Lithium Secondary Cell Electrolyte Safety and Performance
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Solution Overview
Problem
Lithium secondary cells using fluorine-containing non-aqueous electrolytic solutions face limitations in discharge capacity, rate characteristics, and cycle characteristics, while also requiring improved safety features such as incombustibility.
Innovation Solution
A lithium secondary cell design incorporating a negative electrode with lithium titanate and a non-aqueous electrolytic solution comprising a fluorine-containing solvent, specifically a mixture of fluorine-containing esters, chain carbonates, and cyclic carbonates, along with non-fluorine-containing carbonates, to enhance safety, discharge capacity, and cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fluorine-containing non-aqueous electrolytic solution is used, then incombustibility (safety) is improved, but discharge capacity and rate characteristics deteriorate
Solution Approach 1:
The patent uses a composite electrolyte system combining fluorine-containing cyclic carbonate (providing safety and incombustibility) with non-fluorine-containing chain carbonate and cyclic carbonate (providing high discharge capacity and rate characteristics). This composite approach allows the electrolyte to simultaneously achieve both safety and performance requirements that cannot be met by a single solvent type alone.
Solution Approach 2:
The patent optimizes the compositional parameters of the electrolyte by specifying precise volume ratio ranges: fluorine-containing cyclic carbonate at 10-40%, non-fluorine-containing chain carbonate at 30-70%, and non-fluorine-containing cyclic carbonate at 10-40%. By adjusting these parameters within defined ranges, the electrolyte achieves balanced performance in both safety and discharge characteristics.
2Reliability
If a fluorine-containing non-aqueous electrolytic solution is used, then incombustibility (safety) is improved, but cycle characteristics deteriorate
Solution Approach 1:
The composite electrolyte system combines fluorine-containing cyclic carbonate (for safety) with non-fluorine-containing carbonates (for cycle stability). The non-fluorine-containing cyclic carbonate specifically contributes to improved cycle characteristics through stable SEI formation, while the fluorine-containing component maintains incombustibility, achieving both goals simultaneously.
Solution Approach 2:
The patent specifies optimized concentration ranges for each electrolyte component to achieve both safety and cycle stability. The fluorine-containing cyclic carbonate is maintained at 10-40% to ensure incombustibility while the non-fluorine-containing cyclic carbonate at 10-40% provides cycle stability, demonstrating how parameter optimization resolves the contradiction between safety and durability.
3Reliability
If a fluorine-containing non-aqueous electrolytic solution is used, then incombustibility (safety) is improved, but rate characteristics deteriorate
Solution Approach 1:
The electrolyte combines fluorine-containing cyclic carbonate (providing safety) with non-fluorine-containing chain carbonate (providing low viscosity and high ionic conductivity for fast charge-discharge rates). The non-fluorine-containing chain carbonate reduces overall electrolyte viscosity and improves ion transport kinetics, enabling high rate characteristics while the fluorine-containing component maintains incombustibility.
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 proposed solution significantly improves discharge capacity, rate characteristics, and cycle characteristics while ensuring improved incombustibility and safety, making the lithium secondary cell more efficient and reliable.
Implementation Method 1
the non-aqueous electrolytic solution comprises an electrolyte salt and a solvent for dissolving the electrolyte salt
Implementation Method 2
a lithium secondary cell comprising a negative electrode, a non-aqueous electrolytic solution and a positive electrode
Data Source
Figure 1
AI summary
There is provided a lithium secondary cell having specifically excellent discharge capacity, rate characteristics and further cycle characteristics and improved incombustibility (safety). The lithium secondary cell comprises a negative electrode, a non-aqueous electrolytic solution and a positive electrode, in which an active material for the negative electrode comprises lithium titanate and the non-aqueous electrolytic solution comprises a fluorine-containing solvent.