LiFSI and Fluorinated Benzene Electrolyte for Stable SEI Film

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Solution Overview

Problem

Lithium secondary batteries face challenges in enhancing low temperature, room temperature, and high temperature output properties, capacity, and stability due to non-uniform solid electrolyte interface (SEI) film formation and decomposition of positive electrode surfaces in existing liquid electrolytes.

Innovation Solution

A non-aqueous liquid electrolyte comprising lithium bis(fluorosulfonyl)imide (LiFSI) and a fluorinated benzene-based compound, combined with a lithium-nickel-manganese-cobalt-based oxide positive electrode active material, forms a stable SEI film on the negative electrode, suppressing gas generation and decomposition, and optimizing the concentration of LiFSI and lithium salts to prevent side reactions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If existing liquid electrolyte additives are used, then low temperature output property enhancement is expected, but a non-uniform SEI film is formed

Engineering Contradiction:

Improvelow temperature output propertyVSAvoidSEI film uniformity

Core Design Contradiction:

PowerVSStability of the object's composition

Solution Approach 1:

The patent changes the chemical composition parameters of the electrolyte by introducing LiFSI and fluorinated benzene-based compound additives. This parameter change enables the formation of a uniform SEI film while maintaining low temperature output properties, resolving the contradiction between power performance and film uniformity.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses a composite electrolyte additive system combining LiFSI (lithium bis(fluorosulfonyl)imide) and fluorinated benzene-based compounds. This composite approach creates synergistic effects that produce uniform SEI films with good low temperature performance, overcoming the limitations of single additives.

Inventive Principle:

Principle #40Composite materials

2Power

If liquid electrolyte additives are added to enhance output, then low temperature performance improves, but positive electrode surface decomposition occurs at high temperature

Engineering Contradiction:

Improveoutput propertyVSAvoidhigh temperature stability

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent optimizes the concentration parameters of electrolyte additives, specifically using LiFSI at 0.01-5 wt% and fluorinated benzene-based compounds at 0.1-5 wt%. This precise parameter control enables the electrolyte to provide good output performance at low temperatures while preventing positive electrode decomposition at high temperatures through controlled SEI formation and reduced electrolyte reactivity.

Inventive Principle:

Principle #35Parameter changes

3Power

If electrolyte additives are used to improve output, then low temperature performance enhances, but oxidation reaction increases and irreversible capacity rises

Engineering Contradiction:

Improveoutput propertyVSAvoidirreversible capacity

Core Design Contradiction:

PowerVSLoss of energy

Solution Approach 1:

The patent converts the potential harmful oxidation reactions into beneficial effects by using fluorinated benzene-based compounds that preferentially react to form protective SEI films. These films prevent further oxidation of the electrolyte and reduce irreversible capacity loss, transforming what would be harmful side reactions into protective mechanisms that improve overall battery performance and reduce energy loss.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 output properties and stability at low and high temperatures, reduces irreversible capacity, and enhances battery safety by forming a thin, stable SEI film and preventing positive electrode decomposition, while maintaining efficient lithium ion migration.

Implementation Method 1

the lithium reacts with a carbon electrode due to high reactivity, and forms a film on the negative electrode surface by producing Li2CO3, LiO, LiOH and the like. Such a film is referred to as a solid electrolyte interface (SEI) film

Methodology Applied

Scientific EffectSolid electrolyte interface (SEI) film formation:

Implementation Method 2

the SEI film performs a role of an ion tunnel and passes only lithium ions

Methodology Applied

Scientific EffectIon tunneling:

Implementation Method 3

This ion tunnel solvates lithium ions and performs a role of preventing the collapse of the carbon negative electrode structure by a high molecular weight organic solvent of a liquid electrolyte moving together being co-intercalated to the carbon negative electrode

Methodology Applied

Scientific EffectSolvation: Solvation

Data Source

PatentUS11437646B2Non-aqueous liquid electrolyte and lithium secondary battery comprising the same

Publication Date: 2022.09.06 LG ENERGY SOLUTION LTD

AI summary

The present invention provides a lithium secondary battery comprising a non-aqueous liquid electrolyte comprising lithium bis(fluorosulfonyl)imide (LiFSI) and a fluorinated benzene-based compound as additives, a positive electrode comprising a lithium-nickel-manganese-cobalt-based oxide as a positive electrode active material, a negative electrode, and a separator. With the non-aqueous liquid electrolyte for a lithium secondary battery of the present invention, a solid SEI film is formed on a negative electrode when initially charging a lithium secondary battery comprising the non-aqueous liquid electrolyte, and an output property of the lithium secondary battery is improved, and an output property and stability after high temperature storage are capable of being enhanced as well.