Si-Based Negative Electrode Binder for Lithium Battery Volume Expansion
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Solution Overview
Problem
Rechargeable lithium batteries face challenges with the cycle life and volume expansion of negative electrodes, particularly when using silicon-based active materials, which require improved stability and efficiency.
Innovation Solution
A negative electrode for rechargeable lithium batteries is developed, comprising a Si-based negative active material layer with a polymer binder and a current collector, where the binder is a copolymer of specific repeating units, and the Si-based material includes a composite of silicon and carbon with porosity to absorb expansion, along with a carbon-based active material for enhanced adherence and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si-based negative active material is used to increase capacity, then battery capacity is improved, but volume expansion occurs during charging and discharging
Solution Approach 1:
A polymer binder comprising a repeating unit of formula (1) or (2) is used to bind the Si-based negative active material. The polymer binder forms a flexible matrix that can accommodate the volume expansion of Si during lithiation while maintaining electrode integrity, preventing the electrode from breaking apart despite the significant volume changes.
Solution Approach 2:
The negative active material layer is formed as a composite comprising Si-based negative active material particles dispersed in a polymer binder matrix. This composite structure allows the Si particles to maintain their high capacity while the polymer binder provides mechanical stability and accommodates volume changes, resolving the contradiction between capacity and volume stability.
2Quantity of substance
If Si-based negative active material is used to increase capacity, then battery capacity is improved, but cycle life deteriorates due to electrode degradation
Solution Approach 1:
The polymer binder forms a flexible binding matrix that accommodates the volume expansion and contraction of Si during charge-discharge cycles. This flexible matrix prevents the electrode from breaking apart, maintaining electrode integrity over multiple cycles and thereby improving cycle life while preserving the high capacity of Si-based materials.
Solution Approach 2:
The invention changes the chemical composition parameters of the binder by using a polymer with specific repeating units of formula (1) or (2) containing oxygen-containing groups. These compositional changes enhance the binder's ability to accommodate volume changes and maintain adhesion, directly improving cycle life while maintaining high capacity.
3Stability of the object's composition
If polymer binder content is increased to suppress volume expansion, then electrode integrity is improved, but initial charge and discharge efficiency decreases
Solution Approach 1:
The invention optimizes the chemical composition parameters of the binder by using a polymer with specific repeating units of formula (1) or (2). This compositional change allows for reduced binder content (1-10 wt%) while maintaining sufficient electrode integrity and volume expansion suppression, thereby preserving high initial charge and discharge efficiency that would otherwise be lost with higher binder content.
Solution Approach 2:
The negative active material layer is designed as an optimized composite with Si-based material particles dispersed in a minimal amount of polymer binder (1-10 wt%). This composite structure maximizes the active material content for high efficiency while the polymer provides just enough binding to maintain integrity, achieving the optimal balance between electrode stability and charge-discharge efficiency.
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 the cycle life and initial charge and discharge efficiency of the lithium battery by suppressing volume expansion and maintaining electrode integrity through appropriate binder content and structure, leading to enhanced battery performance.
Implementation Method 1
a polymer binder including a repeating unit represented by the following Chemical Formula 1 or the following Chemical Formula 2
Implementation Method 2
a composite of Si and C may include a crystalline carbon core including pores therein, an amorphous carbon shell formed on the surface of the core, and Si nano particles dispersed in the pore and amorphous carbon present inside the pore
Implementation Method 3
heat-treating the current collector applied with the negative active material composition at 80° C. to 160° C.
Data Source
AI summary
A negative electrode for a rechargeable lithium battery, including a negative active material layer including a polymer binder including a repeating unit represented by the following Chemical Formula 1 or the following Chemical Formula 2 and a Si-based negative active material; and a current collector supporting the negative active material layer, is provided:wherein in Chemical Formulae 1 and 2, R1 and R2 are the same or different and hydrogen, OH or OOH.