Fluorinated Ionic Liquid Electrolyte for Battery Safety
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Solution Overview
Problem
Lithium secondary batteries face issues with thermal instability and safety due to metal component release, leading to swelling and reduced lifespan, and the addition of high amounts of ionic liquids for flame retardancy results in increased irreversible capacity and side reactions with graphite.
Innovation Solution
An ionic liquid comprising specific N-containing heterocyclic cationic and anionic compounds, used in combination with a lithium salt and solvent, is added to the electrolyte in a concentration of 3-10 wt%, along with a negative electrode protective film former, to enhance flame retardancy while reducing irreversible capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If 20 wt% or more of ionic liquid is added to secure flame retardant properties, then flame retardancy is improved, but initial irreversible capacity becomes significantly high due to side reaction of graphite
Solution Approach 1:
The patent changes the chemical structure parameters of the ionic liquid by introducing fluorinated alkyl chains with specific lengths (m+n=3 to 18) and ratios (0.2 ≤ n/(m+n) ≤ 0.8). This structural optimization allows the ionic liquid to achieve flame retardancy at lower concentrations (1-20 wt%) while reducing side reactions with graphite, thereby lowering initial irreversible capacity compared to conventional ionic liquids requiring 20 wt% or more
Solution Approach 2:
The patent creates a composite electrolyte system combining the fluorinated ionic liquid with lithium salt and solvent. This composite approach synergistically enhances flame retardancy while the specific fluorinated structure minimizes harmful side reactions, resolving the contradiction between safety and energy loss
2Object-affected harmful factors
If high amount of ionic liquid is added to improve flame retardancy, then safety is improved, but side reaction with graphite increases making it impossible to drive secondary battery cell
Solution Approach 1:
The patent optimizes the chemical parameters of the ionic liquid by using fluorinated alkyl chains with controlled carbon numbers (m+n=3 to 18) and specific fluorine content ratios (0.2 ≤ n/(m+n) ≤ 0.8). These parameter changes enhance flame retardancy while minimizing side reactions with graphite, enabling battery operation even at 1-20 wt% concentration where conventional ionic liquids fail
Solution Approach 2:
The patent uses conventional ionic liquid structures as a template and introduces fluorine substitution to create an improved version that retains flame retardant properties while adding resistance to side reactions, allowing the battery to remain drivable
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 improves flame retardancy and reduces irreversible capacity, delaying explosion in high-temperature tests and maintaining sufficient battery performance, as demonstrated by comparative examples.
Implementation Method 1
an initial protective film is formed on a surface of the negative electrode in a preliminary step prior to charging and discharging of the secondary battery
Implementation Method 2
oxygen released from the positive electrode may accelerate an exothermic decomposition reaction of an electrolyte solvent
Data Source
Figure 1(a)~1(d)
AI summary
Provided is an ionic liquid including a cationic compound represented by Formula (1), where R represents an N-containing heterocyclic cation, and an anionic compound, an electrolyte including the ionic liquid, and a secondary battery.