Silicon Negative Electrode Layering for Lower Expansion and Longer Cycle Life
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Solution Overview
Problem
Silicon-based negative electrode materials in secondary batteries suffer from high expansion rates, poor cycle life, and poor high-temperature storage performance due to cracking and irreversible ion consumption during the lithium-ion reaction.
Innovation Solution
A negative electrode plate design featuring a dual-layer structure with a first region of spherical or spheroidal silicon-based material in direct contact with the electrolyte and a second region of smaller silicon-based material near the current collector, optimizing particle size, specific surface area, and silicon content to reduce expansion and enhance ion transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based material is used as negative electrode active material to improve energy density, then the capacity of the secondary battery is improved, but the expansion rate of the electrode plate increases and cycle life deteriorates
Solution Approach 1:
The negative electrode film layer is divided into two distinct regions: a first region containing spherical or spheroidal silicon-based material with larger particle size (5-20 μm) and a second region containing silicon-based material with smaller particle size (3-8 μm). This segmentation allows each region to fulfill different functions - the first region provides high capacity while the second region reduces expansion and improves cycle stability.
Solution Approach 2:
Different regions of the negative electrode film layer are assigned different material properties. The first region uses spherical or spheroidal silicon-based material with larger particle size and lower specific surface area to reduce cracking during cold pressing and minimize irreversible ion consumption. The second region uses smaller particle size material to enhance binder interaction and reduce expansion. This local differentiation of material properties resolves the contradiction between capacity and cycle life.
2Reliability
If silicon-based material with large particle size is used to reduce specific surface area and irreversible ion consumption, then storage performance is improved, but fast charging performance deteriorates
Solution Approach 1:
The negative electrode is segmented into two regions with different particle size distributions. The first region contains larger particle size silicon-based material (5-20 μm) optimized for storage performance by reducing specific surface area and irreversible ion consumption. The second region contains smaller particle size silicon-based material (3-8 μm) optimized for fast charging by providing shorter solid-phase ion transmission distances and greater binder interaction. This segmentation allows simultaneous optimization of both storage performance and fast charging capability.
3Manufacturing precision
If spherical or spheroidal silicon-based material is used in the first region to reduce cracking during cold pressing, then manufacturing precision is improved, but device complexity increases due to dual-layer structure
Solution Approach 1:
The spherical or spheroidal shape of silicon-based material is specifically applied to the first region that is in direct contact with the cold pressing roller. This local application of spherical morphology reduces cracking during cold pressing and maintains particle completeness where it is most needed. The dual-layer structure, while adding some complexity, is implemented in a targeted manner to achieve specific manufacturing benefits without unnecessarily complicating the entire electrode structure.
Data Source
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AI summary
A negative electrode sheet (10), a secondary battery (5), and an electric device. The negative electrode sheet (10) comprises a negative electrode current collector (101) and a negative electrode film layer (102) formed on at least one surface of the negative electrode current collector (101); the negative electrode film layer (102) has a first surface (102a) away from the negative electrode current collector (101) and a second surface (102b) opposite to the first surface (102a); the thickness of the negative electrode film layer (102) is denoted as H; the region within the thickness range from the first surface (102a) to 0.3 H of the negative electrode film layer (102) is denoted as a first region (1022) of the negative electrode film layer (102); the region within the thickness range from the second surface (102b) to 0.3 H of the negative electrode film layer (102) is denoted as a second region (1021) of the negative electrode film layer (102); the first region (1022) comprises a spherical or/and spheroid first silicon-based material. The negative electrode sheet (10) can reduce its own expansion rate and improve the cycle stability and storage performance of the battery.