Silicon Anode Electrolyte for Flexible SEI Formation
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Solution Overview
Problem
Current silicon-containing anode materials in lithium ion batteries suffer from significant drawbacks, including large volume changes that lead to physical damage, loss of electrical contact, and irreversible capacity fading due to the formation of a solid electrolyte interface (SEI) layer, limiting their cycle life and charge capacity.
Innovation Solution
An electrolyte system that promotes the passive formation of a flexible protective solid electrolyte interface (SEI) layer comprising a lithium fluoride (LiF)-polymer composite on the surface of silicon-containing electroactive materials, using a combination of cyclic and linear carbonate co-solvents, including fluoroethylene carbonate and 2,2-difluoroethyl methyl carbonate, to accommodate volumetric expansion and contraction, thereby enhancing long-term cycling stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-containing anode materials are used to increase charge capacity, then the theoretical charge capacity is improved, but large volume changes occur during lithium alloying/dealloying causing physical damage and loss of electrical contact
Solution Approach 1:
The patent applies this principle by forming a flexible protective SEI layer on the silicon-containing electroactive material surface. This flexible film accommodates the large volumetric expansion and contraction of silicon during lithium alloying and dealloying cycles, preventing physical damage such as cracking and flaking while maintaining structural integrity and electrical contact.
Solution Approach 2:
The patent applies this principle by pre-forming a protective solid electrolyte interface (SEI) layer on the silicon surface before it undergoes volume changes. This pre-formed protective layer acts as a cushion that absorbs and accommodates the mechanical stress from volumetric expansion and contraction, preventing direct damage to the silicon substrate during cycling.
2Reliability
If conventional electrolyte systems are used with silicon anodes, then a solid electrolyte interface (SEI) layer forms on the active material surface, but this causes continuous electrolyte consumption and lithium ion loss leading to irreversible capacity fading
Solution Approach 1:
The patent applies this principle by changing the chemical composition parameters of the electrolyte system. Specifically, it uses a carbonate-based electrolyte containing fluoroethylene carbonate (FEC) at 5-50 vol% and 2,2-difluoroethyl methyl carbonate (2F-EMC) at 5-80 vol%, which alters the SEI formation chemistry to produce a more stable and protective layer that reduces continuous electrolyte consumption and lithium ion loss.
Solution Approach 2:
The patent applies this principle by creating a composite SEI layer with specific chemical composition. The electrolyte system produces an SEI layer that is enriched in lithium fluoride (LiF) and contains polymer components, forming a composite protective layer that is more stable and less consumptive than conventional SEI layers.
3Reliability
If the SEI layer is formed to protect the silicon surface, then protection is provided, but the layer must be flexible to accommodate volumetric expansion and contraction during cycling
Solution Approach 1:
The patent applies this principle by forming a flexible protective SEI layer on the silicon-containing electroactive material surface. This flexible film accommodates the large volumetric expansion and contraction of silicon during lithium alloying and dealloying cycles, preventing physical damage such as cracking and flaking while maintaining structural integrity and electrical contact.
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 flexible SEI layer minimizes electrolyte consumption and lithium ion loss, improving the cycle life and charge capacity of silicon-containing electrodes, maintaining performance even at low temperatures and reducing capacity fade.
Implementation Method 1
a solid electrolyte interface (SEI) layer formation can form on the active material surface
Implementation Method 2
Contact of the anode and cathode materials with the electrolyte can create an electrical potential between the electrodes. When electron current is generated in an external circuit between the electrodes, the potential is sustained by electrochemical reactions within the cells of the battery.
Implementation Method 3
The large volume changes (e.g., volume expansion/contraction) of silicon-containing materials during lithium alloy/dealloy, insertion/extraction (e.g., intercalation and deintercalation)
Implementation Method 4
The electrolyte is suitable for conducting lithium ions and may be in solid or liquid form. Lithium ions move from a cathode (e.g., positive electrode) to an anode (e.g., negative electrode) during charging of the battery, and in the opposite direction when discharging the battery.
Data Source
AI summary
Electrochemical cells that cycle lithium ions are provided. The electrochemical cells have an electrode that includes a silicon-containing electroactive material that undergoes volumetric expansion and contraction during the cycling of the electrochemical cell; and an electrolyte system that promotes passive formation of a flexible protective layer comprising a lithium fluoride-polymer composite on one or more exposed surface regions of the silicon-containing electroactive material. The electrolyte system includes a lithium salt, at least one cyclic carbonate, and two or more linear carbonates. At least one of the two or more linear carbonate-containing co-solvents is a fluorinated carbonate-containing co-solvent. The electrolyte system accommodates the volumetric expansion and contraction of the silicon-containing electroactive material to promote long term cycling stability.