Sulfide Solid Electrolyte Crystallinity Control via LiBr
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Solution Overview
Problem
The challenge is to enhance Li ion conductivity in sulfide solid electrolyte materials without generating a low Li ion conducting phase, as increasing heat treatment temperature or time to achieve higher crystallinity of the high Li ion conducting phase is difficult and often results in the formation of a low Li ion conducting phase, limiting the overall conductivity.
Innovation Solution
A sulfide solid electrolyte material with specific composition and heat treatment conditions is developed, characterized by peaks at 2θ=20.2° and 23.6° in X-ray diffraction, and a differential thermal analysis exothermic peak difference of ≥55°C, which allows for increased crystallinity of the high Li ion conducting phase without generating the low Li ion conducting phase, using a composition of Li, P, I, and S with LiBr/(LiI+LiBr) in the range of 25 mol % to 50 mol % and Li2S/(Li2S+P2S5) in the range of 76 mol % to 78 mol %.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat treatment temperature or time is increased to improve crystallinity of high Li ion conducting phase, then Li ion conductivity is improved, but a low Li ion conducting phase is generated which reduces overall conductivity
Solution Approach 1:
The invention changes the chemical composition parameters of the sulfide solid electrolyte material by introducing specific ratios of LiI and LiBr (where LiBr/(LiI+LiBr) is 25-50 mol%). This compositional modification shifts the exothermic peak temperature in differential thermal analysis to a higher temperature range, allowing crystallization to occur at temperatures that favor the high Li ion conducting phase while suppressing the formation of the low Li ion conducting phase.
Solution Approach 2:
LiBr acts as an intermediary substance that modifies the crystallization behavior of the system. By adding LiBr to the Li2S-P2S5-LiI system, the invention creates a compositional buffer that raises the exothermic peak temperature, thereby mediating between the desire for high crystallinity and the need to avoid low-conductivity phases.
2Stability of the object's composition
If heat treatment is carried out at conditions that prevent low Li ion conducting phase formation, then phase stability is maintained, but crystallinity of high Li ion conducting phase cannot be increased
Solution Approach 1:
The invention modifies the thermal analysis parameters by changing the chemical composition to include specific LiI-LiBr ratios. This compositional change shifts the exothermic peak to a higher temperature, creating a thermal window where both high crystallinity and phase stability can be achieved simultaneously. The modified composition allows heat treatment at temperatures that ensure complete crystallization without triggering unwanted phase formation.
3Reliability
If LiI is added to Li2S-P2S5-based sulfide solid electrolyte to improve Li ion conductivity, then conductivity increases, but the exothermic peak temperature decreases making phase control difficult
Solution Approach 1:
LiBr serves as a counteracting substance that offsets the temperature-lowering effect of LiI addition. While LiI increases Li ion conductivity, it also decreases the exothermic peak temperature. The addition of LiBr counterbalances this effect by raising the exothermic peak temperature back to a favorable range, allowing both high conductivity and stable phase formation to coexist.
Solution Approach 2:
The invention creates a composite sulfide solid electrolyte system combining Li2S, P2S5, LiI, and LiBr in specific ratios. This composite material approach allows the synergistic effects of multiple components: LiI provides high Li ion conductivity while LiBr stabilizes the thermal behavior, and P2S5 forms the glass matrix. The composite structure enables simultaneous achievement of high conductivity and stable phase composition.
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 results in a sulfide solid electrolyte material with high Li ion conductivity, suitable for high-output solid state lithium batteries, as it maintains high crystallinity of the high Li ion conducting phase while suppressing the formation of the low Li ion conducting phase, thereby enhancing battery performance.
Implementation Method 1
a sulfide solid electrolyte material having a high Li ion conductivity
Implementation Method 2
peaks at 2θ=20.2° and 23.6° in an X-ray diffraction measurement using a CuKα ray
Implementation Method 3
peaks at 2θ=20.2° and 23.6° in an X-ray diffraction measurement
Implementation Method 4
when the heat treatment temperature is increased or heat treatment time is extended in order to have higher crystallinity
Implementation Method 5
the crystallinity of a high Li ion conducting phase can be increased
Implementation Method 6
a tiny exothermic peak present at higher temperature side than the exothermic peak of a high Li ion conducting phase in differential thermal analysis
Data Source
AI summary
A sulfide solid electrolyte material having a high Li ion conductivity is provided. A sulfide solid electrolyte material includes Li, P, I and S, having peaks at 2θ=20.2° and 23.6°, not having peaks at 2θ=21.0° and 28.0° in an X-ray diffraction measurement using a CuKα ray, and having a half width of the peak at 2θ=20.2° of 0.51° or less.