Gallium-Doped LLZO Solid Electrolyte Sintering
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Solution Overview
Problem
Conventional lithium secondary batteries with liquid electrolytes pose safety risks due to flammability, and solid electrolytes like LLZO face challenges with sinterability and variable ionic conductivity depending on crystal structure, making it difficult to achieve high ionic conductivity and practical application.
Innovation Solution
A gallium-doped lithium lanthanum zirconium oxide (LLZO) solid electrolyte is developed by adjusting the ratio of gallium and lithium elements in the starting material, processed through coprecipitation, washing, drying, mixing with a lithium source, and calcination to achieve a cubic crystal structure with enhanced ionic conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LLZO solid electrolyte is used to achieve high ionic conductivity, then ionic conductivity is improved, but sinterability deteriorates and processing becomes difficult
Solution Approach 1:
Gallium oxide (Ga2O3) is introduced as an intermediary substance to facilitate the sintering process. The Ga2O3 acts as a sintering aid that promotes grain growth and densification of LLZO particles during sintering, thereby improving sinterability while maintaining the high ionic conductivity of the base LLZO material.
Solution Approach 2:
The chemical composition parameters of the solid electrolyte are modified by adding gallium oxide at specific concentrations (0.1-0.5 mole%). This parameter change alters the sintering behavior and crystal structure of LLZO, enabling better sinterability while preserving the desired ionic conductivity properties.
2Reliability
If LLZO solid electrolyte is used to achieve high ionic conductivity, then ionic conductivity is improved, but processing complexity increases due to lithium volatilization
Solution Approach 1:
Gallium oxide serves as a protective intermediary during the sintering process, reducing lithium volatilization by forming a stable chemical environment that suppresses lithium loss. This simplifies processing by eliminating the need for complex lithium replenishment procedures.
Solution Approach 2:
The problematic aspect of lithium volatilization is extracted and addressed separately through the addition of gallium oxide, which specifically targets and mitigates the lithium loss issue without affecting other processing aspects, thereby reducing overall processing complexity.
3Reliability
If gallium doping is increased to improve ionic conductivity, then ionic conductivity increases, but crystal structure control becomes more difficult
Solution Approach 1:
The gallium content is optimized within a specific range (0.1-0.5 mole%) to achieve the desired balance between ionic conductivity enhancement and crystal structure stability. This parameter optimization ensures that the cubic garnet structure is maintained while achieving improved ionic conductivity.
Solution Approach 2:
The solid electrolyte is designed as a composite system combining LLZO with controlled amounts of gallium oxide. This composite approach allows the benefits of gallium doping (enhanced ionic conductivity) while the overall composition is engineered to maintain structural stability and control over the crystal phase.
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 gallium-doped LLZO solid electrolyte exhibits increased ionic conductivity and improved sinterability, achieving higher performance and stability, as demonstrated by measurements of impedance and potential window testing, making it suitable for all-solid-state lithium secondary batteries.
Implementation Method 1
a lithium lanthanum zirconium oxide (LLZO) is doped with a gallium element (Ga)... the ratio of a gallium element in a starting material and a lithium element from a lithium source is adjusted to thus control the crystal structure
Implementation Method 2
preparing a solid electrolyte precursor by subjecting a mixed solution comprising a lanthanum precursor, a zirconium precursor, a gallium precursor, a complexing agent, and a pH adjuster to coprecipitation
Implementation Method 3
calcining the mixture to give a calcined solid electrolyte, which is a gallium (Ga)-doped lithium lanthanum zirconium oxide (LLZO)
Implementation Method 4
a method of preparing a sintered solid electrolyte... controlling sintering properties
Data Source
AI summary
A method of preparing a sintered solid electrolyte includes (a) coprecipitating a mixed solution including a lanthanum precursor, a zirconium precursor, a gallium precursor, a complexing agent, and a pH adjuster to provide a solid electrolyte precursor; (b) washing and drying the solid electrolyte precursor to provide a washed and dried solid electrolyte precursor; (c) mixing the washed and dried solid electrolyte precursor with a lithium source to provide a mixture; (d) calcining the mixture to provide a calcined solid electrolyte, which is a gallium (Ga)-doped lithium lanthanum zirconium oxide (LLZO), as represented by Chemical Formula 1 below,LixLayZrzGawO12, Chemical Formula 1where 5≤x≤9, 2≤y≤4, 1≤z≤3, and 0<w≤4; and(e) sintering the calcined solid electrolyte at a temperature ranging from 1,000° C. to 1,300° C. to provide the sintered solid electrolyte,wherein a ratio (M1:M2) of moles (M1) of lithium element to moles (M2) of gallium element ranges from 6.7:0.1 to 5.8:0.4.