ZAS has covered the full value chain from material production, component building, cell assembly, testing and module design of ZABs. An evaluation of the potential for integration of these modules into a hybridised energy storage system has also been conducted. The project has been constructed around a few key activities, which are closely linked as illustrated in Figure 2.
Electrolytes:
It has been demonstrated that improved cycling properties can be obtained by introducing specific additives in to the alkaline electrolyte as shown in Figure 3. In addition, alternative near neutral electrolyte compositions have been tested and optimized. A strength in the project has been the close collaboration between the modelling and experimental activity, resulting in a good understanding of how the electrolyte components interact and hence how the electrolyte may be improved. Figure 4 shows a schematic of the chlorine based near-neutral electrolyte investigated.
Cathode Development:
A high performing bifunctional air electrode (cathode) needs a bifunctional catalyst which is active both during charging and discharging. Numerical screening methods based on density functional theory (DFT) have reduced the number of catalysts that were necessary to test experimentally, as illustrated in Figure 5. An important achievement in the project has been the development of a non-carbon bifunctional electrode.
Anode Development:
Continuum-scale models have been used to understand how the operating conditions and e.g. the thickness of the Zn anode influence passivation mechanisms of the electrode as illustrated in Figure 6. Zinc-paste containing small amounts of bismuth and indium showed good cyclability in an optimized electrolyte. DFT calculations combined with differential electrochemical mass spectrometry measurements (DEMS) were used to explain this as these dopants were found to lower the overpotential during discharge and prevent hydrogen evolution.
Cell Design:
In ZAS, different types of battery cells have been used; from small lab cells (1cm2) for testing and optimizing materials, pilot scale cells (25cm2) for optimization of operating conditions and long-term tests, and a demonstrator cell (182cm2) for verifying operation under realistic conditions. Long-term tests have shown that the ZAB developed in ZAS can be operated for at least 2000 hours/200 cycles. Half-cell tests, in which the anode and cathode have been tested separately, have shown that they can operate properly for at least 1000 cycles.
Application of ZAS Technology:
The developed ZAS technology has been theoretically evaluated to cover typical energy storage applications like smoothing, firming and load shifting when integrated with a 500 kWP PV Plant. Among all the large-scale energy storage scenarios evaluated, load shifting is found to be the one most suitable for implementing the ZAS technology. A "Cradle to Gate" Life Cycle Analysis (LCA) has been completed and shows that production of ZABs has the potential for considerably less CO2 emissions than other battery technologies like LIB.
Exploitation and dissemination:
10 peer-reviewed publications, 4 PhD thesis, 4 patens, conference contributions, mass media.
ZAS hosted an Early stage researcher seminar on Zinc based batteries in Ulm, Germany, June 2017 and the 2nd International Zinc-Air Battery Workshop (IZABW2) in Trondheim, Norway, April 2018.
