Li-Ion Electrolyte Additives for High-Temperature SEI Stability
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Solution Overview
Problem
Lithium-ion batteries face challenges in high-temperature cycle performance and storage due to electrolyte decomposition and solid-electrolyte interface (SEI) film instability, leading to reduced capacity and increased thickness growth.
Innovation Solution
An electrolyte comprising specific compounds (Formulas I, II, III, and IV) with additives like lithium difluorophosphate and fluoroethylene carbonate, which stabilize the anode interface, protect the cathode, and reduce solvent decomposition, along with an optimized anode active material layer structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional electrolytes are used in lithium-ion batteries, then the batteries can operate at high voltage and have high energy density, but the electrolyte decomposes and SEI film becomes unstable at high temperatures, leading to reduced capacity and increased thickness growth
Solution Approach 1:
The patent introduces a mediator substance (specifically, a compound containing fluorinated cyclic carbonate and chain carbonate) that acts as an intermediary between the electrolyte and the electrode interfaces. This mediator forms a stable protective layer that prevents direct contact between the unstable conventional electrolyte and the electrodes, thereby reducing electrolyte decomposition and stabilizing the SEI film at high temperatures without compromising the high voltage operation
Solution Approach 2:
The patent modifies the chemical composition parameters of the electrolyte by incorporating specific fluorinated cyclic carbonate and chain carbonate compounds in optimized ratios. This parameter change alters the electrolyte's decomposition characteristics and SEI-forming properties, enabling it to maintain stability at high temperatures while preserving the high energy density performance
2Reliability
If conventional electrolytes are used in lithium-ion batteries, then the batteries can achieve high energy density, but the SEI film thickness increases during storage, leading to capacity loss
Solution Approach 1:
The fluorinated cyclic carbonate and chain carbonate compound acts as a mediator that forms a thin, stable SEI film during initial cycles. This mediator-derived SEI film has lower ionic resistance and prevents continuous electrolyte decomposition during storage, thereby maintaining capacity retention without excessive thickness growth
Solution Approach 2:
The patent employs a small amount of sacrificial additive (fluorinated cyclic carbonate and chain carbonate) that decomposes preferentially to form a stable protective SEI film. This disposable-like approach uses a small concentration of the additive (0.01-10 wt%) that consumes itself to create a long-lasting stable interface, preventing further electrolyte decomposition during storage
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
Significantly improves high-temperature interval cycle performance and storage capacity retention by reducing SEI film consumption and electrolyte decomposition, maintaining battery performance and structural integrity.
Implementation Method 1
stabilize the anode interface, protect the cathode, and reduce solvent decomposition
Implementation Method 2
stabilize the anode interface, protect the cathode
Implementation Method 3
reduce solvent decomposition
Data Source
AI summary
An electrolyte includes at least one of a compound of Formula I, a compound of Formula II or a compound of Formula III; and a compound of Formula IV; where,R11, R12, R13, R21, R22, R31, R32, R33 and R34 are independently selected from H, halo, cyano, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, and substituted or unsubstituted C6-C12 aryl; R41 and R44 are independently selected from H, F, cyano, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C6-C12 aryl, Ra—(O—Rb), or (O—Rb); and R42 and R43 are independently selected from Rc—(O—Rd) or (O—Rd). Rb is selected from substituted or unsubstituted C1-C4 alkyl; Ra, Rc and Rd are independently selected from substituted or unsubstituted C1-C4 alkylene, C2-C5 alkenylene, or C6-C12 aryl.