Aqueous Lithium Sulfur Battery Electrolyte for Cycle Life
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Solution Overview
Problem
Lithium sulfur batteries face challenges in commercialization due to issues with sulfur electrode performance, particularly in maintaining electrochemical reversibility and cycle life, especially at high area capacities.
Innovation Solution
The development of novel aqueous lithium sulfur battery cells using a lithium anode, a solid electron transfer medium cathode, and an aqueous electrolyte with electroactive sulfur species, where the electrolyte includes a cycle-life enhancing compound that extends the stoichiometric solubility limit and facilitates electrochemical oxidation kinetics, allowing for improved cathode reversibility and extended cycle life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional sulfur electrodes are used in lithium sulfur batteries, then high theoretical capacity (1675 mAhg−1) and specific energy (2300 Wh/kg) are achieved, but electrochemical reversibility and cycle life deteriorate
Solution Approach 1:
Aqueous electrolyte containing cycle-life enhancing compounds serves as an intermediary between the sulfur cathode and lithium anode, facilitating reversible electrochemical reactions while preventing direct harmful interactions. The electrolyte mediates ion transport and stabilizes sulfur species during cycling.
Solution Approach 2:
The patent modifies the electrolyte composition by introducing cycle-life enhancing compounds and adjusting stoichiometric ratios of sulfur to lithium species. These parameter changes in electrolyte chemistry enable improved reversibility and extended cycle life while maintaining high capacity.
2Quantity of substance
If high area capacities are used in sulfur cathodes, then energy density is improved, but precipitation of elemental sulfur occurs and reversibility deteriorates
Solution Approach 1:
The patent adjusts electrolyte composition parameters including cycle-life enhancing compound concentrations and stoichiometric ratios to prevent sulfur precipitation even at high area capacities. The modified electrolyte parameters maintain sulfur species in solution during high-capacity cycling.
Solution Approach 2:
The cycle-life enhancing compounds are pre-added to the electrolyte to cushion against the harmful effects of sulfur precipitation before it occurs. This preventive approach allows the system to tolerate high area capacities without losing reversibility.
3Ease of manufacture
If aqueous electrolyte is used instead of conventional non-aqueous electrolyte, then safety and cost are improved, but electrochemical window and conductivity are limited
Solution Approach 1:
The patent modifies aqueous electrolyte parameters by adding cycle-life enhancing compounds and optimizing sulfur-to-lithium stoichiometric ratios. These changes expand the effective electrochemical window and improve conductivity while maintaining the safety and cost advantages of aqueous systems.
Solution Approach 2:
The electrolyte is formulated as a composite system combining water with cycle-life enhancing compounds. This composite approach leverages the safety and cost benefits of water while the added compounds provide enhanced electrochemical performance comparable to non-aqueous systems.
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 solution enhances cycle life and reversibility of lithium sulfur battery cells, enabling more than 100 cycles at high area capacities without precipitation of elemental sulfur, thereby addressing the limitations of existing sulfur electrode technologies.
Implementation Method 1
The aqueous electrolyte facilitates electrochemical oxidation kinetics
Implementation Method 2
an aqueous electrolyte in electron transfer contact with the cathode
Implementation Method 3
the electrolyte includes a cycle-life enhancing compound that extends the stoichiometric solubility limit
Data Source
AI summary
Lithium sulfur battery cells that use water as an electrolyte solvent provide significant cost reductions. Electrolytes for the battery cells may include water solvent for maintaining electroactive sulfur species in solution during cell discharge and a sufficient amount of a cycle life-enhancing compound that facilitates charging at the cathode. The combination of these two components enhances one or more of the following cell attributes: energy density, power density and cycle life. For instance, in applications where cost per Watt-Hour (Wh) is paramount, such as grid storage and traction applications, the use of an aqueous electrolyte in combination with inexpensive sulfur as the cathode active material can be a key enabler for the utility and automotive industries, for example, providing a cost effective and compact solution for load leveling, electric vehicles and renewable energy storage. Sulfur cathodes, and methods of fabricating lithium sulfur cells, in particular for loading lithium sulfide into the cathode structures, provide further advantages.