Complex Battery Electrolytes for Stable SEI on High-Capacity Anodes
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Solution Overview
Problem
Conventional metal-ion batteries face challenges such as large irreversible capacity losses, low Coulombic Efficiency, and poor stability of the solid electrolyte interphase (SEI) due to volume changes and undesirable reactions with electrolytes, limiting their application in high-power devices.
Innovation Solution
The development of complex electrolyte compositions that include a mixture of Li-ion salts with other metal salts having a standard reduction potential below −2.3 V vs. Standard Hydrogen Electrode (SHE), along with the use of ether solvents and specific salt concentrations, aims to enhance SEI stability, reduce solvent diffusion, and improve electrode performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If alloying-type anodes (such as silicon) are used to achieve higher specific capacity, then the energy density is improved, but the volume changes during cycling cause poor SEI stability and large irreversible capacity losses
Solution Approach 1:
The patent modifies the chemical composition parameters of the electrolyte by incorporating specific additives (fluoroethylene carbonate, vinylene carbonate, and lithium fluoride) to change the properties of the SEI layer. This allows the SEI to remain stable despite the volume changes in alloying anodes, resolving the contradiction between high capacity and reliability.
Solution Approach 2:
The patent introduces intermediary substances (electrolyte additives and lithium fluoride) that mediate between the alloying anode and the bulk electrolyte. These intermediaries form a protective SEI layer that accommodates volume changes while preventing harmful reactions, thus maintaining stability during high-capacity cycling.
2Productivity
If conventional electrolytes are used with high capacity anodes, then the cell operates normally, but the SEI grows rapidly leading to degradation of cell performance
Solution Approach 1:
The patent converts the harmful effect of electrolyte decomposition into a beneficial outcome by controlling the decomposition process through specific additives. The additives guide the decomposition to form a stable, protective SEI layer rather than allowing uncontrolled growth that causes capacity loss, thus turning the harmful decomposition into a beneficial protective mechanism.
3Power
If higher voltage cathodes are used to increase energy density, then the power output is improved, but oxidation of conventional electrolytes occurs leading to gassing and rapid cell degradation
Solution Approach 1:
The patent changes the chemical parameters of the electrolyte composition to increase its oxidation resistance. By incorporating specific additives and adjusting the composition ratios, the electrolyte can withstand higher voltages without oxidizing, enabling high-power cathodes to operate without causing gassing or degradation.
4Reliability
If carbon-based anodes are used to ensure stability, then the Coulombic Efficiency is maintained, but the specific capacity is limited compared to alloying materials
Solution Approach 1:
The patent employs composite anode structures combining carbon-based materials with alloying materials. The carbon component provides stability and maintains Coulombic Efficiency, while the alloying component contributes high specific capacity. The optimized electrolyte composition ensures both materials work synergistically without compromising overall cell performance.
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 complex electrolyte compositions effectively combat SEI growth on high capacity anodes, reduce undesirable reactions with high capacity cathodes, and enhance the stability and performance of metal-ion batteries, enabling the fabrication of high voltage and high capacity batteries at a lower cost than conventional Li-ion battery technology.
Implementation Method 1
The SEI growth is primarily caused by permeation of the electrolyte solvent through the existing SEI to the active material surface at low potentials
Implementation Method 2
The SEI comprises products of the electrolyte decomposition on the electrode during cell operation
Data Source
AI summary
Batteries such as Li-ion batteries are provided that comprise anode and cathode electrodes, an electrolyte ionically coupling the anode and the cathode, and a separator electrically separating the anode and the cathode. In some designs, the electrolyte may comprise, for example, a mixture of (i) a Li-ion salt with (ii) at least one other metal salt having a metal with a standard reduction potential below −2.3 V vs. Standard Hydrogen Electrode (SHE). In other designs, the electrolyte may be disposed in conjunction with an electrolyte solvent that comprises, for example, about 10 to about 100 wt. % ether. In still other designs, the battery may further comprise anode and cathode interfacial layers (e.g., solid electrolyte interphase (SEI)) disposed between the respective electrode and the electrolyte and having different types of fragments of electrolyte solvent molecules as compared to each other.