Sulfide Solid Electrolyte Phosphorus Site Ratio Control
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Solution Overview
Problem
Sulfide-based solid electrolytes face a limitation in achieving high lithium ion conductivity due to the collapse of their crystal structure when heat treatment temperature is increased, leading to a decrease in crystallinity and conductivity.
Innovation Solution
A sulfide-based solid electrolyte with a LGPS-type crystal structure, comprising lithium, phosphorus, sulfur, and a halogen element, where the ratio of phosphorus atoms occupying 4d and 2b sites in the crystal structure is controlled between 1.77 and 2.14, enhancing lithium ion conductivity without excessive crystallinity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If heat treatment temperature is increased to increase crystallinity, then crystallinity increases, but lithium ion conductivity decreases due to crystal structure collapse
Solution Approach 1:
The invention changes the compositional parameters by introducing a halogen element (X = Cl, Br, or I) into the Li-Li2S-P2S5 system. This compositional modification allows the crystal structure to maintain stability at higher crystallinity levels without collapsing, thereby resolving the contradiction between increasing crystallinity and maintaining lithium ion conductivity. The halogen element acts as a structural modifier that stabilizes the LGPS-type crystal framework.
Solution Approach 2:
The invention creates a composite sulfide-based solid electrolyte material combining Li, Li2S, P2S5, and a halogen element in specific proportions. This composite material approach allows the system to achieve both high crystallinity (70-85%) and high lithium ion conductivity (>2.0 mS/cm) by leveraging the synergistic effects of the multi-component system, where the halogen element reinforces the crystal structure while the sulfide matrix provides ion conduction pathways.
2Stability of the object's composition
If heat treatment time is extended to improve crystallinity, then crystallinity increases, but production time increases and lithium ion conductivity may decrease
Solution Approach 1:
The invention modifies the thermal processing parameters by implementing a two-stage heating process: first heating to 180-250°C for 1-24 hours to form the base crystal structure, then heating to 200-300°C for 0.5-10 hours to achieve final crystallinity optimization. This parameter optimization allows reaching 70-85% crystallinity within 1-34 hours, significantly reducing the traditional 24-240 hour treatment time while maintaining high lithium ion conductivity.
3Stability of the object's composition
If crystallinity is increased beyond optimal level, then crystal structure collapses and diploid phase appears, but lithium ion conductivity decreases
Solution Approach 1:
The invention precisely controls the crystallinity parameter within the 70-85% range through optimized heat treatment parameters (temperature and time) and compositional ratios. This controlled crystallinity level prevents the collapse of the LGPS-type crystal structure and avoids the formation of harmful diploid phases, while still achieving high lithium ion conductivity greater than 2.0 mS/cm. The halogen element content (0.1-5 mol%) also plays a critical role in stabilizing the crystal structure at this optimal crystallinity range.
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 controlled ratio of phosphorus sites in the LGPS-type crystal structure increases lithium ion conductivity while maintaining sufficient crystallinity, preventing the collapse of the crystal structure and enhancing the performance of the sulfide-based solid electrolyte.
Implementation Method 1
it has a LGPS-type crystal structure, and wherein a ratio (P4d/P2b) between a proportion (P4d) of an area of a peak assigned to phosphorus atoms occupying 4d sites in the crystal structure and a proportion (P2b) of an area of a peak assigned to phosphorus atoms occupying 2b sites
Implementation Method 2
When, in the production of a sulfide-based solid electrolyte, a heat treatment temperature is increased for the purpose of increasing the crystallinity of the sulfide-based solid electrolyte
Implementation Method 3
both of which are peaks observed in a 31P-MAS-NMR spectrum of the sulfide-based solid electrolyte
Data Source
AI summary
Provided is a sulfide-based solid electrolyte with high lithium ion conductivity. The sulfide-based solid electrolyte may be a sulfide-based solid electrolyte, wherein the sulfide-based solid electrolyte comprises a lithium (Li) element, a phosphorus (P) element, a sulfur (S) element and a halogen element, and it has a LGPS-type crystal structure, and wherein a ratio (P4d/P2b) between a proportion (P4d) of an area of a peak assigned to phosphorus atoms occupying 4d sites in the crystal structure and a proportion (P2b) of an area of a peak assigned to phosphorus atoms occupying 2b sites in the crystal structure, both of which are peaks observed in a 31P-MAS-NMR spectrum of the sulfide-based solid electrolyte, is 1.77 or more and 2.14 or less.