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Zinc Air Secondary innovative nanotech based batteries for efficient energy storage

Periodic Reporting for period 2 - ZAS (Zinc Air Secondary innovative nanotech based batteries for efficient energy storage)

Reporting period: 2016-12-01 to 2018-05-31

Zinc–air batteries (ZABs) are promising candidates for next-generation energy storage. Their basic operation principle is to electrochemically reduce oxygen gas from air and oxidize the zinc at the anode as sketched in Figure 1. By using the oxygen in the air as one of the reactants, both the volume and the weight of the battery can be significantly reduced compared to Li-ion systems. The main component of the battery is zinc, which is an abundant and non-hazardous material and is mined and processed in Europe. ZABs have also a superior operational safety characteristic. However, so far, the electrical rechargeability and calendar life of these batteries have been limited.
Due to the high energy density and use of abundant and environmentally friendly materials combined with the potential for low production costs, rechargeable ZABs would be beneficial for many different energy storage applications. I. In particular, the stationary energy storage sector is growing rapidly, and it is., used to stabilize the electrical grid when increased amount of intermittent renewable energy sources, like solar and wind, are introduced Such applications require huge batteries. On a long-term scale, Li-ion systems will probably suffer from lack of access to resources, especially if this is the only solution used for electrical storage both for the mobility sector and stationary storage. ZABs will be a cost-effective and safe alternative. Since the IPR related to ZABs to a large extent is located in Europe, it is also likely that future development and manufacturing of ZABs will remain in Europe.
In order to increase the rechargeability, the degradation mechanisms of the electrodes and electrolyte during operation have to be understood and subsequently avoided. The main objectives in the ZAS project have been to improve the performance (higher energy density, Wh/kg and Wh/L) and lifetime (number of complete charge/discharge cycles) of ZABs as well as reducing their cost (€/kWh). It has also been important to show the scalability of the technology as well as the market potential.
"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.

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.
In ZAS, there has been a strong focus on identifying and developing high performance materials and cell components for ZABs. This has resulted in progress beyond state of the art in the following fields:
• Development of a Multi-Scale Modeling Platform with an integrated approach going from DFT calculations up to continuum models as illustrated in Figure 7.
• Better understanding of how alkaline and near-neutral electrolyte compositions impact the overall performance of the electrodes during charge and discharge by combining numerical modeling with experimental tests.
• Developed a DFT based method for efficient screening of oxide-based catalysts for ZABs, hence accelerating development in the field.
• Built fundamental knowledge related to the role of additives like bismuth and indium in the zinc anode and how they reduce the risk of passivation and hydrogen evolution. This knowledge has been used to further optimize the composition of the anode as well as to predict how the anode should be structured.

Short and long-term impacts of ZAS:
• ZAS has been one of the first European projects to attempt to design a Multi-Scale Modeling Platform in the field of batteries. The Platform established in ZAS will have relevance also for other battery chemistries and will have a significant impact on further development and the design of batteries.
• The knowledge gained around the role of the electrolyte and understanding of how the thermodynamics of electrolyte works can be extended and utilized for other battery chemistries and fuel cells.
• Development of sustainable and environmentally friendly alternatives to Li-ion batteries for stationary energy storage will be important in a long-term perspective. The strong competence built in ZAS (including 4 patents) will contribute to the fact that crucial knowledge for building the next generation of electricity storage systems will remain in Europe.
Passivating the zinc-electrode by the formation of dense ZnO(II).
Schematic of the chlorine based electrolyte investigated in ZAS.
Sketch of the zinc-air battery.
Screening of key parameters like conductivity, stability and activity of bifunctional catalysts
Work flow chart of the ZAS project. Covering the full value chain from material production up to mod
Cycle life map of a full zinc-air cell as a function of KOH and additives concentration.
An illustration of the Integrating Multi-Scale Modeling Platform developed in ZAS .