LLZO Ceramic Two-Step Sintering for Dense Uniform Grain Structure
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Solution Overview
Problem
Conventional lithium-ion batteries using liquid electrolytes face safety risks such as leakage and explosion, while all-solid-state batteries with solid electrolytes like garnet-structured lithium lanthanum zirconium oxide (LLZO) ceramic offer improved safety but struggle with abnormal grain growth (AGG) during sintering, affecting densification and manufacturing complexity.
Innovation Solution
A two-step sintering process is employed, with different temperatures and durations for the first and second sintering operations, along with doping of LLZO powder particles, to produce a dense LLZO-based ceramic with controlled grain size and suppressed AGG, achieving a relative density of 88% or greater and grain sizes ranging from 1 to 10 µm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If a single high-temperature sintering operation is performed to achieve high density, then densification is improved, but abnormal grain growth occurs
Solution Approach 1:
The sintering process is divided into two distinct stages: a first sintering operation at high temperature (1000-1400°C) for short duration to achieve rapid densification, followed by a second sintering operation at lower temperature (900-1200°C) for longer duration to control grain growth. This segmentation allows independent optimization of density and grain size control that cannot be achieved in a single sintering step.
2Volume of stationary object
If sintering temperature is increased to improve densification, then density is improved, but grain boundary resistance increases
Solution Approach 1:
The sintering process employs dynamic temperature adjustment, transitioning from high temperature to lower temperature between two operations. This dynamic approach allows the material to achieve high density at elevated temperature while subsequent cooling and lower-temperature treatment maintains fine grain structure and low grain boundary resistance, optimizing both densification and ionic conductivity.
3Volume of stationary object
If sintering time is extended to improve density, then densification is improved, but abnormal grain growth occurs
Solution Approach 1:
The sintering process uses periodic action with two distinct time-temperature cycles: a first cycle at high temperature for short time to achieve rapid densification, followed by a second cycle at lower temperature for extended time to control grain growth. This periodic approach prevents continuous high-temperature exposure that causes abnormal grain growth while maintaining high density.
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 results in a dense LLZO-based ceramic with controlled grain growth, enhancing the safety and energy density of all-solid-state lithium secondary batteries by inhibiting abnormal grain growth and improving sinterability.
Implementation Method 1
a sintering operation of sintering an oxide sheet including LLZO powder particles
Implementation Method 2
a first sintering operation of sintering at a temperature of T1; and a second sintering operation of sintering at a temperature of T2, lower than T1
Data Source
Figure 1(a)~2(b)
Figure 3(a)~4(b)
Figure 5(a)~6(b)
AI summary
A method for producing a lithium lanthanum zirconium oxide (LLZO)-based ceramic according to an embodiment of the present invention comprises a sintering operation of sintering an oxide sheet that includes LLZO powder particles including the elements lithium, lanthanum, and zirconium. The sintering operation may include a first sintering operation of sintering at a temperature of T1 and a second sintering operation of sintering at a temperature of T2 lower than T1. An LLZO-based ceramic according to another embodiment of the present invention has a relative density of at least 88% and is composed of grains having a size of 1-10 µm, wherein the standard deviation of the grain size is 80% or less of the average grain size, and the grains may have a cubic crystal structure.