Sulfur Core-Shell Cathode for Lithium-Sulfur Battery Polysulfide Confinement

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Solution Overview

Problem

Lithium-sulfur batteries face limitations due to the poor conductivity of sulfur and the migration of polysulfides, leading to decreased utilization, self-discharge, and reduced cycleability, as well as mechanical degradation from volume expansion and contraction of sulfur-based cathodes during charging/discharging.

Innovation Solution

A sulfur-based active material with a core-shell structure, where sulfur is confined within a hollow core surrounded by a nitrogen-doped porous carbon shell, immobilizing polysulfides and enhancing conductivity through a polymer shell coating that includes nitrogen atoms bonding with carbon atoms, thereby improving the connection between sulfur and the carbon shell.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If sulfur is used as the active material in lithium-sulfur batteries, then high energy density is achieved, but poor conductivity and polysulfide migration occur leading to decreased utilization and reduced cycleability

Engineering Contradiction:

Improveenergy densityVSAvoidcycleability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent employs a nested core-shell structure where sulfur is confined within a hollow core, which is itself enclosed by a porous carbon shell. This multi-layer nesting approach effectively isolates sulfur while maintaining its electrochemical activity, thereby preventing polysulfide migration and improving cycleability without compromising energy density

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The patent utilizes composite materials by combining sulfur with a porous carbon shell containing nitrogen atoms. This composite structure leverages the high energy density of sulfur while the nitrogen-doped carbon shell provides enhanced conductivity and structural stability, resolving the contradiction between energy density and cycleability

Inventive Principle:

Principle #40Composite materials

2Duration of action of moving object

If sulfur-based cathodes undergo charging and discharging, then battery operation is enabled, but volume expansion and contraction cause mechanical degradation

Engineering Contradiction:

Improvebattery operationVSAvoidmechanical strength

Core Design Contradiction:

Duration of action of moving objectVSStrength

Solution Approach 1:

The patent employs a flexible porous carbon shell that can accommodate the volume expansion and contraction of sulfur during charging and discharging cycles. This flexible shell structure maintains mechanical integrity while allowing the sulfur core to undergo volumetric changes, thereby enabling sustained battery operation without mechanical degradation

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The hollow core design provides beforehand cushioning by creating empty space within the shell that can absorb the volume expansion of sulfur during lithiation. This pre-designed cushioning space prevents mechanical stress from being transmitted to the shell structure, maintaining strength over multiple cycles

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Productivity

If polysulfides are allowed to migrate during battery operation, then electrochemical reactions proceed, but self-discharge and decreased utilization occur

Engineering Contradiction:

Improveelectrochemical reactivityVSAvoidself-discharge

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent applies local quality by creating a nitrogen-doped porous carbon shell with specific local properties around the sulfur core. The nitrogen atoms are locally concentrated at the carbon-sulfur interface, providing enhanced catalytic activity for electrochemical reactions while simultaneously creating a hydrophilic environment that traps polysulfides, preventing their migration and reducing self-discharge

Inventive Principle:

Principle #3Local quality

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 effectively confines sulfur, reduces polysulfide migration, enhances ionic conductivity, and improves mechanical strength, leading to increased cycle stability and retention of discharge capacity over multiple cycles.

Implementation Method 1

The polymer shell coating includes nitrogen atoms that bond to carbon atoms of the porous carbon shell so that the porous carbon shell is a nitrogen-doped porous carbon shell

Methodology Applied

Scientific EffectChemical bonding: Chemical Bonding

Data Source

PatentUS9437871B2Sulfur based active material for a positive electrode

Publication Date: 2016.09.06 GM GLOBAL TECHNOLOGY OPERATIONS LLC

AI summary

A sulfur based active material has a core-shell structure including a hollow core and a porous carbon shell surrounding the hollow core. Sulfur is present in a portion of the hollow core. A polymer shell coating is formed on the porous carbon shell. The polymer shell coating includes nitrogen atoms that bond to carbon atoms of the porous carbon shell so that the porous carbon shell is a nitrogen-confused porous carbon shell.