Non-aqueous Redox Flow Battery with Cation-Permeable Separator
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Solution Overview
Problem
Current redox flow batteries based on aqueous electrochemistry are limited by the electrochemical properties of water, leading to low energy densities, low round-trip efficiencies, and high costs, while non-aqueous systems face challenges with low efficiencies and limited solubility of coordination complexes.
Innovation Solution
A non-aqueous redox flow battery design featuring a negative electrode and a positive electrode immersed in separate liquid electrolytes, with a cation-permeable separator allowing cations to shuttle between them, utilizing transition metal-free redox reactants and electrolyte salts like alkali metal salts to balance charges during charging and discharging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aqueous electrochemistry is used in redox flow batteries, then the system is stable and safe, but energy density and round-trip efficiency are limited due to water's narrow electrochemical stability window
Solution Approach 1:
The patent changes the fundamental parameter of the electrolyte from aqueous to non-aqueous (organic), which expands the electrochemical stability window from ~1.6V to >3V. This parameter change enables higher cell potentials and significantly higher energy densities while maintaining system functionality through careful selection of organic solvents and redox-active compounds.
Solution Approach 2:
The patent employs composite electrolyte systems combining organic solvents with redox-active compounds (such as quinone derivatives, viologens, or metal-free organic molecules) to create a functional non-aqueous electrolyte that provides both the expanded voltage window and the necessary electrochemical activity for high energy density storage.
2Quantity of substance
If non-aqueous electrolytes are used to expand electrochemical stability window, then energy density and cell potential increase, but system complexity and cost increase due to specialized materials requirements
Solution Approach 1:
The patent employs inexpensive, commercially available organic compounds (such as quinone derivatives, viologens, or other organic redox mediators) that can be synthesized through simple, scalable processes. These materials replace expensive coordination complexes while providing sufficient stability and performance, effectively using 'cheap' materials to achieve high energy density without proportionally increasing system complexity.
3Power
If coordination complexes are used in non-aqueous systems, then cell potential increases, but solubility is limited and efficiencies decrease
Solution Approach 1:
The patent extracts the metal center from the coordination complex, transitioning from metal-based redox couples to metal-free organic redox molecules. This extraction eliminates the solubility limitations inherent to coordination complexes while maintaining high cell potentials through carefully designed organic molecules with appropriate redox potentials and enhanced solubility characteristics.
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
This design enhances energy and power densities, increases system reliability, and reduces hardware costs by operating at higher cell potentials, while tailoring performance through selection of redox reactants and electrolyte compositions.
Implementation Method 1
a cation-permeable separator (e.g., a membrane or other cation-permeable material) partitioning the negative electrode/anolyte from the positive electrode/catholyte. During charging and discharging, the electrolytes are circulated over their respective electrodes, while cations shuttle between the two electrolytes to balance the charges
Implementation Method 2
redox flow batteries, which are rechargeable electrochemical energy storage devices that utilize the oxidation and reduction of two soluble electroactive species for charging (absorbing energy) and discharging (delivering energy)
Data Source
AI summary
The present invention provides a non-aqueous redox flow battery comprising a negative electrode immersed in a non-aqueous liquid negative electrolyte, a positive electrode immersed in a non-aqueous liquid positive electrolyte, and a cation-permeable separator (e.g., a porous membrane, film, sheet, or panel) between the negative electrolyte from the positive electrolyte. During charging and discharging, the electrolytes are circulated over their respective electrodes. The electrolytes each comprise an electrolyte salt (e.g., a lithium or sodium salt), a transition-metal free redox reactant, and optionally an electrochemically stable organic solvent. Each redox reactant is selected from an organic compound comprising a conjugated unsaturated moiety, a boron cluster compound, and a combination thereof. The organic redox reactant of the positive electrolyte is selected to have a higher redox potential than the redox reactant of the negative electrolyte.