Phosphazene Electrolyte Additives for Silicon Anode SEI Stability
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Solution Overview
Problem
Lithium-ion batteries with silicon-based anodes and high-voltage cathodes face challenges such as large volumetric expansion, unstable solid electrolyte interphase layers, and poor cycling stability due to electrolyte decomposition and transition metal ion dissolution, leading to reduced energy density and safety concerns.
Innovation Solution
An electrolyte system comprising a phosphazene-based compound, a linear carbonate, and a cyclic carbonate with a Li-containing salt is used to stabilize the solid electrolyte interphase layer, reduce electrolyte reactions, and enhance thermal stability, thereby improving the cycling performance and safety of silicon-based anode batteries.
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 and cycling stability deteriorate
Solution Approach 1:
A fluorinated cyclic carbonate additive is introduced as an intermediary substance in the electrolyte system. This additive preferentially reacts with silicon anode surfaces to form a stable protective interface layer that mediates between the silicon and the bulk electrolyte, preventing harmful reactions while allowing lithium ion transport. The additive acts as a buffer that accommodates silicon expansion without compromising electrode integrity.
Solution Approach 2:
The electrolyte composition is modified by incorporating fluorinated cyclic carbonate compounds with specific molecular structures and fluorine substitutions. These parameter changes in the electrolyte chemistry alter the properties of the solid electrolyte interphase layer, making it more stable and less prone to decomposition during silicon anode cycling.
2Quantity of substance
If high-voltage cathodes are used to increase energy density, then capacity is improved, but electrolyte decomposition and transition metal ion dissolution worsen
Solution Approach 1:
The fluorinated cyclic carbonate additive serves as a protective intermediary at the cathode-electrolyte interface. It forms a stable protective layer that mediates interactions between the high-voltage cathode materials and the electrolyte, preventing direct contact and reducing decomposition reactions. This intermediary layer suppresses transition metal ion dissolution into the electrolyte.
Solution Approach 2:
The patent converts the potentially harmful high reactivity of high-voltage cathode materials into a benefit by using the fluorinated additive to form a highly stable protective interface. The additive's fluorine atoms create strong chemical bonds that form an exceptionally stable interface layer, turning the high energy density advantage into a sustainable long-term performance benefit rather than a source of degradation.
3Quantity of substance
If conventional electrolytes are used with silicon anodes, then initial capacity is achieved, but solid electrolyte interphase stability deteriorates
Solution Approach 1:
The electrolyte system undergoes parameter changes by incorporating fluorinated cyclic carbonate compounds. The fluorine substitution in the cyclic carbonate structure fundamentally alters the electrochemical properties of the solid electrolyte interphase layer formed during initial cycling. This results in an interface layer with enhanced stability, lower resistance, and better mechanical properties that can accommodate silicon volume changes.
Solution Approach 2:
The solid electrolyte interphase layer becomes a composite structure formed by the synergistic interaction of fluorinated cyclic carbonate additive and other electrolyte components. This composite interface layer combines the benefits of different materials, creating a multi-functional protective coating that provides both electrical insulation and mechanical flexibility to handle silicon expansion.
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 proposed electrolyte system improves the cycling stability and thermal stability of silicon-based anode batteries, reducing capacity fade and gas generation, and enhancing the overall performance and safety of lithium-ion batteries.
Implementation Method 1
An electrolyte system comprising a phosphazene-based compound, a linear carbonate, and a cyclic carbonate with a Li-containing salt is used to stabilize the solid electrolyte interphase layer, reduce electrolyte reactions
Implementation Method 2
enhance thermal stability, thereby improving the cycling performance and safety of silicon-based anode batteries
Data Source
AI summary
Electrolytes and electrolyte additives for energy storage devices comprising phosphazene based compounds are disclosed. The energy storage device comprises a first electrode and a second electrode, wherein at least one of the first electrode and the second electrode is a Si-based electrode, a separator between the first electrode and the second electrode, an electrolyte comprising at least two electrolyte co-solvents, wherein at least one electrolyte co-solvent comprises a phosphazene based compound.