Solid-State Sulfur Cathode Electrolyte for Polysulfide Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Secondary batteries with sulfur-based positive active materials face issues such as the elution of lithium polysulfide, which leads to decreased capacity and increased internal resistance, and disconnection of ion transfer paths due to volume changes during charging and discharging, resulting in deteriorated cycle characteristics and lifespan.
Innovation Solution
An all-solid secondary battery design featuring a lithium-containing sulfide-based positive active material and a composite electrolyte comprising a polymer, lithium salt, and an ionic liquid with saturated solubility of lithium polysulfide of 5 wt% or less, inhibiting elution and migration of lithium polysulfide and maintaining a stable ion transfer path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a sulfur-based material is used as a positive active material to increase capacity, then the battery capacity increases, but lithium polysulfide elution occurs leading to decreased capacity and increased internal resistance
Solution Approach 1:
A solid electrolyte layer is introduced as an intermediary between the positive electrode containing sulfur-based material and the negative electrode. This solid electrolyte layer acts as a physical barrier that prevents lithium polysulfide from eluting into the electrolyte, thereby maintaining battery capacity and internal resistance stability over charge-discharge cycles while still allowing lithium ion transport.
Solution Approach 2:
The positive electrode is designed as a composite structure combining sulfur-based positive active material with a solid electrolyte layer. This composite material approach enables the system to simultaneously achieve high capacity from the sulfur material while the integrated solid electrolyte component prevents polysulfide dissolution, resolving the contradiction between capacity and reliability.
2Quantity of substance
If a sulfur-based material is used as a positive active material, then the battery capacity increases, but disconnection of ion transfer path occurs due to volume change during charging and discharging
Solution Approach 1:
The solid electrolyte layer functions as a flexible interface that can accommodate the volume expansion and contraction of the sulfur-based positive active material during charge-discharge cycles. This flexible film structure maintains continuous contact and prevents disconnection of the ion transfer path while allowing the sulfur material to undergo its necessary volume changes for high capacity operation.
3Quantity of substance
If lithium polysulfide dissolves in the electrolyte, then the concentration increases during charging and discharging, but the positive active material content decreases leading to capacity loss
Solution Approach 1:
The harmful effect of lithium polysulfide dissolution is extracted and isolated by introducing a solid electrolyte layer that physically separates the sulfur-based positive active material from the liquid electrolyte. This extraction prevents lithium polysulfide from entering the electrolyte solution, thereby preventing capacity loss while allowing the battery to operate with high sulfur content for increased 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
This design effectively prevents the decrease in capacity and increase in internal resistance, improving the cycle characteristics and lifespan of the battery by maintaining a stable ion transfer path and compensating for volume changes in the positive active material.
Implementation Method 1
a solid electrolyte layer provided between the positive electrode layer and the negative electrode layer... effectively prevents the decrease in capacity and increase in internal resistance
Implementation Method 2
the composite electrolyte includes a polymer, a lithium salt, and an ionic liquid, wherein the ionic liquid has a saturated solubility of lithium polysulfide of 5 wt % or less at 25° C.
Implementation Method 3
maintaining a stable ion transfer path... improving the cycle characteristics and lifespan of the battery by maintaining a stable ion transfer path
Data Source
AI summary
An all-solid secondary battery including a positive electrode layer including a positive current collector and a positive active material layer on one or more surfaces of the positive current collector is provided. The battery includes a negative electrode layer and a solid electrolyte layer between the positive electrode layer and the negative electrode layer. The positive active material layer includes a composite electrolyte and a lithium-containing sulfide-based positive active material including Li2S and/or a Li2S— containing composite. The composite electrolyte includes a polymer, a lithium salt, and an ionic liquid having a saturated solubility of lithium polysulfide of 5 wt % or less at 25° C.