Crosslinked PVDF Binder for Durable High-Loading Sulfur Electrodes
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Solution Overview
Problem
Lithium-sulfur batteries face challenges due to the insulating nature of sulfur and its discharge products, leading to low utilization and poor rate capability, as well as issues with solubility of polysulfides and mechanical degradation from volume expansion and contraction.
Innovation Solution
The development of electrodes with crosslinked polyvinylidene fluoride (PVDF) binders, which enhance ionic conductivity and mechanical compliance, thereby improving the cyclability and capacity retention of lithium-sulfur batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional PVDF binder is used in sulfur cathodes, then the electrode can be manufactured with simple processing, but the binder cannot withstand volume expansion and contraction during long duration cycling, leading to mechanical degradation
Solution Approach 1:
The binder undergoes chemical crosslinking transformation that changes its physical and chemical parameters, including increased molecular weight, enhanced mechanical strength, and improved elasticity. This allows the binder to withstand volume expansion and contraction during cycling while maintaining structural integrity and adhesion to the current collector
Solution Approach 2:
The crosslinked PVDF binder forms a composite network structure that combines the mechanical strength of crosslinked polymer chains with the flexibility needed to accommodate volume changes. This composite structure provides both the durability for long-term cycling and the simplicity of conventional binder application processes
2Quantity of substance
If sulfur cathodes use high active material loading to increase energy density, then volumetric and gravimetric density improve, but volume expansion and contraction cause severe mechanical degradation
Solution Approach 1:
Crosslinking transforms the PVDF binder from a thermoplastic material to a thermosetting network, changing its mechanical parameters to provide higher strength and elasticity. This enables the binder to accommodate the severe volume changes associated with high sulfur loading without mechanical failure
Solution Approach 2:
The crosslinked binder network is prepared in advance to provide mechanical cushioning and structural support before the electrode undergoes volume expansion and contraction during cycling. This pre-established network prevents mechanical degradation from occurring
3Reliability
If complex nano-architectured electrodes are synthesized to accommodate volume variation and improve cyclability, then cycling performance improves, but manufacturing complexity and cost increase significantly
Solution Approach 1:
The patent extracts and isolates the critical function of volume accommodation from the complex nano-architecture, assigning it to the crosslinked binder instead. This simplifies the overall electrode structure while maintaining the ability to withstand volume changes during cycling
Solution Approach 2:
The crosslinked PVDF binder acts as an intermediary material that mediates between the rigid current collector and the active sulfur material. It provides mechanical compliance and volume accommodation without requiring complex nano-architectured host materials
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 use of crosslinked PVDF binders in lithium-sulfur batteries results in improved cycle performance, increased capacity retention, and reduced mechanical degradation, enabling the batteries to withstand high voltages for a larger number of cycles.
Implementation Method 1
adding to the dissolved binder an aqueous solution comprising a metal hydroxide to form a crosslinked binder solution
Data Source
AI summary
In general, the present disclosure is directed to methods for producing an electrode having a crosslinked binder. In some embodiments the binder may comprise polyvinylidene fluoride. Said crosslinking may allow for higher loading capacities, increased ionic conductivity and/or durability. Further, electrodes and batteries comprising said electrodes which have crosslinked binders are described herein.