Cyclic Carbonate Electrolytes for Stable SEI and CEI in Si Batteries
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Solution Overview
Problem
Lithium-ion batteries with silicon-based anodes and high-voltage cathodes face challenges such as volumetric expansion, unstable solid electrolyte interphase (SEI) layer formation, oxidative instability, and poor cycle life due to electrolyte decomposition, leading to reduced energy density and safety concerns.
Innovation Solution
Development of electrolyte additives that form a stable, electronically insulating yet ionically conductive SEI layer on silicon anodes and a protective cathode electrolyte interphase (CEI) layer on high-voltage cathodes, using cyclic carbonate additives to enhance thermal stability and reduce flammability.
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 occurs during lithiation
Solution Approach 1:
The patent employs a flexible polymer coating layer that conformally coats the silicon anode particles. This flexible film accommodates the volumetric expansion and contraction of silicon during lithiation and delithiation cycles, preventing particle disintegration while maintaining structural integrity. The coating acts as a dynamic buffer that moves with the expanding silicon core, solving the volume expansion problem.
Solution Approach 2:
The patent creates a composite structure consisting of silicon particles embedded in a polymer matrix. This composite material combines the high capacity of silicon with the structural stability and flexibility of the polymer coating. The composite design allows the system to benefit from silicon's high capacity while the polymer matrix provides mechanical stability during volume changes.
2Quantity of substance
If conventional electrolytes are used with silicon anodes, then initial capacity is achieved, but SEI layer instability occurs leading to continuous electrolyte decomposition
Solution Approach 1:
The patent introduces a polymer coating as an intermediary layer between the silicon anode and the liquid electrolyte. This intermediary SEI layer acts as a protective barrier that prevents direct contact between the electrolyte and silicon surface, eliminating continuous electrolyte decomposition. The polymer coating is specifically designed to be ionically conductive while providing chemical stability.
Solution Approach 2:
The patent modifies the chemical composition and physical properties of the SEI layer by using polymer-coated silicon particles instead of bare silicon. This parameter change transforms the SEI layer from an unstable, continuously decomposing interface to a stable, protective barrier with controlled ion transport properties, significantly improving cycle life.
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
Solution Approach 1:
The patent introduces a protective coating on the cathode surface as an intermediary layer between the high-voltage cathode material and the liquid electrolyte. This coating acts as a barrier that prevents direct oxidative reactions between the electrolyte and cathode surface, enabling stable operation at high voltages beyond 4.5 V while maintaining capacity.
4Quantity of substance
If silicon anodes are used to improve energy density, then capacity is improved, but cycle life is reduced due to particle disintegration
Solution Approach 1:
The patent employs a flexible polymer coating that conformally covers the silicon particles, providing mechanical protection during repeated expansion and contraction cycles. This flexible shell maintains particle integrity over thousands of cycles, preventing disintegration and maintaining both capacity and cycle life simultaneously.
Solution Approach 2:
The patent creates a composite material system where silicon particles are embedded in a polymer matrix, combining the high capacity of silicon with the structural stability and flexibility of the polymer. This composite structure ensures long-term mechanical integrity during cycling, dramatically improving cycle life while maintaining high capacity.
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
Improves the electrochemical performance and safety of silicon-based lithium-ion batteries by stabilizing the SEI and CEI layers, preventing volume expansion, and enhancing thermal stability, thereby increasing cycle life 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 use in energy storage devices, comprising cyclic carbonate compounds.