SP2 Anode Coating for Stable Salt-Derived SEI Formation
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Solution Overview
Problem
Lithium metal batteries, sodium metal batteries, and lithium-ion batteries with silicon anodes suffer from unstable and fragile solid electrolyte interphases (SEIs) that lead to capacity fading due to uncontrolled growth and cracking, resulting in poor cycling performance.
Innovation Solution
A salt-philic solvent-phobic (SP2) polymer coating is applied to the anodes, promoting the formation of a more robust salt-derived SEI by selectively transporting lithium or sodium salts over solvents, enhancing the stability and uniformity of the interface with the electrolyte.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional SEI is formed on lithium metal anodes, then the anode can operate in electrolyte, but the SEI becomes unstable and fragile leading to capacity fading
Solution Approach 1:
The patent introduces an artificial solid electrolyte interphase (SEI) coating as an intermediary layer between the lithium metal anode and the electrolyte. This artificial SEI acts as a mediator that prevents direct contact between the reactive lithium metal and the electrolyte, thereby stabilizing the interface and preventing the formation of unstable solvent-derived SEI layers that cause capacity fading.
Solution Approach 2:
The patent modifies the chemical composition and physical properties of the SEI layer by using specific polymer materials with controlled molecular weights, crosslinking densities, and chemical functionalities. These parameter changes transform the SEI from an unstable, fragile layer into a robust, stable protective interface that maintains its integrity during cycling.
2Quantity of substance
If the SEI grows uncontrolled, then more electrolyte components are consumed, but the SEI becomes thicker and more prone to cracking
Solution Approach 1:
The patent applies an artificial SEI coating before the battery enters service. This preliminary action pre-establishes a protective barrier that prevents uncontrolled electrolyte decomposition and SEI growth during initial cycling, thereby consuming less electrolyte and preventing the formation of thick, cracked SEI layers.
Solution Approach 2:
The patent uses thin film polymer coatings with flexible molecular structures that can accommodate volume changes of the lithium metal anode during cycling. These flexible thin films maintain mechanical integrity without becoming thick and brittle, preventing cracking while regulating electrolyte consumption.
3Reliability
If a polymer coating is applied to promote salt-derived SEI formation, then cycling performance improves, but the device complexity increases
Solution Approach 1:
The patent modifies only the local interface region between the anode and electrolyte by applying a thin polymer coating, rather than changing the entire anode structure. This localized modification promotes salt-derived SEI formation and improves cycling performance while minimizing the increase in overall device complexity.
Solution Approach 2:
The patent creates a composite structure combining polymer materials with specific chemical functionalities to form the artificial SEI. This composite material approach achieves improved cycling performance through controlled salt transport and SEI formation while maintaining relatively simple processing and structure.
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 SP2 polymer coating significantly improves cycling performance by increasing cycle life and capacity retention, demonstrating up to a 2.5-fold increase in cycle life with 80% capacity retention in full-cell cycling using various electrolytes.
Implementation Method 1
The SP2 polymer selectively transports salt over solvent and is configured to promote salt-derived SEI formation
Implementation Method 2
The first sidechains having salt affinity to promote salt transport
Implementation Method 3
the second sidechains being immiscible with polar aprotic solvents
Data Source
AI summary
A salt-philic solvent-phobic (SP2) polymer coating on a lithium anode, sodium anode, or a silicon anode selectively transports salt over solvent and is configured to promote salt-derived SEI formation on the anode. The SP2 coating can include a polymer backbone, a first side chain comprising a first moiety having salt affinity, and a second side chain comprising a second moiety immiscible with polar aprotic solvents.