Sulfide Solid Electrolyte with Oxide Coating for Stability
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Solution Overview
Problem
Sulfide solid electrolyte materials in lithium secondary batteries are unstable at high and low potentials, leading to lithium extraction and reduced lithium ion conductivity, which degrades the discharge characteristics of the battery.
Innovation Solution
A sulfide solid electrolyte material with a sulfide layer and an oxide layer, where the oxide layer covers the sulfide layer, with a specific oxygen-to-lithium atom ratio, is used to enhance the stability and conductivity by increasing the proportion of lithium-oxygen bonds, reducing lithium extraction and maintaining ionic conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sulfide solid electrolyte material is used, then high ionic conductivity is achieved, but stability at high and low potentials deteriorates leading to lithium extraction
Solution Approach 1:
The patent applies composite materials by combining sulfide and oxide layers in a core-shell structure. The sulfide layer provides high ionic conductivity while the oxide layer provides stability at high and low potentials, preventing lithium extraction. This composite structure resolves the contradiction between achieving high conductivity and maintaining stability.
Solution Approach 2:
The oxide layer acts as an intermediary protective barrier between the sulfide electrolyte and the electrode materials. It mediates the interaction at the interface, preventing direct contact that would cause lithium extraction, while still allowing lithium ion transport. This intermediary layer resolves the stability-conductivity contradiction.
2Reliability
If the oxide layer thickness is increased to improve stability, then lithium extraction is reduced, but ionic conductivity may deteriorate
Solution Approach 1:
The patent optimizes the oxide layer thickness to a specific range (1-10 nm) to balance stability and conductivity. By precisely controlling this parameter, the oxide layer provides sufficient protection against lithium extraction while maintaining adequate lithium ion transport capability. This parameter optimization resolves the contradiction between stability and conductivity.
Solution Approach 2:
The oxide layer is applied locally as a thin coating on the sulfide particle surface rather than throughout the entire material. This localized application provides protection where needed (at the interface) while minimizing the impact on bulk ionic conductivity. The local quality approach resolves the contradiction between stability and conductivity.
3Reliability
If lithium-oxygen bonds are increased to reduce lithium extraction, then stability is improved, but manufacturing precision is required to control oxygen-to-lithium ratio
Solution Approach 1:
The oxide layer is formed preliminarily on the sulfide particles before battery assembly through controlled oxidation treatment. This preliminary action establishes the desired oxygen-to-lithium ratio and lithium-oxygen bond structure in advance, ensuring stability without requiring complex real-time control during battery manufacturing. The preliminary action approach reduces manufacturing precision requirements.
Data Source
AI summary
A solid electrolyte material includes: a sulfide layer containing lithium atoms and sulfur atoms; and an oxide layer covering the sulfide layer, the oxide layer containing lithium atoms and oxygen atoms. The solid electrolyte material satisfies 0.51≤x and x/y≥1.53, where x is a first ratio of the number of the oxygen atoms to the number of the lithium atoms at a depth 4 nm of the solid electrolyte material from the surface of the oxide layer; and y is a second ratio of the number of the oxygen atoms to the number of the lithium atoms at a depth 100 nm of the solid electrolyte material from the surface of the oxide layer.