LFP Cathode Particle Distribution for Density and Rate Balance
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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 area proportions, optimizing the compaction density and kinetic performance through a balanced distribution of large and small particles.
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 patent applies local quality by creating a bimodal particle size distribution where different regions of the electrode contain particles of different sizes. Small particles (0.5-2 μm) are distributed throughout to provide short lithium-ion transmission paths and high kinetic performance, while large particles (2-5 μm) are also present to increase compaction density. This spatial distribution of different particle qualities resolves the contradiction between compaction density and lithium-ion transmission speed.
Solution Approach 2:
The patent segments the particle size distribution into two distinct modes or populations. Rather than using a single particle size, the invention divides the particle population into small particles for kinetic performance and large particles for compaction density, with specific area proportion controls (first peak area proportion 20-80%, second peak area proportion 20-80%). This segmentation allows simultaneous optimization of both contradictory parameters.
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 patent uses local quality to ensure that regions with large particles (providing high compaction density) are balanced by regions with small particles (providing high gram capacity). The small particles contribute more surface area per unit volume for lithium-ion insertion/extraction, maintaining high gram capacity while large particles increase overall electrode density. The controlled area proportions ensure both qualities coexist.
Solution Approach 2:
The patent creates a composite particle size structure within the electrode material layer. By combining particles of two different size ranges in specific proportions, the electrode achieves properties that neither single-size population could provide alone: high compaction density from large particles and high gram capacity from small particles. This composite approach resolves the contradiction between these two parameters.
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 limited
Solution Approach 1:
The patent applies parameter changes by modifying the particle size distribution parameters from a single-mode distribution to a bimodal distribution. Specific parameters are controlled: Dv10 (10th percentile volume diameter), Dv50 (median volume diameter), and Dv90 (90th percentile volume diameter) are all specified within certain ranges. The area proportions of the two peaks are also controlled (20-80% each). These parameter specifications provide clear manufacturing targets while achieving improved kinetic performance.
Solution Approach 2:
The patent introduces dynamics into the particle size distribution by creating a flexible bimodal system where the relative proportions of small and large particles can be adjusted within specified ranges (area proportions of 20-80% for each peak). This allows optimization for different application requirements while maintaining the fundamental bimodal structure. The dynamic adjustment capability balances manufacturing simplicity with performance optimization.
Data Source
AI summary
Disclosed 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 having 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.