Graphite Porosity Gradient in Li-Ion Anodes for Fast-Charge Cycle Life
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Solution Overview
Problem
Conventional non-aqueous electrolyte secondary batteries experience a decrease in battery capacity when subjected to rapid charge cycles due to the decomposition of the electrolyte solution and peeling of graphite particles from the current collector during high-rate charging.
Innovation Solution
The battery design incorporates graphite particles with specific porosities (5% or less for particles A and 8-20% for particles B) distributed unevenly in the negative electrode active material layer, with particles A predominantly on the outer surface and a non-aqueous electrolyte containing a carboxylic acid ester to enhance adhesion and permeability, thereby suppressing decomposition and peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If rapid charge cycle is performed at high rate to shorten charging time, then charging speed is improved, but battery capacity decreases due to electrolyte decomposition and graphite particle peeling
Solution Approach 1:
The patent applies local quality by creating a gradient structure where graphite particles with different internal porosities are distributed at different positions within the negative electrode active material layer. Specifically, particles A with 5% or less internal porosity are concentrated in the outer surface region, while particles B with 8% to 20% internal porosity are concentrated in the inner region near the current collector. This spatial differentiation of particle properties allows the outer surface to resist electrolyte decomposition while the inner region maintains adhesion, thereby resolving the contradiction between charging speed and battery capacity during rapid charge cycles.
2Productivity
If graphite particles with high internal porosity are used to improve electrolyte permeability, then ion transport is improved, but particle adhesion to current collector deteriorates
Solution Approach 1:
The patent resolves this contradiction by assigning different graphite particle types to different spatial zones within the negative electrode. Particles B with higher internal porosity (8% to 20%) are placed in the inner region near the current collector where they provide adequate electrolyte access while maintaining structural integrity and adhesion. Particles A with low internal porosity (5% or less) are placed in the outer surface region where they provide strong adhesion and resist peeling. This localized assignment of particle properties optimizes both ion transport efficiency and particle adhesion strength.
3Strength
If graphite particles with low internal porosity are used to improve adhesion, then particle stability is improved, but electrolyte permeability and ion transport deteriorate
Solution Approach 1:
The patent resolves this contradiction by creating a spatially differentiated structure where particles with low internal porosity (particles A, 5% or less) are concentrated in the outer surface region of the negative electrode active material layer, providing strong adhesion and resistance to peeling during rapid charge cycles. Meanwhile, particles with higher internal porosity (particles B, 8% to 20%) are concentrated in the inner region near the current collector, ensuring adequate electrolyte permeability and ion transport efficiency. This localized assignment allows each region to optimize for its specific functional requirements.
Data Source
AI summary
The purpose of the present disclosure is to provide a non-aqueous electrolyte secondary battery that can suppress reductions in rapid charge cycle characteristics. The non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure has a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode has a negative electrode collector and a negative electrode active material layer that is provided on the negative electrode collector. The negative electrode active material layer includes graphite particles A and graphite particles B as negative electrode active materials. The internal porosity of graphite particles A is no more than 5%, and the internal porosity of graphite particles B is 8%-20%. When the negative electrode active material layer is bisected in the thickness direction, there is a greater amount of graphite particles A in the outer surface-side half than in the negative electrode collector-side half.