LiFSI Electrolyte for Stable SEI Film Formation

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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, along with a lithium-nickel-manganese-cobalt-based oxide positive electrode active material, is used to form a stable SEI film, suppressing gas generation and decomposition, and optimizing the lithium salt and LiFSI concentration for improved performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If liquid electrolyte additives are not included or are included in insufficient amounts, then manufacturing complexity is reduced, but low temperature output property is poor due to non-uniform SEI film formation

Engineering Contradiction:

Improveelectrolyte composition complexityVSAvoidlow temperature output property

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent optimizes the concentration parameters of LiFSI (0.01-2 mol/L) and fluorinated benzene-based compound (1-20 wt%) in the electrolyte to achieve uniform SEI film formation at low temperatures, improving output properties without excessive complexity

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent combines LiFSI and fluorinated benzene-based compound as a composite additive system in the electrolyte, where the synergistic interaction between these components enables uniform SEI film formation and improves low temperature output performance

Inventive Principle:

Principle #40Composite materials

2Reliability

If liquid electrolyte additives are included in excessive amounts, then low temperature output property is improved, but positive electrode surface decomposition occurs at high temperature

Engineering Contradiction:

Improvelow temperature output propertyVSAvoidpositive electrode surface stability

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent precisely controls the concentration of LiFSI (0.01-2 mol/L) and fluorinated benzene-based compound (1-20 wt%) to achieve the optimal balance where sufficient SEI film uniformity is obtained without causing positive electrode surface decomposition at high temperatures

Inventive Principle:

Principle #35Parameter changes

3Reliability

If liquid electrolyte additives are included in improper amounts, then low temperature output property may be improved, but oxidation reaction occurs and irreversible capacity increases

Engineering Contradiction:

Improvelow temperature output propertyVSAvoidirreversible capacity

Core Design Contradiction:

ReliabilityVSLoss of substance

Solution Approach 1:

The patent optimizes the concentration parameters of LiFSI (0.01-2 mol/L) and fluorinated benzene-based compound (1-20 wt%) to achieve uniform SEI film formation that prevents oxidation reactions and minimizes irreversible capacity loss

Inventive Principle:

Principle #35Parameter changes

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 enhances low temperature and room temperature outputs, stability, and high temperature storage properties by forming a stable SEI film, preventing positive electrode decomposition and oxidation reactions, thereby improving battery performance and safety.

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. This ion tunnel solvates lithium ions and performs a role of preventing the collapse of the carbon negative electrode structure

Methodology Applied

Scientific EffectIon tunneling:

Implementation Method 3

Such a lithium secondary battery experiences charge and discharge while repeating intercalation and deintercalation of lithium ions from a lithium metal oxide of a positive electrode to a graphite electrode of a negative electrode

Methodology Applied

Scientific EffectIntercalation:

Data Source

PatentUS10276894B2Non-aqueous liquid electrolyte and lithium secondary battery comprising the same

Publication Date: 2019.04.30 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.