Silicon Negative Electrode Binder Copolymer for Volume Expansion Control
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Solution Overview
Problem
Silicon particles used as negative electrode active material in batteries experience excessive volume expansion during charging and discharging, leading to increased resistance and reduced lifespan due to disconnection of the conductive path.
Innovation Solution
A negative electrode configuration with a current collector and a negative electrode active material layer containing silicon particles, carbon black, and a binder composed of a copolymer derived from poly(vinylalcohol) and ionized and substituted acrylate, where the binder is present in the range of 18 wt % to 22 wt %, maintaining the conductive path and stabilizing the electrode structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon particles are used as negative electrode active material to improve capacity, then battery capacity is improved, but volume expansion occurs during charging and discharging leading to increased resistance
Solution Approach 1:
The patent changes the chemical composition parameters of the binder by using a copolymer with specific functional groups (carboxyl, hydroxyl, and/or ammonium groups) and controlling its molecular weight and composition ratio. This parameter optimization allows the binder to effectively suppress silicon particle expansion while maintaining conductivity, resolving the contradiction between capacity improvement and resistance increase.
Solution Approach 2:
The patent employs a composite binder system comprising a copolymer with specific functional groups combined with silicon particles and carbon black. This composite material approach creates a synergistic effect where the functional groups in the copolymer interact with silicon particles to suppress expansion, while carbon black maintains conductive pathways, thereby resolving the contradiction between high capacity and low resistance.
2Quantity of substance
If silicon particles expand during charging and discharging, then capacity is improved, but the conductive path disconnects leading to increased resistance
Solution Approach 1:
The patent introduces the copolymer binder with functional groups as an intermediary substance between silicon particles and carbon black. This intermediary binds to silicon particles and suppresses their expansion, thereby preventing disconnection of the conductive path formed by carbon black. The binder acts as a mediator that maintains structural integrity while allowing capacity improvement through silicon utilization.
3Strength
If conventional binders like CMC or SBR are used to complement adhesion, then some adhesion problems are solved, but the effect is not significant enough to suppress volume expansion
Solution Approach 1:
The patent fundamentally changes the binder parameters by selecting a copolymer with specific functional groups (carboxyl, hydroxyl, and/or ammonium groups) and optimized molecular weight (100,000-500,000). This parameter optimization provides both strong adhesion through functional group interactions and effective volume expansion suppression through molecular chain flexibility and binding strength, overcoming the limitations of conventional binders.
4Reliability
If a carbon coating layer is formed on silicon particles to control volume expansion, then expansion is suppressed, but capacity is reduced due to reduced silicon content
Solution Approach 1:
The patent uses the copolymer binder as an intermediary that suppresses silicon particle expansion from the outside without requiring a carbon coating layer on the silicon surface. This approach maintains high silicon content (and thus high capacity) while the binder's functional groups interact with silicon particles to control their expansion behavior, avoiding the capacity loss associated with carbon coating.
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 effectively suppresses the increase in battery resistance and improves the lifespan of the negative electrode by maintaining the conductive path and stabilizing the electrode structure despite silicon particle expansion, enhancing capacity retention and battery performance.
Implementation Method 1
the binder includes a copolymer containing a unit derived from a poly(vinylalcohol) (PVA) and a unit derived from an ionized and substituted acrylate
Implementation Method 2
carbon black, and a binder... maintaining the conductive path
Data Source
AI summary
The present invention relates to a negative electrode including a current collector and a negative electrode active material layer disposed on the current collector, wherein the negative electrode active material layer includes a negative electrode active material, carbon black, and a binder, wherein the negative electrode active material includes silicon particles, and the binder includes a copolymer containing a unit derived from a poly(vinylalcohol) (PVA) and a unit derived from an ionized and substituted acrylate, the binder being included in the negative electrode active material layer in an amount of 18 wt % to 22 wt %.