Li-Sulfur Battery Electrolyte Additives for Better Cycle Stability

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Solution Overview

Problem

Lithium-sulfur secondary batteries face challenges in cycle performance due to the reactivity and solubility of lithium polysulfides in the electrolyte, which affect the battery's ability to maintain high energy density and stability over multiple charge-discharge cycles.

Innovation Solution

Incorporating a borate-based lithium salt, such as lithium difluoro(oxalato)borate or lithium bis(oxalate)borate, into the electrolyte in specific concentrations (0-1,000 ppm) enhances the interaction with the positive electrode active material, improving cycle performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the content of electrolyte solution is decreased to improve the reactivity of sulfur, then the reactivity of sulfur is improved, but the concentration of lithium polysulfide in the electrolyte solution is increased, making it difficult for the battery to operate normally due to a decrease in the fluidity of the active material and an increase in side reactions

Engineering Contradiction:

Improvereactivity of sulfurVSAvoidside reactions and decreased fluidity

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent changes the chemical composition parameters of the electrolyte by introducing specific additives (lithium fluoride and/or lithium oxide) to modify the electrolyte's interaction with lithium polysulfide. This allows the system to maintain low electrolyte content for improved sulfur reactivity while the additives prevent harmful side reactions and maintain fluidity by controlling polysulfide solubility and precipitation behavior.

Inventive Principle:

Principle #35Parameter changes

2Quantity of substance

If a high-loading, low-porosity electrode is used to achieve high energy density, then the energy density is improved, but the mass transport and reaction efficiency may be reduced

Engineering Contradiction:

Improveenergy densityVSAvoidreaction efficiency

Core Design Contradiction:

Quantity of substanceVSProductivity

Solution Approach 1:

The patent uses lithium fluoride and lithium oxide as intermediary substances that facilitate mass transport and reaction efficiency within the electrode structure. These additives act as mediators that improve ion conductivity and facilitate lithium ion transport through the electrode matrix, enabling high-loading, low-porosity electrodes to maintain both high energy density and adequate reaction efficiency.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If ether-based solvent is used to improve the solubility of lithium polysulfide and reactivity, then the reactivity is improved, but the cycle performance deteriorates due to polysulfide dissolution and side reactions

Engineering Contradiction:

ImprovereactivityVSAvoidcycle performance

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The patent converts the harmful effect of polysulfide dissolution in ether-based solvents into a beneficial effect by using lithium fluoride and lithium oxide additives. These additives promote the formation of solid precipitates from dissolved polysulfides, which then deposit on the electrode surface to form protective layers. This transforms the harmful dissolution process into a beneficial surface modification that improves cycle performance while maintaining the reactivity benefits of ether-based solvents.

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 addition of borate-based lithium salts significantly improves the cycle performance of lithium-sulfur secondary batteries by stabilizing the electrolyte and enhancing the reactivity of sulfur, leading to better energy density and stability.

Implementation Method 1

an ether-based solvent such as dioxolane and dimethoxy ethane, which are highly soluble for lithium polysulfide, is used as a solvent for the electrolyte solution

Methodology Applied

Scientific EffectSolvation: Solvation

Implementation Method 2

The lithium cation produced by the oxidation reaction of lithium is transferred to the positive electrode through the electrolyte

Methodology Applied

Scientific EffectIon transport: Electrolyte

Implementation Method 3

the oxidation reaction of lithium is a process by which lithium metal releases electron and is converted to lithium cation

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 4

the reduction reaction of sulfur is a process by which the S-S bond accepts two electrons and is converted to a sulfur anion

Methodology Applied

Scientific EffectReduction: Reduction

Data Source

PatentEP4117074B1Lithium-sulfur secondary battery comprising electrolyte containing borate-based lithium salt

Publication Date: 2025.12.03 LG ENERGY SOLUTION LTD

AI summary

A lithium-sulfur secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte contains a borate-based lithium salt, and the borate-based lithium salt is lithium difluoro(oxalato)borate, lithium bis(oxalate)borate, or a combination thereof. The borate-based lithium salt is contained in the electrolyte in an amount exceeding 0 ppm and less than 1,000 ppm based on the total weight of the electrolyte. The cycle performance of the lithium-sulfur secondary battery is improved because the lithium-sulfur secondary battery contains specific borate-based lithium salt in the electrolyte.