Fluorinated Electrolyte Composition for Stable Lithium Metal Cycling
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Solution Overview
Problem
Lithium-ion electrochemical elements with a lithium metal anode face challenges in cyclability due to dendrite growth, leading to short circuits and irreversible failure, and existing solutions either fail to address dendrite issues or increase internal resistance, limiting their high-temperature performance and capacity retention.
Innovation Solution
An electrochemical element with a lithium anode or lithium alloy, using a solvent mixture of 1,1,1,3,3-hexafluoro-2-methoxypropane and ethylene monofluorocarbonate, along with lithium difluorophosphate as an additive, which enhances cyclability and reduces the risk of dendrite formation, allowing operation up to 85°C with minimal capacity loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a lithium metal anode is used to increase capacity, then the capacity increases significantly (about 3860 mAh/g vs 370 mAh/g for graphite), but lithium dendrites form during cycling leading to short circuits and cell failure
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by introducing fluorinated carbonates (F3EMC, F3EA) and fluorinated ethers (HFMP, HFMFP) with specific fluorine-containing functional groups. These compositional changes modify the electrolyte's properties to enable stable lithium deposition without dendrite formation, resolving the contradiction between high capacity and cyclability
Solution Approach 2:
The patent uses a composite electrolyte system combining multiple fluorinated components (fluorinated carbonates and fluorinated ethers) with lithium salts. This composite approach creates synergistic effects where the fluorinated molecules work together to form a stable SEI layer that prevents dendrite growth while maintaining high lithium capacity
2Reliability
If a thick separator is used to prevent dendrite penetration, then short circuit risk is reduced, but internal resistance increases and power performance decreases
Solution Approach 1:
The fluorinated electrolyte components act as intermediary substances that mediate between the lithium anode and the separator. The fluorinated molecules (F3EMC, F3EA, HFMP, HFMFP) form a protective interface layer that prevents dendrite penetration through thin separators, eliminating the need for thick separators and thus maintaining power performance while ensuring dendrite resistance
3Ease of manufacture
If conventional electrolyte compositions are used with lithium metal anodes, then manufacturing is simpler, but the cells cannot operate reliably at high temperatures (above 25°C) with good capacity retention
Solution Approach 1:
The patent modifies the electrolyte's thermal stability parameters by incorporating fluorinated carbonates and ethers. The fluorine atoms in these molecules enhance the electrolyte's thermal resistance, allowing the cell to operate at high temperatures (up to 85°C) without degradation, while maintaining manufacturing simplicity through direct electrolyte formulation changes
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 solution significantly improves the lifespan and safety of lithium-ion elements by preventing dendrite growth and maintaining capacity at high temperatures, while also reducing the risk of ignition and internal pressure issues.
Implementation Method 1
lithium difluorophosphate LiPO2F2, which forms a stable solid electrolyte interface (SEI) layer on the lithium anode surface during initial charging cycles. This SEI layer acts as a protective barrier that prevents direct contact between the electrolyte and lithium metal, thereby suppressing dendrite formation and improving cyclability
Implementation Method 2
a liquid or gelled electrolyte composition comprising: a) a solvent comprising: i) either a mixture of 1,1,1,3,3,3-hexafluoro-2-methoxypropane (HFMP) and/or 1,1,1,3,3,3-hexafluoro-2-(fluoromethoxy)propane (HFMFP), ethylene monofluorocarbonate (F1EC) and 2,2,2-trifluoroethyl methyl carbonate (F3EMC)
Data Source
Figure 1~2a
Figure 2b~3
Figure 4~5a
AI summary
The invention relates to an electrochemical cell comprising: - at least one anode comprising metallic lithium or a lithium alloy or at least one anode comprising a current collector at least partially covered with metallic lithium deposited after at least one charge of the cell, the cell not containing metallic lithium at the time of its manufacture, - at least one cathode, - a liquid or gelled electrolyte composition comprising: a) a solvent comprising: i) either a mixture of 1,1,1,3,3,3-hexafluoro-2-methoxypropane (HFMP) and/or 1,1,1,3,3,3-hexafluoro-2-(fluoromethoxy)propane (HFMFP), ethylene monofluorocarbonate (F1EC) and 2,2,2-trifluoroethyl methyl carbonate (F3EMC), ii) or a mixture of 1,1,1,3,3,3-hexafluoro-2-methoxypropane (HFMP) and/or 1,1,1,3,3,3-hexafluoro-2-(fluoromethoxy)propane (HFMFP), ethylene monofluorocarbonate (F1EC) and 2,2,2-trifluoroethyl acetate (F3EA), b) at least one salt whose cation is the lithium cation, c) lithium difluorophosphate LiPO2F2 in an amount representing from 0.05 to 5% of the mass of the combination made up of the solvent and said at least one dissolved lithium salt.