Silicon Negative Electrode Primer Layer for Volume Expansion
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Solution Overview
Problem
Lithium secondary batteries face limitations in increasing energy density due to the small capacity of graphite negative electrodes and the poor lifespan properties of silicon-based active materials, which experience volume expansion and reduced adhesive strength during charging and discharging.
Innovation Solution
A negative electrode manufacturing method involving a primer layer of styrene butadiene rubber and a mixture layer with a silicon-based active material and a polyacrylic acid-based binder, where the binder includes 40 to 90 mol% acrylic acid-derived structural units and the styrene butadiene rubber includes 10 to 95 mol% butadiene-derived structural units, applied before drying to enhance adhesive strength and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode active material is used to increase capacity, then energy density is improved, but volume expansion occurs during charging and discharging
Solution Approach 1:
The patent applies a flexible polymer coating layer comprising styrene-butadiene rubber and polyacrylic acid onto the silicon-based negative electrode active material. This flexible film accommodates the volume expansion and contraction of silicon during lithium insertion and extraction, preventing structural degradation while maintaining electrical contact and adhesive strength throughout charge-discharge cycles.
Solution Approach 2:
The patent creates a composite structure by combining silicon-based negative electrode active material with a polymer coating layer consisting of styrene-butadiene rubber and polyacrylic acid. This composite material integrates the high capacity of silicon with the mechanical flexibility and adhesive properties of the polymer, resolving the contradiction between capacity enhancement and volume stability.
2Quantity of substance
If silicon-based negative electrode active material is used to increase capacity, then energy density is improved, but adhesive strength reduces during charging and discharging
Solution Approach 1:
The flexible polymer coating layer maintains intimate contact with the silicon particles during volume changes, preventing particle detachment from the current collector and maintaining adhesive strength. The coating acts as a protective shell that flexes with the underlying silicon without losing bonding.
Solution Approach 2:
The composite of silicon with styrene-butadiene rubber and polyacrylic acid creates a material system where the polymer components provide adhesive functionality. The polyacrylic acid specifically contributes to adhesive strength through its polar carboxylic acid groups, while the styrene-butadiene rubber provides mechanical flexibility, together maintaining strong bonding despite silicon's volume changes.
3Quantity of substance
If silicon-based negative electrode active material is used to increase capacity, then energy density is improved, but conductivity reduces in the electrode
Solution Approach 1:
The polymer coating layer is designed to be electrically conductive or to maintain electrical contact pathways. The styrene-butadiene rubber component provides a flexible conductive network that accommodates volume changes while preserving electron transport pathways, preventing insulation that would occur with non-conductive coatings.
Solution Approach 2:
The composite material system incorporates conductive components within the polymer coating to maintain electrical conductivity. The combination of styrene-butadiene rubber and polyacrylic acid creates a matrix that supports electron transport while accommodating silicon's volumetric changes, preventing conductivity loss.
4Stability of the object's composition
If graphite is used as negative electrode active material, then electrode stability is maintained, but capacity per unit mass is limited to 372 mAh/g
Solution Approach 1:
The flexible polymer coating enables silicon to achieve high capacity by protecting it from degradation during volume expansion. This coating allows silicon's superior capacity (exceeding graphite's 372 mAh/g) to be realized while maintaining the structural stability needed for long-term operation, effectively combining graphite's stability advantage with silicon's capacity advantage.
Solution Approach 2:
The patent creates a composite negative electrode material that combines silicon-based active material with a polymer coating system. This composite achieves capacity exceeding graphite's limitation by utilizing silicon's higher theoretical capacity while the polymer matrix provides the structural stability and adhesive strength that graphite inherently possesses, thereby overcoming graphite's capacity ceiling.
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 approach significantly improves the lifespan properties of the secondary battery by alleviating expansion and contraction of the silicon-based negative electrode active material, leading to enhanced capacity retention and reduced electrode brittleness.
Implementation Method 1
a polyacrylic acid-based binder onto the first slurry
Implementation Method 2
styrene butadiene rubber may include 10 to 95 mol% of a butadiene-derived structural unit
Data Source
Figure 1
AI summary
A method of manufacturing a negative electrode includes styrene butadiene rubber on at least one surface of a negative electrode current collector, applying a second slurry including a negative electrode active material and a polyacrylic acid-based binder onto the first slurry, and drying and rolling the negative electrode current collector to which the first slurry and the second slurry are applied. The negative electrode active material includes a silicon-based negative electrode active material. According to the present disclosure, expansion and contraction of a silicon-based negative electrode active material during charging and discharging may be alleviated, and electrode flexibility may be improved, resulting in a significant improvement in lifespan properties of a secondary battery.