Lithium Cell Electrolyte Water Content Optimization
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Solution Overview
Problem
Primary lithium cells with lithium metal anodes and iron disulfide cathodes face challenges in maintaining performance due to the reactivity of lithium with water, leading to passivation layers that can compromise discharge efficiency, and existing electrolytes have limited water content to prevent these issues, which can result in reduced conductivity and cell performance.
Innovation Solution
Incorporating up to 1000 ppm of water into the electrolyte of primary lithium cells with a lithium salt such as Li(CF3SO2)2N dissolved in a solvent mixture of 1,3-dioxolane and sulfolane, which improves electrical conductivity without significantly affecting cell performance, even when used in digital cameras with high power demands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If water content in the electrolyte is limited to prevent lithium reactivity, then cell safety is improved, but electrical conductivity deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the water content in the electrolyte to fall within the range of 10-1000 ppm. This quantitative parameter adjustment resolves the contradiction by finding the optimal water content level that simultaneously ensures cell safety (preventing excessive lithium reactivity) while maintaining adequate electrical conductivity for cell operation.
2Power
If water content in the electrolyte is increased to improve conductivity, then electrical conductivity is improved, but passivation layer formation worsens
Solution Approach 1:
The patent uses parameter changes by establishing a specific water content range (10-1000 ppm) in the electrolyte. This controlled parameter adjustment allows the system to achieve improved electrical conductivity while preventing excessive passivation layer formation that would occur at higher water concentrations.
Solution Approach 2:
The patent applies the blessing in disguise principle by converting the potentially harmful effect of water (which can cause passivation layer formation) into a beneficial effect. By controlling water content within the optimal range, the patent transforms what could be a harmful factor into a means of improving electrical conductivity while maintaining acceptable passivation layer levels.
3Object-generated harmful factors
If water content in the electrolyte is strictly controlled at low levels, then passivation layer formation is reduced, but electrical conductivity deteriorates
Solution Approach 1:
The patent resolves this contradiction through parameter changes by defining an optimal water content range (10-1000 ppm) rather than using strict low-level control. This parameter optimization allows the system to maintain reduced passivation layer formation while simultaneously achieving adequate electrical conductivity, thereby resolving the trade-off between these two factors.
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 increased water content in the electrolyte enhances conductivity, offsetting the adverse effects of passivation layers, resulting in stable and efficient cell performance across various usage conditions, including accelerated storage and discharge tests, without noticeable deterioration in lithium cell performance.
Implementation Method 1
the lithium ions, Li+, produced at the anode must transport through the separator and electrolyte medium and to the cathode
Implementation Method 2
The FeS2 theoretical capacity is based on a 4 electron transfer from 4Li per FeS2 molecule to result in reaction product of elemental iron Fe and 2Li2S
Data Source
AI summary
A primary cell having an anode comprising lithium or lithium alloy and a cathode comprising iron disulfide (FeS2) and carbon particles. The electrolyte comprises a lithium salt dissolved in an organic solvent mixture. The electrolyte contains between about 100 and 2000 parts by weight water per million parts by weight (ppm) electrolyte therein. The electrolyte may contain between about 200 and 2000, or between about 500 and 2000 parts by weight water per million parts by weight electrolyte. A cathode slurry is prepared comprising iron disulfide powder, carbon, binder, and a liquid solvent. The mixture is coated onto a conductive substrate and solvent evaporated leaving a dry cathode coating on the substrate. The anode and cathode can be spirally wound with separator therebetween and inserted into the cell casing with electrolyte then added.