Size-Exclusion Membrane for Non-Aqueous Redox Flow Batteries
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Non-aqueous redox flow batteries face challenges due to lower power and current density compared to aqueous counterparts, primarily due to crossover of redox active particles through the separating membrane, which affects overall performance and increases costs with expensive ion exchange membranes.
Innovation Solution
The use of a size-exclusion membrane that allows counter ions to pass through while preventing the crossover of redox active polymers and colloidal particles, utilizing viologen-based polymers and colloidal particles with specific molecular weights and sizes to enhance energy density and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If ion exchange membranes are used as separators in non-aqueous redox flow batteries, then ionic conductivity is provided for minimizing losses due to resistance to current flow, but the power density decreases by one order of magnitude compared to aqueous redox flow batteries and the cost increases significantly
Solution Approach 1:
The patent extracts the problematic ion exchange membrane component from the system and replaces it with a size-exclusion membrane. This removal eliminates the source of high resistance while maintaining the essential separation function, thereby resolving the contradiction between minimizing energy losses and maintaining power density.
Solution Approach 2:
The size-exclusion membrane performs multiple functions: it provides physical separation of redox species, enables ionic conductivity through pore transport, and eliminates the need for expensive ion exchange membranes. This multi-functionality allows the system to achieve both low energy losses and high power density simultaneously.
2Loss of energy
If ion exchange membranes are used as separators in non-aqueous redox flow batteries, then ionic conductivity is provided for minimizing losses due to resistance to current flow, but the cost increases and the membrane contributes to approximately 20% of the battery cost
Solution Approach 1:
The patent replaces expensive ion exchange membranes with cheaper size-exclusion membranes that can be manufactured more economically. This substitution directly addresses the cost issue while maintaining the necessary ionic conductivity function, thereby resolving the contradiction between minimizing energy losses and reducing battery cost.
3Power
If redox active particles are allowed to pass through the separating membrane, then ionic conductivity is maintained, but crossover of redox active particles occurs which lowers power and current density and affects overall performance by enabling Coulombic losses
Solution Approach 1:
The patent applies different properties to different parts of the membrane system: the size-exclusion membrane has pore sizes that are large enough to allow ion transport but small enough to prevent redox particle crossover. This local differentiation of transport properties resolves the contradiction between maintaining power density and preventing Coulombic losses.
Solution Approach 2:
The patent utilizes porous size-exclusion membranes with specifically controlled pore sizes and distributions. These porous structures enable selective transport based on particle size, allowing ions to pass while blocking larger redox particles, thereby simultaneously maintaining power density and preventing crossover losses.
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 approach significantly reduces redox active particle crossover, increasing energy density and power while reducing costs by using less expensive size-exclusion membranes, achieving higher electrochemical activity and stability in non-aqueous redox flow batteries.
Implementation Method 1
a size exclusion membrane that allows counter ions to pass through but prevent or substantially prevents the crossover of the redox active polymers and colloidal particles
Implementation Method 2
electrochemical energy is stored in highly concentrated solutions of reversible redox active molecules
Data Source
AI summary
The invention provides a redox flow battery comprising a microporous or nanoporous size-exclusion membrane, wherein one cell of the battery contains a redox-active polymer dissolved in the non-aqueous solvent or a redox-active colloidal particle dispersed in the non-aqueous solvent. The redox flow battery provides enhanced ionic conductivity across the electrolyte separator and reduced redox-active species crossover, thereby improving the performance and enabling widespread utilization. Redox active poly(vinylbenzyl ethylviologen) (RAPs) and redox active colloidal particles (RACs) were prepared and were found to be highly effective redox species. Controlled potential bulk electrolysis indicates that 94-99% of the nominal charge on different RAPs is accessible and the electrolysis products are stable upon cycling. The high concentration attainable (>2.0 M) for RAPs in common non-aqueous battery solvents, their electrochemical and chemical reversibility, and their hindered transport across porous separators make them attractive materials for non-aqueous redox flow batteries based on size-selectivity.