Non-aqueous Electrolyte Solvent Mixture for Lithium Cell Safety
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Solution Overview
Problem
Current non-aqueous electrolytic solutions for lithium secondary cells face challenges in achieving good solubility of electrolyte salts while ensuring flame retardancy and maintaining cell characteristics such as charge and discharge cycle characteristics and discharge capacity, especially at low temperatures.
Innovation Solution
A non-aqueous electrolytic solution comprising a solvent mixture of fluorine-containing ethers or carbonates, non-fluorine-containing cyclic carbonates, and chain esters, optimized in specific volume ratios to enhance solubility, flame retardancy, and cell performance, including the use of electrolyte salts like LiPF6 and LiN(SO2CF3)2, which improves discharge capacity, rate characteristics, and low-temperature stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If fluorine-containing solvents are added to enhance flame retardancy, then incombustibility is improved, but solubility of electrolyte salt decreases and viscosity increases
Solution Approach 1:
The patent uses a composite solvent system combining fluorine-containing cyclic carbonate (for flame retardancy), non-fluorine-containing cyclic carbonate (for electrolyte salt solubility), and chain carbonate (for low viscosity). This composite approach allows each component to contribute its strengths: the fluorine-containing compound provides safety, the non-fluorine cyclic carbonate ensures good solubility of LiPF6 and LiBF4, and the chain carbonate maintains low viscosity for good rate characteristics.
2Object-affected harmful factors
If fluorine-containing solvents are added to enhance flame retardancy, then incombustibility is improved, but viscosity increases and rate characteristic decreases
Solution Approach 1:
The patent employs a composite solvent system where fluorine-containing cyclic carbonate (providing flame retardancy) is combined with chain carbonate (providing low viscosity). The chain carbonate component specifically addresses the viscosity issue by maintaining fluidity and ion mobility, thereby preserving good rate characteristics while the fluorine-containing compound ensures safety.
3Quantity of substance
If chain carbonate is used to improve solubility and low viscosity, then electrolyte salt solubility and rate characteristic are improved, but flame retardancy decreases
Solution Approach 1:
The patent creates a balanced composite solvent system where chain carbonate (providing good solubility and low viscosity) is combined with fluorine-containing cyclic carbonate (providing flame retardancy). The non-fluorine-containing cyclic carbonate further enhances electrolyte salt solubility. This combination allows the system to achieve good solubility, low viscosity, and flame retardancy simultaneously.
4Quantity of substance
If non-aqueous electrolytic solution is designed for high energy density, then cell capacity is improved, but safety and incombustibility deteriorate
Solution Approach 1:
The patent develops a composite solvent system that maintains high cell capacity while ensuring safety through flame retardancy. The fluorine-containing cyclic carbonate provides the necessary flame retardant properties, while the non-fluorine-containing cyclic carbonate and chain carbonate ensure good electrolyte salt solubility and ion conductivity, thereby maintaining high cell capacity and 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
The solution provides a non-aqueous electrolytic solution with high solubility of electrolyte salts, improved cell capacity, and excellent rate and cycle characteristics, maintaining stability even at low temperatures, and is suitable for lithium secondary cells, enhancing safety and performance.
Implementation Method 1
a solvent (I) for dissolving an electrolyte salt comprising... (A1) ethers of the formula Rf1ORf2... (A2) carbonates of the formula Rf4OCOORf5
Implementation Method 2
addition of a non-fluorine-containing chain ester or a fluorine-containing chain ester as a low viscosity solvent to the electrolytic solution enhances cell capacity and rate characteristic
Implementation Method 3
addition of a fluorine-containing solvent is proposed... enhancement of incombustibility of a non-aqueous electrolytic solution
Data Source
AI summary
There is provided a non-aqueous electrolytic solution assuring good solubility of an electrolyte salt and having enough cell characteristics (charge and discharge cycle characteristic, discharge capacity, and the like), and the non-aqueous electrolytic solution comprises a solvent for dissolving an electrolyte salt comprising (A) at least one fluorine-containing solvent selected from the group consisting of fluorine-containing ethers and fluorine-containing carbonates, (B) a non-fluorine-containing cyclic carbonate and (C) a chain ester represented by the formula (C): R1COOR2, wherein R1 is an alkyl group having 2 to 4 carbon atoms; R2 is an alkyl group having 1 to 4 carbon atoms or a fluorine-containing alkyl group having 1 to 4 carbon atoms, and (II) an electrolyte salt.