Lithium-Sulfur Cathode Slurry and Electrolyte for Polysulfide Control
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Solution Overview
Problem
Conventional lithium-sulfur secondary batteries face challenges in suppressing lithium polysulfide elution, leading to decreased battery capacity and lifetime due to low electrical conductivity and reactivity of sulfur, which affects energy density and stability.
Innovation Solution
A lithium secondary battery design incorporating a positive electrode slurry with a controlled particle size of 15 µm to 50 µm and an electrolyte liquid with a solvent having a dipole moment per unit volume (DV2) factor of 1.75 or less, utilizing a sulfur-carbon composite and a fluorinated ether-based solvent to enhance conductivity and reduce polysulfide elution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional lithium-sulfur secondary batteries use sulfur-based material as positive electrode active material to achieve high theoretical energy density, then energy density is improved, but lithium polysulfide elution occurs leading to decreased battery capacity and lifetime
Solution Approach 1:
A coating layer comprising a nitrogen-containing heterocyclic compound is formed on the sulfur-based material to act as an intermediary barrier. This coating layer prevents direct contact between lithium polysulfide and the electrolyte liquid, thereby suppressing polysulfide elution while maintaining the high energy density benefits of sulfur-based cathodes.
Solution Approach 2:
The invention changes the chemical composition and surface properties of the positive electrode active material by introducing a nitrogen-containing heterocyclic compound coating. This parameter change modifies the interface between sulfur-based material and electrolyte, reducing polysulfide dissolution and improving battery lifetime without sacrificing energy density.
2Reliability
If sulfur-based material is used in solid-state form to improve electrical conductivity, then conductivity is improved, but reactivity with electrons and lithium ions becomes difficult to secure
Solution Approach 1:
The invention changes the surface chemical properties of sulfur-based material by coating it with a nitrogen-containing heterocyclic compound. This creates an intermediate layer that facilitates electron and lithium ion transfer while maintaining the inherent conductivity advantages of solid-state sulfur.
Solution Approach 2:
The positive electrode active material becomes a composite structure combining sulfur-based material with a nitrogen-containing heterocyclic compound coating. This composite structure provides both the electrical conductivity of solid-state sulfur and the reactivity enhancement from the nitrogen-containing coating layer.
3Ease of operation
If ether-based solvent with high solubility for lithium polysulfide is used to improve reactivity, then reactivity is improved, but lithium polysulfide concentration increases in electrolyte liquid causing side reactions
Solution Approach 1:
The nitrogen-containing heterocyclic compound coating acts as an intermediary barrier that prevents lithium polysulfide from dissolving into the electrolyte liquid while still allowing necessary electrochemical reactions to occur at the electrode surface. This eliminates the harmful side reactions associated with high polysulfide concentration in the electrolyte.
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 battery achieves improved energy density and lifetime properties by minimizing polysulfide elution, maintaining high sulfur loading and reducing electrolyte liquid content, thereby enhancing overall performance.
Implementation Method 1
a coating layer comprising a nitrogen-containing heterocyclic compound on the sulfur-based material
Implementation Method 2
lithium, a negative electrode active material, is oxidized while releasing electrons and being ionized
Implementation Method 3
The lithium cation produced through the oxidation reaction of lithium is transferred to a positive electrode through an electrolyte
Implementation Method 4
a sulfur-based material, a positive electrode active material, is reduced by receiving the electrons
Data Source
Figure 1
AI summary
The present invention relates to a lithium secondary battery, and in particular, to a lithium secondary battery capable of obtaining high energy density and long lifetime compared to conventional lithium secondary batteries by including positive electrode slurry having a particle size (based on D50) of 15 µm to 50 µm and specifying a condition of an electrolyte liquid.