Lithium-Sulphur Cell Dinitrile Electrolyte Assembly
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithium-sulphur cells face challenges in achieving high gravimetric energy, cycle life, and ease of assembly due to the complex solvent requirements introduced by intermediate species formed during charge and discharge, with many solvents reacting with polysulphides at high sulphur loadings, making it difficult to predict performance from lithium-ion cell solvents.
Innovation Solution
The use of dinitrile-based electrolytes with specific chemical structures, such as 2-methylglutaronitrile, as solvents in lithium-sulphur cells, which enhance gravimetric energy, cycle life, and low-temperature performance by maintaining liquid form at sub-zero temperatures and facilitating efficient cell assembly with favorable viscosity characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional solvents (carbonates) are used in lithium-sulphur cells, then the cell can be assembled using standard procedures, but the solvents react with polysulphides at high sulphur loadings, reducing cycle life and performance
Solution Approach 1:
The patent changes the chemical composition parameter of the electrolyte solvent from conventional carbonates to a specific cyclic carbonate (EC, EMC, or EDC) combined with a chain nitrile (acetonitrile, propionitrile, or butyronitrile). This parameter change resolves the contradiction by selecting solvents that do not react with polysulphides, thereby maintaining both ease of assembly and improved cycle life.
Solution Approach 2:
The patent employs a composite electrolyte system combining a cyclic carbonate and a chain nitrile in specific ratios (60:40 to 90:10). This composite approach leverages the beneficial properties of both solvent types: the cyclic carbonate provides good ionic conductivity and the chain nitrile provides excellent polysulphide solubility, resolving the contradiction between ease of manufacture and reliability.
2Quantity of substance
If the electrolyte solvent must dissolve polysulphide species, then good solvent properties are achieved, but many solvents react with polysulphides particularly at high sulphur loadings
Solution Approach 1:
The patent changes the solvent type parameter from conventional carbonates to a specific combination of cyclic carbonate and chain nitrile. The chain nitrile component (acetonitrile, propionitrile, or butyronitrile) provides excellent solubility for polysulphide species without reacting with them, even at high sulphur loadings, thereby resolving the contradiction between solubility and harmful reactions.
3Use of energy by moving object
If high sulphur loading is used to increase gravimetric energy, then energy density improves, but solvent reactions with polysulphides worsen
Solution Approach 1:
The patent changes the electrolyte composition parameter to use a cyclic carbonate combined with a chain nitrile in specific ratios. This parameter change enables the system to tolerate high sulphur loadings (up to 70-80 wt% of cathode mass) without harmful solvent-polysulphide reactions, thereby achieving high gravimetric energy while avoiding the worsening effect.
4Adaptability or versatility
If lithium-sulphur cell is designed for rechargeability, then secondary cell functionality is achieved, but complex solvent requirements are introduced due to intermediate species
Solution Approach 1:
The patent employs a universal electrolyte system combining cyclic carbonate and chain nitrile that performs multiple functions: it dissolves polysulphide intermediates, maintains ionic conductivity, prevents harmful reactions, and supports reversible charge-discharge cycles. This multi-functional electrolyte composition simplifies the overall system complexity while enabling rechargeability.
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 dinitrile-based electrolytes increase gravimetric energy density, improve cycle life, and enhance low-temperature performance of lithium-sulphur cells, while allowing for convenient cell assembly, as demonstrated by improved charge-discharge curves and energy densities compared to reference cells using sulfolane or mononitrile solvents.
Implementation Method 1
a liquid electrolyte comprising at least one lithium salt and a solvent comprising a dinitrile
Implementation Method 2
Electrolyte is introduced into the cell to wet the cathode and separator
Implementation Method 3
When a lithium-sulphur cell is discharged, the sulphur in the cathode is reduced in two-stages. In the first stage, the electroactive sulphur material (e.g. elemental sulphur) is reduced to polysulphide species, Sn2− (n≥2)
Implementation Method 4
When the cell is charged, the two-stage mechanism occurs in reverse, with the lithium sulphide being oxidised to lithium polysulphide and thereafter to lithium and sulphur
Data Source
AI summary
The present invention relates to a lithium-sulphur cell comprising an anode comprising lithium metal or lithium metal alloy;a cathode comprising a mixture of electroactive sulphur material and solid electroconductive material; and a liquid electrolyte comprising at least one lithium salt and a solvent comprising a dinitrile.