Halogen-Substituted Cyclic Carbonate and Vinyl Compound Electrolyte for SEI Stability
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Solution Overview
Problem
Lithium secondary batteries with non-aqueous electrolytes face issues with lithium ion conductivity and stability due to the breakdown of the solid electrolyte interface (SEI) layer, particularly at high temperatures, which degrades battery performance and increases internal pressure.
Innovation Solution
Incorporating a halogen-substituted cyclic carbonate compound and a vinyl group containing compound in the electrolyte to form a synergistic SEI layer that enhances stability and lithium ion conductivity, optimizing the SEI layer's properties through a combination of compounds that individually address stability and conductivity inconsistencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a non-aqueous electrolyte is used in lithium secondary batteries, then energy density and drive voltage are improved, but lithium ion conductivity is reduced compared to aqueous electrolyte batteries
Solution Approach 1:
The patent modifies the chemical composition parameters of the electrolyte by introducing specific additives (vinylene carbonate at 0.01-5 wt% and fluoroethylene carbonate at 0.01-5 wt%) to change the properties of the SEI layer, thereby improving lithium ion conductivity while maintaining the high energy density benefits of non-aqueous electrolytes
Solution Approach 2:
The patent uses vinylene carbonate and fluoroethylene carbonate as intermediary substances that mediate between the electrode and the bulk electrolyte, forming an optimized SEI layer that enables efficient lithium ion transport while maintaining the advantages of non-aqueous electrolyte systems
2Reliability
If vinylene carbonate is used as an electrolyte additive to form an SEI layer, then the SEI layer is formed on the anode surface, but the SEI layer has high resistance and is subject to break-down at high temperatures
Solution Approach 1:
The patent combines vinylene carbonate and fluoroethylene carbonate in a specific ratio (0.01:0.01 to 5:5 wt%) to create a synergistic effect where the resulting SEI layer inherits the film-forming capability of VC and the thermal stability of FEC, resolving the high temperature break-down issue
Solution Approach 2:
The patent creates a composite SEI layer structure through the combined action of two different electrolyte additives, where the composite structure provides both the low resistance characteristics from VC and the high temperature stability from FEC that neither component could achieve alone
3Reliability
If the SEI layer is formed by reduction of electrolyte solvent during initial charge, then the anode surface is protected, but the SEI layer is insufficient to continuously protect the anode during charge/discharge cycles
Solution Approach 1:
The patent uses electrolyte additives that act during the initial charge cycles to pre-form an optimized SEI layer with superior properties, which then provides continuous protection throughout subsequent charge/discharge cycles, extending the duration of effective anode protection
Solution Approach 2:
The patent changes the compositional parameters of the SEI layer by introducing specific electrolyte additives, transforming it from a simple reduction product into a stable, protective interface that maintains its integrity over extended charge/discharge cycling
4Power
If a battery is driven at high temperatures, then power delivery is improved, but the SEI layer breaks down due to thermal instability, causing gas generation and increased internal pressure
Solution Approach 1:
The patent converts the potential harm of high temperature operation into a benefit by using electrolyte additives that form an SEI layer specifically designed to be thermally stable, allowing the battery to safely deliver high power at elevated temperatures without the harmful gas generation that would normally occur
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 combined use of these compounds improves the battery's lifetime characteristic and high-temperature performance by maintaining physical and structural stability of the SEI layer, reducing irreversible lithium consumption, and minimizing capacity drop, while maintaining high lithium ion conductivity.
Implementation Method 1
a solid electrolyte interface (hereinafter, referred to as SEI) layer formed on an anode surface by reduction of an electrolyte solvent during an initial charge of a battery
Implementation Method 2
the SEI layer formed on an anode surface by reduction of an electrolyte solvent during an initial charge of a battery
Data Source
AI summary
Disclosed is a secondary battery including an electrolyte and/or an electrode, the electrolyte including an electrolyte salt and an electrolyte solvent, i) a cyclic carbonate compound substituted with at least one halogen element; and ii) a compound containing a vinyl group in a molecule thereof, and the electrode including a solid electrolyte interface (SEI) layer partially or totally formed on the surface thereof by electrical reduction of the two compounds.