Lithium-Ion Battery Electrolyte for High-Temperature Separator Wetting
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Solution Overview
Problem
Existing lithium ion secondary batteries face challenges in achieving both high-temperature safety and battery characteristics due to issues with impregnability of polyolefin separators and viscosity, particularly when using cyclic and chain carbonates, which affect flash points and ionic conductivity.
Innovation Solution
A nonaqueous electrolytic solution comprising 80-100% ethylene carbonate, propylene carbonate, and γ-butyrolactone with trifluoroacetic acid esters and pivalic acid esters having a carbon chain length of 6 to 8, along with specific electrolyte salts and additives, to enhance impregnability and reduce viscosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cyclic carbonate (EC, PC, GBL) is used to enhance thermal stability and flash point, then battery safety at high temperature is improved, but impregnability of polyolefin separator deteriorates
Solution Approach 1:
The patent combines cyclic carbonate (providing high flash point and thermal stability) with chain carbonate (providing good impregnability of separator) in a specific ratio. This merging allows the electrolytic solution to simultaneously achieve both high-temperature safety and effective separator impregnation, resolving the contradiction between these two opposing requirements.
Solution Approach 2:
The electrolytic solution uses a composite solvent system comprising both cyclic carbonate and chain carbonate components. This composite approach leverages the advantageous properties of each component type: the cyclic carbonate provides thermal stability while the chain carbonate ensures separator penetration, creating a synergistic effect that resolves the technical contradiction.
2Ease of operation
If chain carbonate (DMC, EMC, DEC) is used to improve impregnability of polyolefin separator, then separator penetration is improved, but flash point is lowered to about 25°C
Solution Approach 1:
The patent merges chain carbonate (which provides excellent separator impregnability) with cyclic carbonate (which provides high flash point). By combining these two types of carbonates in a specific proportion, the resulting electrolytic solution achieves both good separator penetration and high thermal stability, eliminating the need to choose between these conflicting properties.
Solution Approach 2:
The patent changes the compositional parameters of the electrolytic solution by controlling the ratio of cyclic carbonate to chain carbonate. By adjusting these parameters within specific ranges, the solution optimizes both the flash point and impregnability properties simultaneously, resolving the contradiction through parameter optimization.
3Productivity
If pivalic acid ester with long carbon chain (e.g., octyl pivalate) is used to enhance separator impregnability, then manufacturing time is reduced, but viscosity increases above GBL
Solution Approach 1:
The patent optimizes the carbon chain length parameter of the pivalic acid ester within a specific range (6-10 carbon atoms). By controlling this parameter, the solution achieves effective separator impregnation and reduced manufacturing time while keeping viscosity within acceptable limits, avoiding the excessive viscosity associated with longer chains like octyl pivalate.
Solution Approach 2:
The patent applies the concept of local quality by selecting pivalic acid esters with specific carbon chain lengths that provide adequate impregnability for the separator without causing excessive viscosity throughout the entire electrolytic solution. This localized optimization of molecular structure achieves the desired balance between manufacturing efficiency and fluidity.
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 improved battery safety at high temperatures with enhanced impregnability and cycle properties, allowing for efficient manufacturing and maintaining battery performance.
Implementation Method 1
a microporous separator quickly penetrates into a porous structure of the separator
Implementation Method 2
an electrolyte salt dissolved in a nonaqueous solvent
Data Source
Figure 1
AI summary
An object of the present disclosure is to provide a nonaqueous electrolytic solution and a lithium ion secondary battery using same, the nonaqueous electrolytic solution having both excellent battery safety when used at a high temperature, an important feature for secondary batteries to be installed in modern vehicles such as electric vehicles, and having excellent battery characteristics. The nonaqueous electrolytic solution of the present disclosure is a nonaqueous electrolytic solution including an electrolyte salt dissolved in a nonaqueous solvent, the nonaqueous solvent containing from 80 to 100 vol% in total of at least one selected from ethylene carbonate, propylene carbonate, and γ-butyrolactone, and the nonaqueous electrolytic solution further including a trifluoroacetic acid ester having an alcohol group with a carbon chain length of from 6 to 8.