Mediated Redox Flow Battery Anode for High Capacity Phosphorus Storage
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Solution Overview
Problem
High energy batteries face limitations due to large volume changes in anode materials, leading to cycle life reduction and safety concerns, and conventional redox flow batteries are limited by solubility of redox species and operating potential, resulting in low energy density and cycle life.
Innovation Solution
A mediated redox flow battery system utilizing a series of secondary organic molecules forming highly reduced anion radicals as reaction mediators, coupled with a redox flow anode chamber and an external container containing solid phosphorus, allowing for decoupling of energy density from solubility and enabling high capacity and cycle life through mediated electrochemical reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high capacity anode materials (alkali metals, alkali metal alloys) are used to achieve high energy density, then capacity is improved, but volume change during charge/discharge exceeds 300% causing pulverization and safety concerns
Solution Approach 1:
The patent divides the charge storage function into two separate components: (1) a stable anode structure that does not undergo volume change, and (2) redox-active species in electrolyte that provide high capacity. This segmentation allows the anode to remain structurally intact while the electrolyte contains the high-capacity redox materials, resolving the contradiction between high capacity and structural stability.
Solution Approach 2:
The patent introduces redox mediators (organic molecules like quinones, viologens, or metal complexes) as intermediaries to transfer charge between the stable anode and the high-capacity redox species in the electrolyte. This mediator approach enables the anode to remain structurally stable while still achieving high capacity through the redox reactions of the mediators in the electrolyte.
2Quantity of substance
If redox flow battery uses high solubility redox species to increase energy density, then capacity is improved, but operating potential is limited by electrolyte stability window
Solution Approach 1:
The patent changes the operating potential parameters by selecting redox mediators with appropriate redox potentials that fall within the stable electrolyte window. By carefully selecting mediators like quinones, viologens, or metal complexes with tunable redox potentials, the system achieves high capacity through high solubility while maintaining operation within the thermodynamic stability window of the electrolyte.
3Power
If conventional redox flow battery stores active redox materials physically in the electrochemical cell stack to achieve reasonable power density, then power density is improved, but gravimetric and volumetric energy density are lowered
Solution Approach 1:
The patent separates the energy storage function from the power delivery function by placing high-capacity redox species in the electrolyte (energy dimension) while maintaining a compact electrochemical cell stack for power delivery (power dimension). This dimensional separation allows independent optimization of energy density and power density, resolving the trade-off between storing large amounts of energy and delivering it at high power rates.
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 system achieves high energy density and cycle life by recycling anion radicals, unaffected by anode volume changes and ensuring safe operation, with capacities up to 1900 mAh/g and ability to operate at very negative potentials, significantly surpassing existing mediated RFB systems.
Implementation Method 1
During a charging cycle the first redox-active mediator is reduced at the current collector and subsequently reduces the phosphorus material. During a discharging cycle the second mediator is oxidized at the current collector, and the second redox-active mediator is then reduced by the reduced phosphorus material.
Implementation Method 2
A separator conducts one selected from the group consisting of lithium ions and sodium ions, and is coupled to the anode chamber
Data Source
AI summary
A battery includes a redox flow anode chamber coupled to an anode current collector, a separator, and an external container in fluid connection with the redox flow anode chamber. The external container has therein a solid phosphorus material. A first redox-active mediator and the second redox-active mediator are circulated through the half-cell electrode chamber and the external container. During a charging cycle the first redox-active mediator is reduced at the current collector electrode and the reduced first mediator reduces the phosphorus material, and wherein during a discharging cycle the second redox-active mediator is oxidized at the anode current collector electrode, and the second redox-active mediator is then reduced by the reduced phosphorus material. A method of operating a battery and a method of making a battery are also discussed.