active material layer
Solution Approach 1:
The patent applies local quality by creating a heterogeneous particle size distribution within the positive electrode active material layer. Small particles (<1 μm) are concentrated in specific regions to enhance lithium ion mobility and electrical conductivity, while large particles (1-8 μm) are distributed in other regions to provide structural support and strong adhesive force to the current collector. This spatial differentiation of particle functions resolves the contradiction between mobility and adhesion.
Solution Approach 2:
The patent uses a composite structure combining lithium iron phosphate particles of different sizes within the same electrode layer. The multi-scale particle composite (small particles for conductivity, large particles for mechanical strength) creates a synergistic effect where the advantages of each particle size range are utilized simultaneously, overcoming the limitations of using a single particle size distribution.
2Reliability
If small lithium iron phosphate particles are used to improve lithium ion mobility, then electrical conductivity is improved, but particle aggregation occurs severely, resulting in poor mixing with the binder and reduced adhesive force
Solution Approach 1:
The patent segments the particle population into distinct size categories (small particles <1 μm and large particles 1-8 μm) with different functional roles. This segmentation prevents uniform aggregation because the size difference creates physical separation and reduces the tendency of particles to clump together uniformly, thereby improving mixing homogeneity while maintaining the electrical conductivity benefits of small particles.
Solution Approach 2:
The patent changes the particle size parameter to create a bimodal or multimodal distribution rather than a unimodal distribution. By introducing particles with significantly different sizes, the system alters the packing and mixing behavior, preventing severe aggregation and improving the homogeneity of the active material layer composition.
3Ease of manufacture
If the positive electrode adhesive force is low, then electrode preparation and charging/discharging proceed without structural issues, but deintercalation of the positive electrode active material layer occurs, resulting in increased battery resistance and reduced capacity
Solution Approach 1:
The patent applies preliminary action by ensuring strong adhesive bonding between the positive electrode active material layer and the current collector through the use of large particles during the electrode preparation stage. This preliminary strengthening of the interface prevents subsequent deintercalation issues during charging/discharging cycles, thereby maintaining battery capacity and reliability throughout the battery's operational life.
Data Source
AI summary
A positive electrode includes a positive electrode active material layer, and the positive electrode active material layer includes a first lithium iron phosphate and a second lithium iron phosphate as a positive electrode active material, the first lithium iron phosphate has an average particle diameter D50 grater than that of the second lithium iron phosphate and at least one facet, and when the cross section of the positive electrode is observed with a scanning electron microscope (SEM), the cross section of the first lithium iron phosphate has at least one side having a length of 2 μm or more.