Fluorinated Cyclic Electrolyte Additives for Silicon Anodes
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Solution Overview
Problem
Lithium-ion batteries with silicon-based anodes and high-voltage cathodes face challenges such as unstable solid electrolyte interphase layers, oxidative instability, and poor cycling life due to volumetric expansion and transition metal ion dissolution, which limit their energy density and safety.
Innovation Solution
The development of fluorinated cyclic electrolyte additives forms stable, electronically insulating but ionically conducting solid electrolyte interphase layers on silicon anodes and cathodes, enhancing electrochemical stability and thermal safety by reducing electrolyte reactions and transition metal ion dissolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based anodes are used to increase energy density, then capacity is improved, but volumetric expansion during lithiation causes disintegration and reduces cycling life
Solution Approach 1:
A flexible coating layer comprising fluorinated cyclic carbonate and fluorinated cyclic carboxylate is formed on the silicon-based anode surface. This thin film layer accommodates the volumetric expansion (>300%) during lithiation while maintaining structural integrity, preventing disintegration of the active material and preserving electrical conduction paths throughout cycling.
Solution Approach 2:
The anode structure combines silicon-based active material with a composite coating layer containing fluorinated cyclic carbonate and fluorinated cyclic carboxylate. This composite structure provides both high capacity from silicon and enhanced cycling stability from the protective fluorinated coating that resists electrolyte decomposition.
2Quantity of substance
If conventional electrolytes are used with silicon anodes, then initial capacity is achieved, but unstable solid electrolyte interphase forms leading to continuous electrolyte reduction and capacity loss
Solution Approach 1:
The electrolyte composition is modified by introducing fluorinated cyclic carbonate and fluorinated cyclic carboxylate additives. These compounds change the chemical parameters of the electrolyte system, enabling formation of a stable solid electrolyte interphase that prevents continuous reduction reactions. The fluorinated additives alter the reduction potential and reaction kinetics at the silicon anode interface.
Solution Approach 2:
The fluorinated cyclic carbonate and fluorinated cyclic carboxylate act as intermediary substances that mediate between the silicon anode and the bulk electrolyte. They form a protective intermediate layer that allows initial lithium insertion while blocking subsequent harmful reduction reactions, thereby preserving capacity retention over cycling.
3Quantity of substance
If high-voltage cathodes are used to increase energy density, then capacity is improved, but oxidative instability occurs beyond 4.5 V leading to accelerated decay
Solution Approach 1:
The electrolyte system parameters are changed by adding fluorinated cyclic carbonate and fluorinated cyclic carboxylate, which increase the oxidative stability threshold. These additives modify the electrochemical window of the electrolyte, enabling stable operation at high voltages beyond 4.5 V without accelerated decomposition or cathode material degradation.
4Quantity of substance
If conventional electrolytes are used with high-voltage cathodes, then initial performance is achieved, but transition metal ion dissolution occurs leading to poor cycling stability
Solution Approach 1:
The fluorinated cyclic carbonate and fluorinated cyclic carboxylate serve as intermediary protective agents between the high-voltage cathode and the bulk electrolyte. They form a stable interface layer that prevents direct contact and dissolution of transition metal ions into the electrolyte, thereby maintaining cycling stability while preserving initial performance characteristics.
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
These additives improve the cycle life and safety of silicon-based lithium-ion batteries by stabilizing the electrolyte interface, reducing flammability, and increasing thermal stability, leading to enhanced electrochemical performance and safety.
Implementation Method 1
an unstable solid electrolyte interphase (SEI) layer can develop on the surface of the cycled anodes, and leads to an endless exposure of Si particle surfaces to the liquid electrolyte. This results in an irreversible capacity loss at each cycle due to the reduction at the low potential where the liquid electrolyte reacts with the exposed surface of the Si anode
Implementation Method 2
oxidative instability of the conventional non-aqueous electrolyte takes place at voltages beyond 4.5 V, which can lead to accelerated decay of cycling performance
Data Source
AI summary
Electrolytes and electrolyte additives for energy storage devices comprising fluorinated cyclic compounds.