Lithium-Sulfur Cathode Porosity for High Energy Density

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Solution Overview

Problem

Existing lithium-sulfur secondary batteries face challenges in achieving high energy density due to lithium polysulfide elution, which affects battery capacity and lifetime, despite previous attempts to suppress this issue through varying structures or materials of the sulfur-carbon composite used as a positive electrode active material.

Innovation Solution

The lithium secondary battery is designed with a positive electrode containing a sulfur-carbon composite where the specific surface area and conductivity of the carbon material satisfy a certain condition, and the porosity and mass of sulfur per unit area are specifically adjusted, along with an electrolyte liquid comprising a solvent with a high dipole moment and low viscosity, to enhance initial discharge capacity and energy density.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a low content electrolyte liquid is injected to build high energy density, then energy density is improved, but lithium polysulfide concentration increases making normal battery driving difficult due to decreased active material mobility and increased side reaction

Engineering Contradiction:

Improveenergy densityVSAvoidbattery driving performance

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent employs a porous carbon material with specific pore volume (0.075-0.30 cm³/g) and surface area (500-1500 m²/g) to host sulfur. The porous structure provides sufficient space for lithium polysulfide accommodation while maintaining electrolyte distribution, enabling high sulfur loading without excessive polysulfide concentration that would hinder battery performance.

Inventive Principle:

Principle #31Porous materials

Solution Approach 2:

The patent uses a sulfur-carbon composite material where sulfur is incorporated into the porous carbon matrix. This composite structure combines the high capacity of sulfur with the conductive and structural benefits of porous carbon, achieving high energy density while preventing polysulfide elution and maintaining good ionic conductivity for reliable battery operation.

Inventive Principle:

Principle #40Composite materials

2Reliability

If various structures or materials of sulfur-carbon composite are used to suppress lithium polysulfide elution, then battery capacity and lifetime are improved, but energy density remains insufficient

Engineering Contradiction:

Improvebattery capacity and lifetimeVSAvoidenergy density

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent optimizes specific parameters of the porous carbon material including pore volume (0.075-0.30 cm³/g), specific surface area (500-1500 m²/g), and sulfur content (30-80 wt%). By precisely controlling these parameters, the patent achieves both effective polysulfide retention for good capacity and lifetime, and high sulfur loading for high energy density.

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

This configuration results in a lithium-sulfur secondary battery with enhanced initial discharge capacity and high energy density, while minimizing detachment during the positive electrode preparation process.

Implementation Method 1

a first solvent in which a DV 2 factor value represented by Mathematical Formula 4 is 0.8 or less: DV 2=DV 2(D·mol/L), wherein DV is a dipole moment per unit volume (D·mol/L)

Methodology Applied

Scientific EffectDipole moment: Dielectric

Implementation Method 2

μ is viscosity of the solvent (cP, 25°C)

Methodology Applied

Scientific EffectViscosity: Viscometer

Implementation Method 3

conductivity is electrical conductivity obtained by converting a powder resistance value measured while applying a pressure of 2000 kgf to the carbon material to conductivity

Methodology Applied

Scientific EffectElectrical conductivity: Conduction (electrical)

Implementation Method 4

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

Methodology Applied

Scientific EffectIon transport: Electrolyte

Implementation Method 5

the reduction reaction of sulfur is a process in which a sulfur-sulfur bond receives two electrons and changes into a sulfur anion form

Methodology Applied

Scientific EffectReduction reaction: Reduction

Implementation Method 6

the oxidation reaction of lithium is a process in which lithium metal releases electrons and changes into a lithium cation form

Methodology Applied

Scientific EffectOxidation reaction: Oxidation

Data Source

PatentEP3863089B1Lithium secondary battery

Publication Date: 2026.04.01 LG ENERGY SOLUTION LTD

Figure 1

AI summary

The present invention relates to a lithium secondary battery. More specifically, in the lithium secondary battery, by specifically adjusting the porosity (%) and the mass of sulfur per unit area (mg/cm2) of a positive electrode active material layer including a sulfur-carbon composite, the initial battery discharge capacity is improved, and thus a high energy density can be achieved.