Periodic Reporting for period 2 - Bi3BoostFlowBat (Bioinspired, biphasic and bipolar flow batteries with boosters for sustainable large-scale energy storage)
Reporting period: 2022-07-01 to 2023-12-31
To satisfy our growing energy demand while reducing reliance on fossil fuels, a switch to renewable energy sources is vital. The intermittent nature of the latter means innovations in energy storage technology is a key grand challenge. Cost and sustainability issues currently limit the widespread use of electrochemical energy storage technologies, such as lithium ion and flow batteries. As the scale for energy storage is simply enormous, the only option is to look for abundant materials. However, compounds that fulfil the extensive requirements entailed at low cost has yet to be reported. While it is possible that the holy grail of energy storage will be found, for example by advanced computational tools and machine learning to design “perfect” abundant molecules, a more flexible, innovative solution to sustainable and cost-effective large-scale energy storage is required. Bi3BoostFlowBat will develop game changing strategies to widen the choice of compounds utilizable for batteries to simultaneously satisfy the requirements for low cost, optimal redox potentials, high solubility and stability in all conditions. The aim of this project is to develop cost-efficient batteries by using solid boosters and by eliminating cross over. Two approaches will be pursued for cross-over elimination 1) bio-inspired polymer batteries, where cross-over of solubilized polymers is prevented by size-exclusion membranes and 2) biphasic emulsion flow batteries, where redox species are transferred to oil phase droplets upon charge. Third research direction focuses on systems to maintain a pH gradient, to allow operation of differential pH systems to improve the cell voltages. Limits of different approaches will be explored by taking an electrochemical engineering approach to model the performance of different systems and by validating the models experimentally. This work will chart the route towards the future third generation battery technologies for the large-scale energy storage. Thus, the research objectives of Bi3BoostFlowBat are to: 1) Develop strategies to widen the choice of molecules utilizable for flow batteries 2) Electrochemical engineering of solid booster based flow battery systems 3) Chart the parameter space for the future third generation battery technologies
Model of porous redox active solids with the redox electrolytes was implemented in COMSOL Multiphysics. Thermodynamics and kinetics of such systems were formulated, resulting in one article. The basis of the system was earlier models of Li-ion batteries employing redox active solids, so the implementation was verified with modelling of Li-ion battery, including a sensitivity analysis. General finite element models for solid boosters on the electrode in the presence and absence of redox mediators was developed to understand the electrochemical response of the different techniques (cyclic voltammetry, potential step, current step etc. at both macro- and microelectrodes). This will allow determining what techniques are useful to characterize the soluble redox mediator-redox active solid –couples. The model was utilized in understanding scanning electrochemical microscopy experiments to gain insight on how charge transfer between redox electrolyte and redox solid takes place. This information will help to better design the system.
For the experimental part, first reactor set-up with different redox sensors has been constructed and the measurements have been performed with model redox couples. We have also focused on developing experimental set-ups for reproducible flow battery testing. As major achievement, testing capability for up to 16 batteries simultaneously has been achieved. Initial testing of bipolar membranes has been performed, but results for utilizing differential pH batteries are not promising. Unfortunately, the idea of pH gradient generation with another cell was published by another group. Development of lignosulfonate based polymeric redox species has started, focusing on demethylation of OMe groups.
Biphasic systems for flow batteries have been explored. We have shown that it is possible to increase the cell voltage of biphasic flow battery significantly, by more than 0.5 V by utilizing Galvani potential difference between the two phases. However, interfacial charge transfer results in significant self-discharge, and efforts to realize low resistance cell have been challenging. Porous membranes tend to allow one phase to pass through, resulting in cross-over. Best results have been achieved with conventional ion exchange membranes, indicating that it will be difficult to realize a membraneless system.
For the experimental part, first reactor set-up with different redox sensors has been constructed and the measurements have been performed with model redox couples. We have also focused on developing experimental set-ups for reproducible flow battery testing. As major achievement, testing capability for up to 16 batteries simultaneously has been achieved. Initial testing of bipolar membranes has been performed, but results for utilizing differential pH batteries are not promising. Unfortunately, the idea of pH gradient generation with another cell was published by another group. Development of lignosulfonate based polymeric redox species has started, focusing on demethylation of OMe groups.
Biphasic systems for flow batteries have been explored. We have shown that it is possible to increase the cell voltage of biphasic flow battery significantly, by more than 0.5 V by utilizing Galvani potential difference between the two phases. However, interfacial charge transfer results in significant self-discharge, and efforts to realize low resistance cell have been challenging. Porous membranes tend to allow one phase to pass through, resulting in cross-over. Best results have been achieved with conventional ion exchange membranes, indicating that it will be difficult to realize a membraneless system.
For solid boosters, thermodynamics and kinetics were formulated, giving insight on how to realize practical systems. General finite element models for solid boosters on the electrode in the presence and absence of redox mediators was developed to understand the electrochemical response of the different techniques (cyclic voltammetry, potential step, current step etc. at both macro- and microelectrodes). This will allow determining what techniques are useful to characterize the soluble redox mediator-redox active solid –couples. The model was utilized in understanding scanning electrochemical microscopy experiments to gain insight on how charge transfer between redox electrolyte and redox solid takes place. This information will help to better design the system.
Biphasic systems for flow batteries have been explored. We have shown that it is possible to increase the cell voltage of biphasic flow battery significantly, by more than 0.5 V by utilizing Galvani potential difference between the two phases. This is the first time such as system has been demonstrated.
I expect that the project will provide a roadmap of conditions where the technologies investigated (bipolar membrane based flow batteries, biphasic flow batteries and lignosulfonate based flow batteries) would be feasible.
Biphasic systems for flow batteries have been explored. We have shown that it is possible to increase the cell voltage of biphasic flow battery significantly, by more than 0.5 V by utilizing Galvani potential difference between the two phases. This is the first time such as system has been demonstrated.
I expect that the project will provide a roadmap of conditions where the technologies investigated (bipolar membrane based flow batteries, biphasic flow batteries and lignosulfonate based flow batteries) would be feasible.