Lithium Ion Cell Electrolyte Moisture Control
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Solution Overview
Problem
Lithium ion secondary cells using fluorine-containing lithium salts face increased internal resistance due to the formation of hydrogen fluoride, which degrades charging and discharging cycle characteristics, and the use of additives to prevent this can inadvertently increase resistance.
Innovation Solution
Incorporating a compound represented by chemical formula (I) as an additive in the non-aqueous electrolyte, with a specific mole ratio to consume moisture and prevent HF formation, while avoiding excessive additive amounts that could increase resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a salt containing an anion having a dicarboxylic acid group is added to the electrolyte to consume moisture and suppress HF formation, then the formation of HF is suppressed, but the internal resistance increases due to decomposed products deposited on the electrode surfaces
Solution Approach 1:
The patent changes the chemical structure parameters of the additive by specifying exact molecular formulas (C10H10O6 for compound I and C12H14O8 for compound II) and their molar ratios relative to moisture content. This precise parameter control allows the additive to consume moisture effectively while minimizing resistance-increasing decomposed products on electrode surfaces.
Solution Approach 2:
The patent uses a composite approach by combining two specific compounds (I and II) with fluorine-containing lithium salts in defined proportions. This composite electrolyte formulation achieves synergistic effects where the combination of compounds suppresses HF formation more effectively while controlling the deposition of decomposed products better than either compound alone.
2Quantity of substance
If fluorine-containing lithium salts are used as supporting salts to achieve high energy density, then the energy density is high, but internal resistance increases due to hydrolysis reaction with water forming HF
Solution Approach 1:
The patent introduces compounds I and II as intermediary substances that mediate between the fluorine-containing lithium salts and moisture. These compounds preferentially react with trace water to form stable products, preventing the hydrolysis of fluorine-containing lithium salts and thus suppressing HF formation while maintaining the high energy density benefits of the fluorine-containing salts.
Solution Approach 2:
The patent applies preliminary anti-action by adding compounds I and II before any hydrolysis can occur. These compounds preemptively consume any trace moisture present in the electrolyte system, creating a protective effect that prevents subsequent HF formation and collector corrosion, thereby maintaining low internal resistance throughout the cell's operational life.
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
This approach effectively suppresses the formation of hydrogen fluoride, reducing initial and endurance resistance, thereby improving the charging and discharging cycle characteristics of lithium ion secondary cells.
Implementation Method 1
when the lithium salt including fluorine as a constituent element as described above reacts with water, the lithium salt may be decomposed to form hydrogen fluoride (HF)
Data Source
AI summary
There is provided a lithium ion secondary cell excellent in charging and discharging cycle characteristics. A lithium ion secondary cell includes: an electrode body including a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a separator; and a non-aqueous electrolyte containing a lithium salt as a supporting salt in an organic solvent, the electrode body and the non-aqueous electrolyte being accommodated in a case. The positive electrode active material is a lithium transition metal oxide having a layered structure. The electrolyte contains a compound represented by a chemical formula (I) in an amount of β mol relative to the total content α mol of moisture to be mixed in the cell. β satisfies −1.3≦log(β/α)≦1.