Branched-Ester Electrolyte for Lithium Battery SEI Stability
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Solution Overview
Problem
Lithium secondary batteries face issues with the stability of the solid electrolyte interface (SEI) layer at high temperatures, leading to increased inner pressure and poor conductivity at low temperatures, which affects their life cycle and performance.
Innovation Solution
A non-aqueous electrolyte solution for lithium secondary batteries is developed, comprising an electrolyte salt and an organic solvent with a cyclic carbonate or linear carbonate, ether, ester, or amide, where the solvent includes an ester-based compound with a branched-chain alkyl group, such as isobutyl propionate, in a range of 50 to 90 vol%, to enhance stability and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ethylene carbonate is used as a solvent to provide high operation voltage and stable SEI layer, then the battery can operate at high voltage (3.6-3.7V), but the SEI layer becomes unstable at high temperatures causing continuous gas generation and battery swelling
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by introducing esters with branched-chain alkyl groups (isobutyl propionate, isoamyl propionate, isobutyl butylate, ethyl 2-methyl butylate, methyl 2-methyl butyrate, methyl isovalerate, propyl-2-methyl butylate, or propyl isovalerate) in specific proportions (5-50 mass%). This compositional parameter change modifies the SEI layer formation characteristics, making it more stable at high temperatures while maintaining the electrochemical stability needed for high voltage operation.
Solution Approach 2:
The patent creates a composite electrolyte system by combining ethylene carbonate (cyclic carbonate) with specific esters having branched-chain alkyl groups. This composite approach leverages the high voltage stability of ethylene carbonate while the ester components contribute to forming a more thermally stable SEI layer, reducing gas generation and improving high-temperature performance without sacrificing the electrochemical window.
2Reliability
If ethylene carbonate is used to form SEI layer, then it prevents organic solvent insertion and protects anode structure, but it has high freezing point (37-39°C) and low ionic conductivity at low temperatures
Solution Approach 1:
The patent modifies the electrolyte composition by adding esters with branched-chain alkyl groups in optimized proportions (5-50 mass%). These esters lower the freezing point of the electrolyte mixture and enhance ionic conductivity at low temperatures while the ethylene carbonate component continues to provide effective SEI layer formation for anode protection. The synergistic combination resolves the contradiction between anode protection and low-temperature conductivity.
3Productivity
If carbonate-based organic solvent is used to enable lithium ion transfer, then it allows stable charging/discharging through SEI layer formation, but it decomposes to generate gas (CO, CO2, CH4, C2H6) causing battery swelling
Solution Approach 1:
The patent converts the harmful gas-generating decomposition reaction of carbonate solvents into a beneficial process by introducing esters with branched-chain alkyl groups. These esters preferentially react during initial cycles to form a stable SEI layer that is less prone to continuous decomposition. The modified SEI layer allows lithium ion transport while significantly reducing ongoing gas generation from carbonate solvent decomposition, thus converting the harmful continuous decomposition into a controlled initial formation process.
Solution Approach 2:
By changing the electrolyte composition to include specific esters (5-50 mass%), the patent alters the decomposition behavior of the carbonate solvent. The ester components modify the chemical environment at the electrode interface, suppressing the continuous decomposition of carbonate solvents that leads to gas generation, while maintaining the essential ion transfer functionality.
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 life characteristics and stability of lithium secondary batteries at both room and high temperatures, minimizing capacity decrease and thickness change, even after repeated charging/discharging cycles.
Implementation Method 1
high reactive lithium reacts with the electrolyte solution and carbon present in the anode active material such as graphite to produce a compound such as Li2CO3, Li2O and LiOH. The produced compound forms a kind of a solid electrolyte interface (SEI) layer on the surface of the anode active material such as graphite.
Implementation Method 2
The SEI layer functions as an ion tunnel, allowing only lithium ions to pass through.
Implementation Method 3
a non-aqueous electrolyte solution obtained by dissolving a suitable amount of lithium salt in a mixed organic solvent... acts as a source for supplying lithium ions in a battery
Data Source
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AI summary
The present invention provides a non-aqueous electrolyte solution for a lithium secondary battery, comprising an ester-based compound having a branched-chain alkyl group; and a lithium secondary battery using the same.