Solid-State Battery Cathode Electrolyte for Polysulfide Suppression

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Solution Overview

Problem

Lithium polysulfide elution and volume change in sulfur-based positive active materials lead to decreased capacity, increased resistance, and deteriorated lifespan in secondary batteries, necessitating a solution to inhibit ion transfer path disconnection and reduce side reactions.

Innovation Solution

An all-solid secondary battery design incorporating a lithium-containing sulfide-based positive active material with a composite electrolyte comprising a polymer, lithium salt, and an ionic liquid with low lithium polysulfide solubility, which inhibits lithium polysulfide elution and maintains ion transfer paths during charging and discharging.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If a sulfur-based material is used as a positive active material to increase capacity, then the battery capacity increases, but lithium polysulfide elutes during charging and discharging causing capacity decrease and lifespan deterioration

Engineering Contradiction:

Improvebattery capacityVSAvoidlifespan characteristics

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

A coating layer comprising a sulfide compound is formed on the surface of the sulfur-based positive active material particles. This coating layer acts as an intermediary barrier that prevents direct contact between the lithium polysulfide and the electrolyte, thereby suppressing polysulfide elution while maintaining the high capacity benefits of sulfur-based materials

Inventive Principle:

Principle #24Intermediary (Mediator)

2Quantity of substance

If a sulfur-based material is used as a positive active material, then capacity increases, but the volume change during charging and discharging causes disconnection of ion transfer paths

Engineering Contradiction:

Improvebattery capacityVSAvoidion transfer path connectivity

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

A coating layer comprising a sulfide compound is formed on the surface of the sulfur-based positive active material particles. This coating layer acts as a flexible protective shell that can accommodate the volume expansion and contraction of the sulfur particles during charging and discharging cycles, maintaining continuous contact and preventing disconnection of ion transfer paths

Inventive Principle:

Principle #30Flexible shells and thin films

3Use of energy by moving object

If lithium polysulfide is produced during charging and discharging, then electrochemical reactions occur, but the high solubility of lithium polysulfide in electrolyte causes rapid concentration increase and capacity decrease

Engineering Contradiction:

Improveelectrochemical reactivityVSAvoidpositive active material content

Core Design Contradiction:

Use of energy by moving objectVSQuantity of substance

Solution Approach 1:

A coating layer comprising a sulfide compound is formed on the surface of the sulfur-based positive active material particles. This coating layer acts as an intermediary barrier that suppresses the dissolution of lithium polysulfide into the electrolyte by preventing direct contact between the polysulfide and electrolyte, thereby maintaining positive active material content and capacity

Inventive Principle:

Principle #24Intermediary (Mediator)

4Use of energy by moving object

If side reactions occur between polysulfide and negative active material, then electrochemical processes continue, but lifespan characteristics deteriorate

Engineering Contradiction:

Improveelectrochemical reactivityVSAvoidlifespan characteristics

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

A coating layer comprising a sulfide compound is formed on the surface of the sulfur-based positive active material particles. This coating layer acts as an intermediary barrier that prevents side reactions between lithium polysulfide and the negative active material by blocking the migration path of polysulfide, thereby improving lifespan characteristics while maintaining electrochemical reactivity

Inventive Principle:

Principle #24Intermediary (Mediator)

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 effectively prevents lithium polysulfide elution, maintains ion transfer paths, and improves cycle characteristics and lifespan by reducing internal resistance and side reactions.

Implementation Method 1

the ionic liquid has a saturated solubility of lithium polysulfide of 5 wt% or less at 25 °C

Methodology Applied

Scientific EffectSolubility: Solvation

Data Source

PatentEP4435887B1All-solid secondary battery

Publication Date: 2026.04.29 SAMSUNG SDI CO LTD

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AI summary

An all-solid secondary battery including a positive electrode layer including a positive current collector and a positive active material layer on one or more surfaces of the positive current collector is provided. The battery includes a negative electrode layer and a solid electrolyte layer between the positive electrode layer and the negative electrode layer. The positive active material layer includes a composite electrolyte and a lithium-containing sulfide-based positive active material including Li2S and/or a Li2S-containing composite. The composite electrolyte includes a polymer, a lithium salt, and an ionic liquid having a saturated solubility of lithium polysulfide of 5 wt% or less at 25 °C.