Garnet Solid Electrolyte Composition for Suppressing Electron Leakage
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Solution Overview
Problem
Conventional solid-state batteries using garnet-type solid electrolyte ceramics face issues with increased electron conductivity due to impurity formation, leading to short-circuiting and leakage current, especially when transition metal elements are present in large amounts, which compromises battery performance and density.
Innovation Solution
A solid electrolyte ceramic with a garnet-type crystal structure, comprising lithium, lanthanum, oxygen, and specific transition metal elements like cobalt, nickel, manganese, and iron, is developed, with precise chemical composition and content ratios to suppress electron conductivity while maintaining high ion conductivity and density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Bi is added to garnet-type solid electrolyte to improve ion conductivity, then ion conductivity increases, but Li-Bi-O-based compound impurities form at grain boundaries causing increased electron conductivity and short-circuiting
Solution Approach 1:
A Li-rich glassy phase is introduced as an intermediary layer at the grain boundaries to suppress the formation of conductive Li-Bi-O impurities. This glassy phase acts as a barrier that prevents electron conduction while allowing ion transport, thus resolving the contradiction between maintaining high ion conductivity and preventing harmful electron conductivity increase.
Solution Approach 2:
The composition parameters of the solid electrolyte are optimized by controlling the Bi content within specific ranges (0.1-0.5 mol ratio relative to La) and adjusting the Li content to ensure excess lithium is available for forming the insulating glassy phase at grain boundaries, thereby preventing impurity formation and maintaining low electron conductivity.
2Quantity of substance
If relative density is increased to improve battery capacity, then battery capacity increases, but sintering conditions become more stringent and impurity formation is exacerbated
Solution Approach 1:
The solid electrolyte is designed as a composite material system combining crystalline garnet-phase Li7La3Zr2O12 with amorphous Li-rich glassy phase at grain boundaries. This composite structure achieves high relative density (≥95%) through the sintering behavior of the composite, while the glassy phase simultaneously suppresses impurity formation and provides ion conduction pathways, resolving the contradiction between density and impurity formation.
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 solution effectively reduces electron conductivity, preventing short-circuiting and leakage, while enhancing the relative density and ion conductivity of solid-state batteries, thereby improving their operational reliability and efficiency.
Implementation Method 1
the solid electrolyte layer contains a solid electrolyte ceramic, and is responsible for ion conduction between the positive electrode layer and the negative electrode layer
Data Source
AI summary
A solid electrolyte ceramic that has a garnet-type crystal structure, and contains: at least Li, La, and O; and one or more transition metal elements selected from the group consisting of Co, Ni, Mn, and Fe, wherein, when a content of the Li and a total content of the one or more transition metal elements are denoted respectively by X (mol %) and Y (mol %), the solid electrolyte ceramic satisfies any one of the following relational expressions (1) to (3): (1) 0.01≤Y≤4.00 in the range of 221≤X<227; (2) 0.01≤Y≤6.00 in the range of 227≤X<237; and (3) 0.01≤Y≤8.00 in the range of 237≤X≤250.