Al-Doped LiTi2(PS4)3 Solid Electrolyte Conductivity
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Solution Overview
Problem
The existing methods for preparing lithium titanium thiophosphate LiTi2(PS4)3 do not optimize ionic conductivity, which is crucial for high-energy density all-solid-state battery systems.
Innovation Solution
A compound represented by the formula Li1+xAlxTi2−x(PS4)3 is synthesized through a method involving mechanical milling or melt-quenching of lithium sulfide, phosphorus sulfide, aluminum sulfide, and titanium sulfide, followed by heat treatment at temperatures between 350°C and 500°C, optimizing the ionic conductivity by aliovalent substitution of Ti with Al.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Al doping is increased to improve ionic conductivity, then ionic conductivity increases up to x=0.5, but conductivity decreases above x=0.5 due to strong Li-Li interactions
Solution Approach 1:
The patent applies parameter changes by systematically varying the Al doping concentration (x value) to optimize ionic conductivity. The composition parameter x is tuned within the range 0.1≤x≤0.75, with optimal performance at x=0.5, demonstrating how changing compositional parameters can maximize ionic conductivity while managing Li-Li interaction effects.
Solution Approach 2:
The patent creates a composite material system by doping Al into the LiTi2(PS4)3 structure to form Li1+xAlxTi2−x(PS4)3. This composite approach combines the base lithium titanium thiophosphate with aluminum dopant atoms, leveraging the synergistic effects to enhance ionic conductivity while maintaining structural integrity.
2Manufacturing precision
If heat treatment temperature is increased to improve crystallization, then material formation improves, but excessive temperature may cause unwanted phase formation or degradation
Solution Approach 1:
The patent applies parameter changes by optimizing the heat treatment temperature parameter within a specific range (350-500°C). This controlled temperature parameter ensures adequate crystallization for material formation while preventing the formation of unwanted phases that could occur at excessive temperatures.
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 method achieves high ionic conductivity within the range of 0.1≤x≤0.75, particularly 0.3≤x≤0.6, enhancing the material's performance as a solid electrolyte without altering the crystal structure, but conductivity decreases above x=0.5 due to strong Li—Li interactions.
Implementation Method 1
Ti is substituted aliovalently by Al (Ti4+→Li++Al3+), which appears to result in an increase in the number of Li without changing the crystal structure, and therefore in an increased ionic conductivity.
Implementation Method 2
subjecting the mixture prepared in (b) to a heat treatment step at a maximum plateau temperature of at least 350° C. and less than 500° C.
Implementation Method 3
subjecting the mixture prepared in step (a) to a preliminary reaction step through mechanical milling or melt-quenching to produce an intermediate amorphous sulfide mixture
Data Source
AI summary
A compound represented by the general formula Li1+xAlxTi2−x(PS4)3, wherein 0.1≤x≤0.75. The above compound has been found to have high ionic conductivity. Also, the use of the compound as a solid electrolyte, in particular in an all solid-state lithium battery.