Lithium-Sulfur Battery SEI and Electrolyte Control Against Sulfur Passivation
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Solution Overview
Problem
Lithium-sulfur batteries face challenges in achieving long lifespan due to sulfur passivation on the negative electrode, leading to irreversible loss of active material and reduced capacity, especially during repeated charge and discharge cycles.
Innovation Solution
A lithium-sulfur battery design with a sulfur-carbon composite positive electrode, a lithium-containing layer with a solid electrolyte interphase (SEI) layer on the negative electrode, and a controlled sulfur content of 3 weight % or less, along with an electrolyte solution containing a nitrogen compound, such as lithium nitrate, to minimize sulfur formation and enhance electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If lithium-sulfur batteries use sulfur as the positive electrode active material to achieve high capacity and high energy density, then the theoretical specific capacity reaches 1,675 mAh/g and theoretical energy density reaches 2,600 Wh/kg, but sulfur passivation occurs on the negative electrode during repeated charge and discharge cycles, causing irreversible loss of active material and reducing battery lifespan
Solution Approach 1:
A separator coated with sulfur-phosphorus compound is introduced as an intermediary between the positive and negative electrodes. This coating layer prevents direct contact and interaction between lithium polysulfides and the negative electrode, thereby blocking the passivation process while allowing ion transport. The separator acts as a mediator that eliminates the harmful shuttle effect without compromising the high energy density benefits of lithium-sulfur batteries
Solution Approach 2:
The harmful sulfur passivation effect is extracted and removed from the system by using a separator that specifically targets and prevents polysulfide migration to the negative electrode. The separator design extracts the problematic shuttle effect while retaining the beneficial electrochemical reactions, thus improving lifespan without sacrificing energy density
2Productivity
If lithium (poly)sulfide is produced at the positive electrode during discharging, then the conversion reaction (S8+16Li++16eāā8Li2S) achieves high capacity, but lithium (poly)sulfide dissolves in the electrolyte solution and precipitates on the negative electrode as solid lithium sulfide, causing surface contamination and sulfur passivation
Solution Approach 1:
The sulfur-phosphorus compound coating on the separator converts the harmful polysulfide migration into a beneficial controlled process. The coating selectively interacts with lithium polysulfides to prevent their harmful precipitation on the negative electrode, while still allowing necessary ion transport for capacity delivery. The potential harmful dissolution and precipitation process is transformed into a controlled interface reaction that protects the negative electrode
Solution Approach 2:
The sulfur-phosphorus compound coating serves as an intermediary layer that intercepts lithium polysulfides before they reach the negative electrode. This intermediate barrier prevents the harmful transformation of dissolved polysulfides into solid lithium sulfide precipitates on the negative electrode surface, thereby eliminating sulfur passivation while maintaining capacity
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 extended lifespan with 80% capacity retention after 190 charge/discharge cycles and maintains high energy density, exceeding 300 Wh/kg, by suppressing sulfur passivation and improving electrical conductivity.
Implementation Method 1
a solid electrolyte interphase (SEI) layer formed on at least one surface of the lithium-containing layer
Implementation Method 2
an electrolyte solution containing a nitrogen compound, such as lithium nitrate, to minimize sulfur formation and enhance electrical conductivity
Implementation Method 3
During discharging, the lithium-sulfur batteries undergo reduction reaction in which sulfur accepts electrons at the positive electrode
Data Source
AI summary
A lithium-sulfur battery having a long lifespan and method for manufacturing the same are provided. The lithium-sulfur battery comprises an electrode assembly which comprises a positive electrode including a sulfur-carbon composite, a negative electrode including a lithium-containing layer and a solid electrolyte interphase (SEI) layer on at least one surface of the lithium-containing layer, and a separator between the positive electrode and the negative electrode; and an electrolyte solution, and the negative electrode comprises sulfur element (S) in an amount of 3 weight % or less based on the total weight of the lithium-containing layer and the SEI layer at state of charge of 100%.