LLZO Solid Electrolyte Separator with Fluoride-Treated Surface Passivation
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Solution Overview
Problem
Solid-state batteries face challenges such as interfacial delamination and loss of contact area due to volume changes of anode and cathode during charging and discharging, and lithium lanthanum zirconium oxide (LLZO) is sensitive to moisture, forming a passivation layer that compromises ionic conductivity.
Innovation Solution
A method involving coating LLZO powder with aluminum fluoride to create a fluoride-treated powder, followed by a solid-state reaction to form aluminum oxide and lithium fluoride, which is then sintered under pressure to stabilize the cubic phase and enhance ionic conductivity, using a sintering aid like lithium fluoride to reduce temperature and densify the electrolyte separator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If LLZO powder is exposed to air, then lithium carbonate passivation layer forms on the surface, but ionic conductivity is compromised
Solution Approach 1:
The patent converts the harmful lithium carbonate passivation layer into a beneficial component by reacting it with aluminum fluoride during solid-state reaction to form aluminum oxide dopant and lithium fluoride sintering aid. The reaction transforms the harmful surface layer into substances that stabilize the cubic phase and enhance ionic conductivity, particularly at grain boundaries.
Solution Approach 2:
Aluminum fluoride serves as an intermediary substance that reacts with the lithium carbonate passivation layer during solid-state reaction. This intermediary reaction produces aluminum oxide and lithium fluoride, which then act as dopant and sintering aid respectively, resolving the conductivity issue caused by the original passivation layer.
2Reliability
If sintering temperature is increased to densify the electrolyte separator, then ionic conductivity is enhanced, but energy consumption and material degradation increase
Solution Approach 1:
The patent changes the chemical composition parameters of the sintering mixture by incorporating aluminum fluoride that reacts to form lithium fluoride. This compositional change enables effective sintering at lower temperatures (reducing energy consumption) while still achieving the necessary densification and ionic conductivity enhancement.
Solution Approach 2:
Lithium fluoride acts as a sintering aid intermediary that facilitates densification at lower temperatures. It modifies the sintering process to achieve effective packing and bonding of LLZO particles without requiring the high temperatures that would increase energy consumption and cause material degradation.
3Stability of the object's composition
If aluminum fluoride is added to react with lithium carbonate layer, then aluminum oxide dopant is formed to stabilize cubic phase, but additional processing steps are required
Solution Approach 1:
The patent merges multiple functions into a single solid-state reaction step: the aluminum fluoride simultaneously reacts with lithium carbonate to form aluminum oxide dopant (for cubic phase stabilization) and lithium fluoride sintering aid. This combined approach achieves compositional stabilization and sintering enhancement in one integrated process rather than separate steps.
Solution Approach 2:
Aluminum fluoride serves multiple functions: it reacts with the harmful lithium carbonate passivation layer, produces aluminum oxide dopant for cubic phase stabilization, and generates lithium fluoride as a sintering aid. This multi-functional additive reduces the need for separate processing steps to achieve each of these objectives.
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 method effectively stabilizes the cubic phase of LLZO, enhances ionic conductivity, and facilitates lithium-ion diffusion through grain boundaries, improving the performance and durability of the solid electrolyte separator.
Implementation Method 1
operating a solid-state reaction upon the fluoride-treated garnet-based material powder, such that the aluminum fluoride reacts with the lithium carbonate layer to create aluminum oxide, carbon dioxide, and lithium fluoride
Implementation Method 2
The sintering includes applying pressure upon the fluoride-treated and solid-state reacted garnet-based material powder to densify the fluoride-treated and solid-state reacted garnet-based material powder
Implementation Method 3
sintering further includes heating the fluoride-treated and solid-state reacted garnet-based material powder to a temperature of 1050° C. for 1 hour under a pressure of 80 megapascals
Implementation Method 4
sintering further includes utilizing the lithium fluoride as a sintering aid, thereby enabling a relatively lower minimum temperature during the sintering
Data Source
AI summary
A method to create a garnet-based solid electrolyte separator for a battery cell is provided. The method includes coating a garnet-based material powder, initially including a lithium carbonate layer upon an outer surface of the garnet-based material powder, with aluminum fluoride to create a fluoride-treated garnet-based material powder. The method further includes operating a solid-state reaction upon the fluoride-treated garnet-based material powder, such that the aluminum fluoride reacts with the lithium carbonate layer to create aluminum oxide, carbon dioxide, and lithium fluoride. The solid-state reaction creates a fluoride-treated and solid-state reacted garnet-based material powder including the aluminum oxide and the lithium fluoride. The method further includes sintering the fluoride-treated and solid-state reacted garnet-based material powder including the aluminum oxide and the lithium fluoride. The sintering includes applying pressure upon the fluoride-treated and solid-state reacted garnet-based material powder to densify the powder and create the separator.