Low-Crystalline Vanadium Sulfide Cathode With Phosphorus for Cycle Stability
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Solution Overview
Problem
Current lithium-ion secondary batteries face challenges with low initial capacity and deteriorating coulombic efficiency in charge-and-discharge cycles, particularly in mid-term cycles, due to the limitations of crystalline vanadium sulfides.
Innovation Solution
A phosphorus-containing low-crystalline vanadium sulfide with specific composition ratios of P/V and S/V, having a VS4-type crystal structure and characteristic X-ray diffraction peaks, is produced through mechanical milling to enhance initial capacity and improve charge-and-discharge cycle characteristics and coulombic efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If crystalline vanadium sulfide is used as cathode active material, then electronic conductivity is improved, but capacity is limited by crystal space groups and dissolution into organic electrolyte occurs
Solution Approach 1:
The patent changes the crystalline structure parameter to low-crystalline state, which disrupts the rigid crystal space group limitations while maintaining sufficient electronic conductivity through the vanadium sulfide framework. This allows Li insertion/extraction at multiple sites beyond what crystalline structures permit.
Solution Approach 2:
The patent creates a composite system combining low-crystalline vanadium sulfide with sulfur, where the vanadium sulfide provides electronic conductivity and structural stability while sulfur provides high capacity. The low-crystalline state reduces dissolution into organic electrolyte compared to pure sulfur.
2Quantity of substance
If sulfur content in metal sulfides is increased to exceed maximum capacity, then capacity is improved, but dissolution into organic electrolyte and structural change during charging-discharging worsen
Solution Approach 1:
The low-crystalline vanadium sulfide acts as an intermediary material between pure sulfur and crystalline metal sulfides. It provides a framework that limits sulfur dissolution into organic electrolyte while allowing high sulfur content for capacity. The vanadium sulfide network stabilizes the structure during charging-discharging cycles.
3Quantity of substance
If low-crystalline vanadium sulfide is used to improve initial capacity, then initial capacity is improved, but coulombic efficiency deteriorates in mid-term charge-and-discharge cycles
Solution Approach 1:
The patent optimizes the composition parameters of vanadium, phosphorus, and sulfur to achieve a balance between initial capacity and mid-term coulombic efficiency. The specific P/V ratio of 0.1 to 1.0 modifies the low-crystalline structure to improve structural stability during cycling while maintaining high initial capacity.
4Reliability
If phosphorus content is increased to improve mid-term coulombic efficiency, then coulombic efficiency is improved, but initial capacity may be affected
Solution Approach 1:
The patent identifies an optimal parameter range for phosphorus content (P/V ratio of 0.1 to 1.0) that simultaneously improves mid-term coulombic efficiency while maintaining high initial capacity. This parameter optimization balances the competing requirements of structural stability and capacity.
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 phosphorus-containing low-crystalline vanadium sulfide achieves a sufficiently high initial capacity and maintains improved coulombic efficiency in mid-term charge-and-discharge cycles, reducing the risk of sulfur dissolution and solvent reactions.
Implementation Method 1
a phosphorus-containing low-crystalline vanadium sulfide... is produced through mechanical milling
Implementation Method 2
sites of crystalline metal sulfides into which Li can be inserted during discharging are defined by crystal space groups... a specific low-crystalline vanadium sulfide allows an improvement in the actual capacity
Data Source
AI summary
An electrode active material for lithium-ion secondary batteries that has a sufficiently high initial capacity, improved charge-and-discharge cycle characteristics, and improved coulombic efficiency in the mid-term charge-and-discharge cycles can be obtained by a phosphorus-containing low-crystalline vanadium sulfide comprising vanadium, phosphorus, and sulfur as constituent elements, the composition ratio of the phosphorus to the vanadium (P/V) being 0.1 to 1.0 in terms of the molar ratio, the composition ratio of the sulfur to the vanadium (S/V) being 4.00 to 10.00 in terms of the molar ratio.