Garnet Electrolyte Grain Boundary Resistance
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Solution Overview
Problem
Existing all-solid batteries face challenges with insufficient sintering at the interface between crystal grains, leading to high grain boundary resistance and poor lithium ion conductivity, especially when using low-temperature firing methods for garnet-type ion conductive oxides.
Innovation Solution
The use of a lithium composite oxide electrolyte with gallium substituting the lithium site and calcium substituting the lanthanum site in lithium lanthanum zirconate, as represented by the formula (Li7−3x+yGax)(La3−yCay)Zr2O12, reduces grain boundary resistance and improves lithium ion conductivity by minimizing particle size and increasing the contact area between particles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If low-temperature firing is used for garnet-type ion conductive oxide, then energy consumption is reduced and manufacturing cost decreases, but sintering at the interface between crystal grains becomes insufficient leading to high grain boundary resistance
Solution Approach 1:
The patent modifies the chemical composition parameters of the garnet-type electrolyte by introducing aluminum substitution at the zirconium site and controlling the ratios of lithium, lanthanum, and zirconium. This compositional parameter change enables sufficient sintering and reduced grain boundary resistance at lower firing temperatures (900-1000°C), resolving the contradiction between energy consumption and grain boundary resistance.
Solution Approach 2:
The patent creates a composite electrolyte material by substituting aluminum into the zirconium site of the garnet structure, forming a multi-element composite (Li-La-Zr-Al-O system). This composite material achieves both low-temperature processability and low grain boundary resistance through the synergistic effect of multiple elements, resolving the contradiction between firing temperature and sintering quality.
2Reliability
If high temperature firing is used to reduce grain boundary resistance, then lithium ion conductivity improves, but composition change occurs as lithium is abstracted from electrolyte particles
Solution Approach 1:
The patent optimizes the compositional parameters by introducing aluminum substitution and controlling the stoichiometric ratios in the Li7-xAlxLa3Zr2-yAlzO12 system. This parameter optimization stabilizes the electrolyte composition during firing, preventing lithium abstraction while maintaining high lithium ion conductivity through controlled sintering at 900-1000°C.
Solution Approach 2:
Aluminum acts as an intermediary element that stabilizes the garnet structure during firing. The aluminum substitution at the zirconium site reinforces the crystal structure, preventing lithium loss while enabling sufficient sintering. This intermediary element mediates between the conflicting requirements of high temperature sintering and composition stability.
3Shape
If gallium substitutes the lithium site in lithium lanthanum zirconate, then particle size increases producing coarse particles, but lithium ion conductivity decreases due to smaller contact area between particles
Solution Approach 1:
The patent changes the substitution element from gallium to aluminum and optimizes the substitution ratio (z value in Li7-xAlxLa3Zr2-yAlzO12). Aluminum substitution produces finer particles compared to gallium, increasing the contact area between particles while maintaining structural stability. This parameter change resolves the contradiction between particle size and lithium ion conductivity.
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 configuration results in a battery with reduced grain boundary resistance and enhanced lithium ion conductivity, even when using low-purity lithium compounds, leading to improved battery performance and capacity.
Implementation Method 1
substituting the lithium site with gallium in lithium lanthanum zirconate tends to produce coarse particles. Increased numbers of coarse particles make the contact area between particles smaller, and lead to poor lithium ion conductivity (total ion conductivity). Such generation of coarse particles can be reduced, and the particle size can be made smaller by further substituting the lanthanum site with calcium.
Implementation Method 2
the contact area between particles increases upon forming an electrolyte layer from the electrolyte by compression molding. These small electrolyte particles become densely packed to form the electrolyte layer, and reduce the grain boundary resistance.
Data Source
AI summary
A electrolyte is an electrolyte represented by the following formula (1):(Li7−3x+yGax)(La3−yCay)Zr2O12 (1)wherein 0.1≤x≤1, and 0.01≤y≤0.5.