Lithium-Sulfur Cathode Slurry and Electrolyte for Longer Cycle Life
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Solution Overview
Problem
Conventional lithium-sulfur secondary batteries face issues with lithium polysulfide elution, leading to decreased battery capacity and lifetime due to low electrical conductivity of sulfur and reactivity with electrons, which are not adequately addressed by existing materials and structures.
Innovation Solution
A lithium secondary battery design featuring a positive electrode with a sulfur-carbon composite slurry of controlled particle size (15 μm to 50 μm) and an electrolyte liquid with a solvent having a dipole moment per unit volume (DV2) of 1.75 or less, combined with 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 as a 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 diaphragm is introduced as an intermediary component between the positive and negative electrodes. This diaphragm selectively blocks lithium polysulfide molecules from migrating to the negative electrode while allowing lithium ions to pass through, thereby preventing polysulfide elution and improving battery reliability without compromising energy density
Solution Approach 2:
The diaphragm is functionalized with specific chemical groups or structures that create localized regions with high affinity for lithium polysulfide. This local quality enhancement allows the diaphragm to selectively adsorb and retain polysulfides at specific locations, preventing their migration while maintaining overall battery performance
2Reliability
If sulfur-carbon nanotube composite is used to prevent lithium polysulfide elution, then battery lifetime is improved, but manufacturing complexity increases
Solution Approach 1:
The invention extracts and separates the polysulfide blocking function from the electrode structure itself by introducing a standalone diaphragm component. This allows the sulfur-carbon nanotube composite to be used in a simpler configuration without requiring complex integrated structures, thereby reducing manufacturing complexity while maintaining improved battery lifetime
Solution Approach 2:
The diaphragm serves multiple functions: it acts as a physical separator, a selective barrier for polysulfide, and an ion-conducting pathway. This multi-functionality eliminates the need for additional complex components or structures, simplifying the overall manufacturing process while achieving improved battery reliability
3Reliability
If sulfur-including graphene composite with pores is used as positive electrode active material, then lithium polysulfide elution is suppressed, but manufacturing precision requirements increase
Solution Approach 1:
The invention segments the polysulfide retention function from the electrode material by using a separate diaphragm component. This eliminates the need to create precise pores in the sulfur-including graphene composite during manufacturing, thereby reducing manufacturing precision requirements while still achieving effective polysulfide elution suppression through the diaphragm's selective blocking capability
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 design improves energy density and lifetime properties by minimizing polysulfide elution, maintaining high sulfur loading and reducing side reactions, resulting in enhanced battery performance.
Implementation Method 1
a solvent having a dipole moment per unit volume (DV2) of 1.75 or less
Implementation Method 2
μ is viscosity of the solvent (cP, 25° C.)
Implementation Method 3
Due to low electrical conductivity of sulfur, a positive electrode active material
Implementation Method 4
the oxidation reaction of lithium is a process in which lithium metal releases electrons and changes into a lithium cation form
Implementation Method 5
The lithium cation produced through the oxidation reaction of lithium is transferred to a positive electrode through an electrolyte
Implementation Method 6
the reduction reaction of sulfur is a process in which a sulfur-sulfur bond receives two electrons and changes into a sulfur anion form
Implementation Method 7
forms a salt by bonding with the sulfur anion produced through the reduction reaction of sulfur
Data Source
AI summary
Disclosed is a lithium secondary battery, and in particular, 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.