Multilayer Graphite Anode Structure for Fast-Charging Porosity Retention
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Solution Overview
Problem
The reduction of pores in anode electrodes during the rolling process for secondary batteries leads to increased resistance and degraded battery performance, particularly when using graphite secondary particles as anode active material, which results in reduced lithium ion movement paths and impaired fast charging capabilities.
Innovation Solution
A multilayer anode structure is implemented, with a first anode mixture layer on the current collector and a second anode mixture layer on the surface, where the second layer contains a higher content of graphite primary particles than the first layer, and both layers include graphite secondary particles, to minimize porosity reduction during rolling, thereby enhancing lithium ion movement and reducing internal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a rolling process is used to flatten the anode electrode, then the electrode surface is flattened and manufacturing efficiency is improved, but pores of the electrode are reduced and lithium ion movement paths are blocked
Solution Approach 1:
The anode electrode is divided into multiple layers with different compositions. The first layer (near current collector) contains mainly graphite secondary particles, while the second layer (surface layer) contains graphite secondary particles plus additional graphite primary particles. This segmentation allows different regions to serve different functions: the first layer provides structural integrity for rolling, while the second layer maintains porosity for lithium ion movement.
Solution Approach 2:
Different regions of the anode electrode are given different material compositions tailored to their specific functions. The inner layer near the current collector is optimized for mechanical stability during rolling, while the outer surface layer is optimized for maintaining pores and facilitating lithium ion diffusion. This local quality differentiation resolves the contradiction between flattening requirements and pore preservation.
2Quantity of substance
If graphite secondary particles are used as anode active material, then the anode capacity is improved, but deformation during rolling is high and pores are significantly reduced
Solution Approach 1:
The anode electrode uses a composite structure combining graphite secondary particles (for high capacity) with graphite primary particles (for low deformation). The secondary particles provide the desired high capacity, while the primary particles act as a deformable buffer that absorbs rolling pressure, preventing excessive deformation of the secondary particles and preserving pore structure.
3Manufacturing precision
If the anode surface is flattened during rolling, then manufacturing precision is improved, but resistance increases and fast charging characteristics deteriorate
Solution Approach 1:
The solution addresses the surface flatness issue by creating a layered structure where the surface layer (second layer) maintains higher porosity despite rolling. The flattening effect is concentrated in the inner layer, while the outer layer preserves its three-dimensional pore structure through the inclusion of primary particles, thus maintaining lithium ion pathways while achieving acceptable surface flatness for manufacturing.
Data Source
AI summary
An anode for a secondary battery includes a first anode mixture layer disposed on an anode current collector and a second anode mixture layer disposed on a surface of the anode, wherein the first and second anode mixture layers include a graphite-based anode active material of graphite secondary particles, at least the second anode mixture layer includes a graphite-based anode active material of graphite primary particles, and a content [A2] of graphite primary particles included in the second anode mixture layer is greater than a content [A1] of graphite primary particles included in the first anode mixture layer.