Multi-Cation Doped LLZO Electrolyte for Cubic Phase Stability
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Solution Overview
Problem
Current solid electrolyte materials for Li-ion batteries, such as oxide-based Li-garnet, face limitations in Li-ion conductivity and stability due to the tetragonal crystal structure at room temperature, which is not sufficient for practical applications, and doping methods that improve conductivity often result in decreased Li content and increased costs.
Innovation Solution
The introduction of multiple dopants into the Li7La3Zr2O12 material, specifically a combination of subvalent and supervalent cations for Zr, stabilizes the cubic LLZO phase without inducing Li vacancies, maintaining the overall Li content and achieving higher conductivity and stability through entropic stabilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If substitutional dopants are incorporated to stabilize cubic LLZO phase, then Li-ion conductivity is improved, but Li content decreases due to induced Li vacancies
Solution Approach 1:
The patent changes the doping strategy from inducing Li vacancies to using aliovalent cation doping on Zr sites that maintains charge balance without creating Li vacancies. This parameter change in the doping mechanism allows cubic phase stabilization while preserving Li content.
Solution Approach 2:
The patent applies doping locally at the Zr sites rather than creating vacancies at Li sites. By substituting Zr4+ with aliovalent cations (such as Nb5+, Ta5+, Mo6+) and compensating through oxygen vacancies or mixed valence states, the method stabilizes the cubic phase while maintaining Li content at 7 per formula unit.
2Stability of the object's composition
If Li-site dopants are used to stabilize cubic phase, then cubic structure is stabilized, but Li-ion conductivity decreases due to occupation of Li-ion hopping sites
Solution Approach 1:
The patent applies doping at the Zr sites rather than Li sites. By substituting Zr4+ with aliovalent cations, the method achieves cubic phase stabilization without occupying Li-ion hopping sites, thereby preserving Li-ion conductivity pathways.
Solution Approach 2:
The patent uses Zr site substitution as an intermediary mechanism to stabilize the cubic phase indirectly, rather than directly doping Li sites. This intermediary approach allows phase stabilization while maintaining Li-ion transport channels open.
3Stability of the object's composition
If higher valance elements are used for substitutional doping to induce Li vacancies, then cubic phase is stabilized, but material cost increases
Solution Approach 1:
The patent changes the doping approach to use mixed valence state cations (combining higher valance elements like Nb5+, Ta5+ with lower valance elements or maintaining average valance of 4+). This parameter change allows cubic phase stabilization while using lower amounts of expensive higher-valance elements, reducing material cost.
Solution Approach 2:
The patent employs composite doping strategies combining multiple cation types (e.g., Nb5+ with lower valance cations, or mixed valence states) to achieve cubic phase stabilization. This composite approach distributes the doping burden, reducing reliance on expensive single-element high-valance dopants.
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 Li-ion conductivity, maintains high stability, and reduces material costs by allowing the use of lower-cost elements, while retaining the Li content at 7 per formula unit, effectively stabilizing the cubic phase at room temperature.
Implementation Method 1
stabilizes the cubic LLZO phase without inducing Li vacancies, maintaining the overall Li content and achieving higher conductivity and stability through entropic stabilization
Data Source
AI summary
A lithium garnet material has the formula Li7-δLa3Z2z-x-y-zM1xM2yM3zO12, where M1 is one or a combination of (Y, In, Mg, Ca, Ba, Sc, Sr, Ru) with oxidation number (valence) lower than 4+, M2 is one or a combination of (Bi, Ta, Nb, Mo, Sb, Te) with oxidation number (valence) higher than 4+, and M3 is one or a combination of (Hf, Ti, Sn, Si) with oxidation number (valence) equal to 4+, subject to 0<x≤1, 0≤y≤1, 0≤z≤2, 0<x+y+z≤2, and −0.2<δ<0.2. Also provided is a lithium garnet material which is the same as the aforementioned lithium garnet material except that M1 is one or a combination of (Y, In, Mg, Ca, Ba, Sr, Ru) and M2 is one or a combination of (Bi, Ta, Nb, Mo, Sb, Te, W). Lithium oxide solid-state electrolyte materials have the same formula as the aforementioned lithium garnet materials but also include Ge for M3.