Bimodal Cathode Particle Distribution for Dense Li-Ion Electrodes
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Solution Overview
Problem
The low compaction density and poor kinetic performance of lithium iron phosphate positive electrode materials in lithium-ion secondary batteries due to increased particle size, leading to longer lithium-ion transmission paths and decreased gram capacity and rate performance.
Innovation Solution
A secondary battery design with a positive electrode active material having a bimodal particle size distribution, characterized by specific ratios and ranges of particle sizes and areas, optimizing the distribution to balance compaction density and kinetic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If the particle size of primary particles is increased to improve compaction density, then the compaction density is improved, but the lithium-ion transmission path becomes longer leading to deterioration of kinetic performance and decrease in gram capacity
Solution Approach 1:
The positive electrode active material is segmented into two distinct particle size ranges: small particles (0.5-2.0 μm) for high surface area and good kinetic performance, and large particles (2.0-5.0 μm) for high compaction density. This segmentation allows each particle size to fulfill different functional requirements simultaneously.
Solution Approach 2:
Different regions of the electrode are populated with different particle sizes optimized for their local function: smaller particles dominate in regions requiring fast lithium-ion transport (improving gram capacity and rate performance), while larger particles are distributed in regions where compaction density is prioritized. The controlled mixed distribution creates local quality variations throughout the electrode structure.
2Volume of stationary object
If the particle size of primary particles is increased to improve compaction density, then the compaction density is improved, but the gram capacity and rate performance significantly decrease
Solution Approach 1:
The particle population is segmented into two size classes with specific volume ratios (30-70% small particles, 30-70% large particles). This segmentation ensures that sufficient small particles are present to maintain high gram capacity through their large surface area, while enough large particles are included to achieve high compaction density.
Solution Approach 2:
The invention changes the particle size distribution parameters from a single-size distribution to a bimodal distribution with specific control over mean particle sizes (0.5-2.0 μm and 2.0-5.0 μm) and their volume ratios. This parameter change optimizes both gram capacity (benefiting from small particles) and compaction density (benefiting from large particles) simultaneously.
3Ease of manufacture
If a single particle size distribution is used, then the manufacturing process is simple, but the compaction density and kinetic performance are insufficient
Solution Approach 1:
The manufacturing process is segmented into distinct steps for producing small and large particles, followed by a controlled mixing step. This segmentation of the manufacturing process enables precise control over the final particle size distribution, ensuring optimal kinetic performance while maintaining manufacturing feasibility through standardized processing steps.
Solution Approach 2:
The positive electrode active material is created as a composite particle size distribution system, combining two different particle size populations in specific proportions. This composite approach leverages the advantages of both small and large particles, achieving superior kinetic performance and compaction density that neither single-size distribution could achieve alone.
Data Source
Figure 1
AI summary
Disclosed herein are a secondary battery and an electrochemical device. The secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; where the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material has a particle size distribution curve including a first peak and a second peak; the secondary battery satisfies: 0.22 ≤ K ≤ 2.13, and K = Dn50 × (Dv90 - Dv10) / Dv50; based on that a sum of an area proportion of the first peak and an area proportion of the second peak is 100%, the area proportion of the first peak is S1%, the area proportion of the second peak is S2%, and R = S1 / S2, 0.25 ≤ R ≤ 2.33. The present application achieves an increase in compaction density, a reduction in lithium-ion transmission path, and an increase in the energy density of the secondary battery by optimizing the particle size distribution of the positive electrode active material, restricting the volume-based distribution curve to show a bimodal pattern, and grading the large and small particle sizes.