Liquid Electrolyte Composition for High-Voltage Lithium Cell Stability
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Solution Overview
Problem
Current lithium-ion batteries face limitations in energy density and safety due to electrolyte stability issues, particularly at higher operating voltages, leading to poor cyclability and flammability, which restricts their application in high-end portable devices.
Innovation Solution
An electrolyte composition comprising lithium bis(trifluoromethansolfonyl)imide (LiTFSI), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), sulfolane (SL), and fluoroethylene carbonate (FEC) is used, with specific molar ratios and volume percentages to enhance stability and safety, allowing for higher energy density and extended cycle life at voltages above 4.4V.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional electrolyte solvents (EC, DMC, PC) are used, then ionic conductivity is achieved, but electrolyte stability deteriorates at high operating voltages leading to decomposition and flammability
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by replacing conventional carbonate solvents with fluorinated solvents (TTE, BTFE, TFTFE) and using fluorinated lithium salts (LiTFSI, LiBF4, LiPF6). This parameter change fundamentally alters the electrolyte's stability characteristics, enabling operation at high voltages (4.4V-4.5V) while maintaining safety by reducing flammability and preventing decomposition.
Solution Approach 2:
The patent employs a composite electrolyte system combining multiple fluorinated components: fluorinated solvents (TTE, BTFE, TFTFE), fluorinated lithium salts (LiTFSI, LiBF4, LiPF6), and cyclic carbonate additives (FEC, GM). This composite approach creates synergistic effects where each component contributes to overall stability, ionic conductivity, and safety, resolving the contradiction between achieving necessary ionic transport and preventing harmful decomposition.
2Productivity
If operating voltage is increased to 4.4V or higher for high energy density, then battery capacity improves, but electrolyte stability deteriorates causing poor cyclability
Solution Approach 1:
The patent changes the electrochemical stability window parameters by introducing fluorinated solvents and salts that maintain stability at potentials above 4.4V. Specifically, TTE, BTFE, and TFTFE provide a wider electrochemical stability window compared to conventional carbonates, enabling high-voltage operation (4.4V-4.5V) while maintaining excellent cyclability over extended periods.
Solution Approach 2:
The patent uses cyclic carbonate additives (FEC, GM) as intermediary substances that form protective interfacial films on the electrodes. These intermediary layers mediate between the high-voltage operating conditions and the electrode materials, preventing direct harmful interactions while allowing ionic transport, thus preserving cycle life at elevated voltages.
3Productivity
If lithium metal anode is used to increase energy density, then battery capacity improves, but coulombic efficiency deteriorates leading to poor cyclability
Solution Approach 1:
The patent employs fluorinated lithium salts (LiTFSI, LiBF4, LiPF6) and cyclic carbonate additives (FEC, GM) as intermediary substances that mediate between the lithium metal anode and the electrolyte. These intermediaries form stable solid electrolyte interface (SEI) layers that enable efficient lithium ion transport while preventing electrolyte decomposition, achieving high coulombic efficiency (≥93%) with lithium metal anodes.
Solution Approach 2:
The patent changes the interfacial properties parameters by using fluorinated components that modify the SEI formation characteristics. The fluorinated lithium salts and cyclic carbonates alter the composition and structure of the SEI layer, optimizing it for lithium metal anodes to achieve high coulombic efficiency and stable cycling performance.
4Ease of manufacture
If conventional electrolyte composition is used, then manufacturing simplicity is maintained, but safety deteriorates due to flammability
Solution Approach 1:
The patent changes the fundamental chemical parameters of the electrolyte by substituting conventional hydrocarbon-based carbonates with fluorinated solvents (TTE, BTFE, TFTFE) and fluorinated lithium salts. This parameter change inherently reduces flammability while maintaining ease of manufacture, as the fluorinated components can be directly mixed in specified ratios without complex processing steps.
Solution Approach 2:
The patent creates a composite fluorinated electrolyte system combining fluorinated solvents, fluorinated lithium salts, and cyclic carbonate additives. This composite formulation achieves safety by reducing flammability through fluorinated components while maintaining manufacturing simplicity through a straightforward mixing process with defined composition ranges.
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 composition achieves a coulombic efficiency of at least 93%, significantly improving energy density and cycle life while ensuring safety, enabling lithium-ion batteries to operate effectively at higher voltages with reduced flammability risks.
Implementation Method 1
The electrolyte should conduct lithium ions, acting as a carrier between the cathode and the anode when a battery passes an electric current through an external circuit
Implementation Method 2
Electrolyte solvents in current use decompose on initial charging and form a solid interphase layer, which is electrically insulating, yet provides sufficient ionic conductivity
Data Source
AI summary
The present invention relates to an electrochemical cell comprising a positive electrode, a negative electrode and a liquid electrolyte comprising a specific lithium salt, preferably lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), a fluorinated ether, preferably 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), a cyclic sulfone, preferably sulfolane (SL), and a fluorinated carbonate, preferably fluoroethylene carbonate (FEC), in an amount (x) of 0<x<=15 vol. %, wherein the electrochemical cell has a Coulombic efficiency of at least 93%. The electrolyte used according to the invention results in improved electrochemical properties.