Silicon Anode Copolymer Binders for Stable Lithium-Ion Cycling
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Solution Overview
Problem
Lithium ion cells with silicon-based negative electrodes face challenges due to high irreversible capacity loss and poor cycling stability caused by structural changes and large volume expansions during lithium intercalation/alloying, leading to decreased cycling efficiency.
Innovation Solution
A negative electrode comprising a silicon-based active material, nanoscale conductive carbon, and a polymer binder composed of a copolymer of acrylamide and acrylate salt, which provides improved adhesion and cohesion, maintaining electrode integrity and enabling stable cycling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon based active materials are used in negative electrodes, then energy density is increased, but cycling stability deteriorates due to structural changes and volume expansions
Solution Approach 1:
The silicon based active material is divided into nanoscale particles (average diameter 5-50 nm), which segments the material to reduce individual particle volume expansion stress and prevent catastrophic structural failure during cycling
Solution Approach 2:
A water-based polymer binder system comprising carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) is introduced as an intermediary between the silicon particles and current collector, providing mechanical support and maintaining electrode integrity during volume changes
Solution Approach 3:
The negative electrode is formulated as a composite material system containing silicon nanoparticles, conductive carbon, CMC binder, and SBR binder, where each component addresses specific aspects of the cycling stability problem while maintaining high capacity
2Ease of manufacture
If conventional organic-based binders are used, then electrode manufacturing is simplified, but adhesion and cohesion properties deteriorate with silicon-based active materials
Solution Approach 1:
The binder system transitions from conventional organic-based binders to a water-based polymer system, changing the solvent parameter to enable better wetting of silicon surfaces and improved adhesion while maintaining ease of manufacturing through aqueous processing
Solution Approach 2:
The binder system itself is a composite of two different polymers (CMC and SBR) with complementary properties, where CMC provides adhesion to silicon particles and SBR provides cohesion and flexibility to accommodate volume changes
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 copolymer binder enhances the cycling stability of silicon-based electrodes, allowing for over 800 cycles with less than 20% capacity loss, suitable for both consumer electronics and vehicle applications.
Implementation Method 1
The negative electrode can be a component of a negative electrode structure that comprises a metal foil current collector and the negative electrode on the current collector with the negative electrode structure having a 180 degree peel adhesion with a force of at least about 6 pound-force/meter
Implementation Method 2
a cohesion corresponding to maintenance of electrode integrity when bent around a mandrel with a diameter of 6 mm
Implementation Method 3
structural changes and anomalously large volume expansions, especially for silicon, that are associated with lithium intercalation/alloying
Implementation Method 4
structural changes and anomalously large volume expansions, especially for silicon, that are associated with lithium intercalation/alloying
Data Source
AI summary
Polymer binders for negative electrodes with silicon based active materials are described based on poly(acrylamide-co-acrylate salts). Lithium ion batteries incorporating electrodes formed with the binders achieve longer cycling with suitable performance. Mechanical properties associated with each of the moieties of the copolymers are studied to guide polymer selection.