Lithium Ion Cell Electrolyte Additive for Cycle Life
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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, which consumes moisture to suppress HF formation, and calculating its amount based on a specific mathematical expression to balance moisture consumption and prevent excessive additive effects, thereby maintaining low internal 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 and collector corrosion is reduced, 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 particular substituents (R1-R6) in the dicarboxylic acid salt formula, and optimizes the amount parameter by defining a specific ratio range (0.01-5% by mass relative to lithium salt). This resolves the contradiction by finding the optimal balance between moisture consumption capability and resistance increase caused by decomposition products.
Solution Approach 2:
The patent creates a composite electrolyte system combining the lithium salt, non-aqueous solvent, and dicarboxylic acid salt additive in specific proportions. This composite approach allows the additive to perform its moisture-consuming function while the overall composition is optimized to minimize the harmful effects of decomposition products on internal resistance.
2Object-affected harmful factors
If the amount of additive is increased to enhance moisture consumption, then HF formation is further suppressed, but the increase in internal resistance becomes more significant
Solution Approach 1:
The patent defines a specific parameter range for the additive amount (0.01-5% by mass relative to lithium salt) to optimize the balance between moisture consumption and resistance control. This quantitative parameter optimization resolves the contradiction by identifying the optimal dosage that provides sufficient HF suppression while minimizing resistance increase from decomposition products.
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 effectively suppresses the formation of hydrogen fluoride, reducing initial and endurance resistance, and improving the charging and discharging cycle characteristics of lithium ion secondary cells.
Implementation Method 1
a salt containing an anion having a dicarboxylic acid group is added as an additive; as a result, the moisture in the cell is consumed
Implementation Method 2
The lithium ions in the electrolyte come and go between both the electrodes for performing charging and discharging
Implementation Method 3
at least a part of the additive is decomposed by a charging treatment, and that the decomposed products are deposited on the surfaces of the positive electrode and/or the negative electrode
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 spinel type 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 −0.8≦log(β/α)≦1.5.