Layered Silicon-Graphite Negative Electrode for Swelling Control
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Solution Overview
Problem
Silicon-based negative electrode materials in lithium-ion batteries experience significant volume swelling during charge and discharge cycles, leading to structural instability, electrolyte penetration, and reduced cycling performance.
Innovation Solution
A negative electrode plate design featuring multiple active material layers, where the second negative electrode active material layer, composed of a silicon-based material and graphite, is strategically positioned between the current collector and the first negative electrode active material layer, with controlled particle size distributions and adhesion mechanisms to mitigate swelling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based material is used as negative electrode active material, then the reversible capacity and energy density are improved, but the volume swelling exceeds 100% during charge and discharge cycles, destroying structural stability and integrity
Solution Approach 1:
The patent applies the nesting principle by placing silicon-based material particles inside the porous structure of graphite material. The silicon particles are nested within the graphite matrix, allowing the graphite to constrain the silicon during volume expansion while maintaining electrical contact. This nested structure enables the silicon to achieve its high capacity potential without suffering from the detrimental effects of uncontrolled swelling.
Solution Approach 2:
The patent employs composite materials by combining graphite material and silicon-based material in a specific configuration. The graphite-silicon composite structure leverages the dimensional stability of graphite to accommodate the volume changes of silicon during lithium insertion and extraction. This composite approach allows the negative electrode to achieve high reversible capacity from the silicon while maintaining structural integrity through the graphite framework.
2Quantity of substance
If silicon-based material is used, then energy density is improved, but large volume swelling damages solid electrolyte interphase (SEI) and triggers unstable reactions such as electrolyte decomposition and repeated SEI formation
Solution Approach 1:
The nesting of silicon particles within the graphite porous structure provides a protective effect. The graphite matrix acts as a physical constraint that limits the amplitude of silicon volume changes, thereby protecting the SEI layer from damage. This nested configuration reduces the frequency and intensity of SEI breakdown and reformation cycles, improving the reliability and cycling performance of the battery.
Solution Approach 2:
The graphite-silicon composite material combines the advantages of both components: graphite provides structural stability and SEI protection, while silicon contributes high capacity. This composite material approach enables the battery to achieve high energy density without sacrificing cycling reliability, as the graphite component mitigates the harmful effects of silicon swelling on the electrolyte and SEI.
3Strength
If graphite material with larger particle size is used to bind silicon-based material, then adhesion is improved, but Li+ diffusion is hindered
Solution Approach 1:
The patent applies local quality by using graphite material with specific particle size characteristics (Dv50 of 12-30 μm) that provides optimal local properties for both adhesion and ion diffusion. The graphite particles are sized to create a porous structure that offers sufficient surface area for binding silicon while maintaining adequate pore dimensions for lithium ion transport. This local optimization of particle size achieves a balance between mechanical adhesion and ionic conductivity.
Solution Approach 2:
The patent utilizes the porous structure of graphite material to simultaneously achieve good adhesion and fast lithium ion diffusion. The porous network provides a three-dimensional framework that mechanically binds silicon particles while the interconnected pores serve as diffusion pathways for lithium ions. This porous architecture resolves the contradiction between requiring sufficient graphite content for adhesion and maintaining open structures for ion transport.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively addresses the cycling swelling issue, enhancing the cycling capacity retention rate of electrochemical apparatuses and maintaining excellent adhesion and kinetic performance.
Implementation Method 1
the silicon-based material with a small particle size adsorbs a binder, and pores formed by graphite particles are filled with the silicon-based material adsorbed with the binder with a small particle size, offering better adhesion, enhancing the adhesion force of electrode plates
Data Source
AI summary
A negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer. The second negative electrode active material layer is located between the current collector and the first negative electrode active material layer. The first negative electrode active material layer includes a first graphite material, and Dv50 of the first graphite material is denoted as Dv150, and 10 μm≤Dv150≤16 μm. The second negative electrode active material layer includes a second graphite material and a silicon-based material, Dv50 of the second graphite material is denoted as Dv250, and 12 μm≤Dv250≤30 μm, and Dv50 of the silicon-based material is denoted as Dv350, and 6 μm≤Dv350≤10 μm.