Silicon Negative Electrode Composition for Volume Expansion Control
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Solution Overview
Problem
Lithium secondary batteries with silicon-based negative electrodes face challenges in maintaining lifespan and output properties due to volume expansion and contraction, leading to electrical shorts and reduced conductivity, which existing binders fail to adequately address.
Innovation Solution
A negative electrode composition incorporating a silicon-based active material, graphite as a first conductive material, single-walled carbon nanotubes as a second conductive material, and a binder comprising cellulose-based and rubber-based compounds, optimized in specific weight ratios and amounts to enhance tensile strength and electrolyte solution wetting, maintaining a conductive network and controlling volume expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a silicon-based active material is used together with a binder including styrene butadien rubber and carboxymethyl cellulose, then the negative electrode can accommodate silicon-based active material, but the binder does not have high tensile strength and cannot sufficiently suppress the volume expansion of the silicon-based active material
Solution Approach 1:
The patent uses a composite binder system comprising polyvinyl alcohol, polyacrylic acid, and carboxymethyl cellulose in specific weight ratios (5:4:1 to 7:3:2). This composite approach combines the high tensile strength of polyvinyl alcohol and polyacrylic acid with the excellent wetting properties of carboxymethyl cellulose, achieving both mechanical strength and effective volume expansion suppression of the silicon-based active material.
2Reliability
If a silicon-based active material is used together with a binder such as polyvinyl alcohol, polyacrylic acid, and the like having high tensile strength, then the binder has high tensile strength, but the binder has poor wetting and degrades the conductivity and increases the resistance of the active material
Solution Approach 1:
The patent employs a composite binder system where carboxymethyl cellulose (providing excellent wetting properties) is combined with polyvinyl alcohol and polyacrylic acid (providing high tensile strength). The specific weight ratio range (5:4:1 to 7:3:2) optimizes the balance between wetting capability and mechanical strength, ensuring both low resistance and effective volume expansion control.
Solution Approach 2:
The binder system provides different functional properties in different aspects: polyvinyl alcohol and polyacrylic acid contribute primarily to tensile strength and structural integrity, while carboxnymethyl cellulose contributes primarily to wetting properties and conductivity. This functional differentiation within the composite binder resolves the contradiction between strength and wetting.
3Duration of action of stationary object
If a binder with high tensile strength is used to suppress volume expansion, then the lifespan properties improve, but the wetting properties deteriorate and output properties are reduced
Solution Approach 1:
The composite binder system achieves both long lifespan and high output by combining materials with complementary properties. The polyvinyl alcohol and polyacrylic acid provide the structural framework for lifespan durability, while carboxymethyl cellulose ensures excellent electrolyte wetting for high conductivity and power output. The optimized weight ratios ensure both functions operate at optimal levels simultaneously.
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
The solution significantly improves both lifespan and output properties of the negative electrode by maintaining a conductive network and controlling volume expansion, leading to enhanced performance and stability in lithium secondary batteries.
Implementation Method 1
the second conductive material and the binder bind to one another
Implementation Method 2
the binder such as polyvinyl alcohol, polyacrylic acid, and the like has poor wetting
Data Source
AI summary
The present invention relates to a negative electrode including a negative electrode current collector, and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer includes a silicon-based active material, a first conductive material including graphite, a second conductive material including a single-walled carbon nanotube, and a binder, wherein the binder includes a cellulose-based compound and a rubber-based compound, the first conductive material is included in the negative electrode active material layer in an amount of 15 wt % to 25 wt %, the second conductive material is included in the negative electrode active material layer in an amount of 0.15 wt % to 2.5 wt %, and the second conductive material and the binder are included in the negative electrode active material layer at a weight ratio of 1.5:99.5 to 20.0:80.0.