Garnet Solid Electrolyte Particle Size Control via Segmented Heating
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Solution Overview
Problem
The existing method for producing solid electrolytes results in coarse particles, leading to increased grain boundary resistance and decreased total lithium ion conductivity in solid electrolyte pellets, which hinders the improvement of lithium ion conductivity.
Innovation Solution
A garnet-type solid electrolyte with a compositional formula (Li7−3xGax)(La3−yNdy)Zr2O12−zFz or (Li7−3x+yGax)(La3−yCay)Zr2O12−zFz is produced using a method involving the mixing of raw material solutions, a first heating treatment, and a second heating treatment with lithium fluoride to substitute 1 atom or less of oxygen with fluorine, optimizing the particle size and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat treatment is performed at high temperature (exceeding 1125°C and lower than 1230°C) to produce solid electrolyte, then the solid electrolyte forms with garnet-type or garnet-like crystal structure, but the solid electrolyte becomes coarse particles leading to increased grain boundary resistance
Solution Approach 1:
The heat treatment process is divided into two distinct stages: a first heating treatment at lower temperature (500-650°C) to form a calcined body with fine particles, and a second heating treatment (main firing) at higher temperature (800-1000°C) to develop the garnet-type crystal structure. This segmentation prevents the formation of coarse particles while ensuring proper crystal structure formation, thereby reducing grain boundary resistance.
Solution Approach 2:
The first heating treatment is performed as a preliminary step before the main firing. This preliminary action creates a calcined body with fine particle morphology and appropriate chemical composition, which then serves as the basis for the second heating treatment. This preliminary preparation ensures that when the higher temperature treatment is applied, coarse particles do not form, thus maintaining fine particle characteristics while achieving the desired crystal structure.
2Stability of the object's composition
If heat treatment temperature is increased to ensure complete reaction and crystal structure formation, then the solid electrolyte achieves proper composition, but grain boundary resistance increases due to coarse particle formation
Solution Approach 1:
The compositional development is achieved through segmented heating stages. The first heating treatment at 500-650°C initiates chemical reactions and forms a calcined body with proper elemental distribution. The second heating treatment at 800-1000°C completes the crystal structure formation. This segmentation allows complete reaction and proper composition without requiring excessively high temperatures that would cause coarse particle formation and increased grain boundary resistance.
Solution Approach 2:
The patent changes the temperature parameter in two distinct steps rather than using a single high temperature. The first stage uses 500-650°C and the second stage uses 800-1000°C. This parameter change strategy achieves complete chemical reaction and proper composition while avoiding the formation of coarse particles, thereby maintaining low grain boundary resistance and high lithium ion conductivity.
3Ease of manufacture
If single-stage heat treatment is used to simplify the production process, then the manufacturing process is easier, but coarse particles form leading to high grain boundary resistance
Solution Approach 1:
The production process is segmented into two heat treatment stages with specific temperature ranges and duration parameters. The first heating treatment at 500-650°C forms a calcined body, and the second heating treatment at 800-1000°C develops the garnet-type crystal structure. This segmentation, while adding a process step, provides precise control over particle size and crystal structure, achieving fine particle morphology with low grain boundary resistance that would not be possible with single-stage treatment.
4Stability of the object's composition
If high temperature heat treatment is applied to ensure complete solidification and crystal structure, then the solid electrolyte achieves stable properties, but total lithium ion conductivity decreases due to large grain boundary resistance
Solution Approach 1:
The heat treatment is segmented into two stages: first heating at 500-650°C to form a calcined body with fine particles, and second heating at 800-1000°C to develop the garnet-type crystal structure. This segmentation achieves stable crystal structure and composition while maintaining fine particle morphology, thereby ensuring low grain boundary resistance and high total lithium ion conductivity.
Solution Approach 2:
The temperature parameter is changed in two steps: first at 500-650°C for calcination, then at 800-1000°C for main firing. This parameter change approach ensures complete solidification and stable crystal structure formation while avoiding the formation of coarse particles, thus maintaining high total lithium ion conductivity through reduced grain boundary resistance.
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 approach enhances the bulk lithium ion conductivity and reduces grain boundary resistance, resulting in improved electrochemical properties and lithium ion conduction efficiency.
Implementation Method 1
a mixing amount of the lithium fluoride is an amount configured to substitute 1 atom or less of oxygen with fluorine
Implementation Method 2
forming a calcined body by subjecting the first mixture to a first heating treatment
Implementation Method 3
performing main firing by subjecting the second mixture to a second heating treatment
Data Source
AI summary
A lithium battery as a secondary battery includes a positive electrode composite material containing a solid electrolyte and a positive electrode active material containing lithium, a negative electrode as an electrode provided at one face of the positive electrode composite material, and a current collector provided at another face of the positive electrode composite material, wherein the solid electrolyte is a garnet-type fluorine-containing lithium composite metal oxide that is represented by the following compositional formula (1) or (2) and that conducts lithium.(Li7−3xGax)(La3−yNdy)Zr2O12−zFz (1)(Li7−3x+yGax)(La3−yCay)Zr2O12−zFz (2)Provided that 0.1≤x≤1.0, 0<y≤0.2, and 0<z≤1.0.