Resource constraints on the battery energy storage potential for grid and transportation applications
Introduction
The rapid expansion of renewable energy has driven interest in energy storage to facilitate the widespread and large-scale deployment of intermittent, carbon-free energy sources [1], [2], [3], [4], [5]. Likewise, the future of electric vehicles (EVs) depends strongly on portable energy storage. Technologies that have been explored for various energy storage applications include pumped hydroelectric (PHE), compressed air (CAES), batteries, flywheels, and ultracapacitors [1], [6], [7], [8], [9], [10]. Constraints on new system installations vary. For example, both PHE and CAES rely on favourable geography and geology to be cost effective, and the number of new sites is limited [8], [11]. Batteries, in contrast to PHE and CAES, provide an important option for grid-scale storage because they can be sited close to demand load, reducing transmission installations and losses [12]. Furthermore, batteries are the only suitable technology for near-term deployment in EVs [13], [14]. Technology hurdles exist for batteries to meet performance targets, but of equal importance to their future use at large scales is the availability of the elements used to make the battery active materials that are combined to form battery couples (a battery couple contains anode and cathode active materials). Herein we present the first systematic analysis of limits on the availability of the elements for battery couples, providing a clear assessment of the potential to significantly scale-up battery production in the coming decades.
At present, lithium-ion, nickel metal hydride, and lead-acid batteries dominate the portable rechargeable storage markets, while sodium-sulfur and redox flow batteries have been deployed for stationary storage [15], [16], [17]. Our analysis includes these couples, as well as others that have been shown to operate reversibly (albeit at various degrees of performance and development), have current relevance in the battery markets, or are of interest to the research community. Some couples, such as Pb/PbO2 (lead-acid) and C6/LiCoO2 (lithium-ion), are widely familiar while others, such as C6/LiMnPO4 and Li/O2, are still in the research stage. With such a broad set of couples available, it is critical to identify which are suitable for grid vs. EV applications, as well as any resource limitations that set an upper bound on the energy storage potential (ESP) of each couple.
Section snippets
Methods
We define the ESP as the maximum amount of energy (in TWh) that can be stored by the complete exhaustion of the limiting element of a battery couple. We evaluate the ESP by looking at the amount of the limiting element available under two constraints: annual production and total reserve base. Annual production and total reserve base data are taken from the United States Geological Service Mineral Commodity Surveys (see Supporting Information for Detailed Information) [18]. The annual production
Evaluation of the suitability of battery couples for grid and/or electric vehicle energy storage
Batteries for grid-scale and electric vehicle energy storage have significantly different performance requirements. While all 27 couples under investigation could be deployed for grid-storage applications, only a sub-set are appropriate for EVs. For the 27 couples under investigation, Fig. 1 shows the practical system-level specific energy and the theoretical specific energy based on the weight of the active materials alone (detailed references can be found in supporting Information). The
Framework for evaluating electric vehicle couples not based on Li
Our analysis can also inform the search for EV battery couples based on non-Li couples. For example, among the couples in our present analysis, those containing Cl, Cr, Fe, Mn, Na, S, and Zn are found in couples with a particularly high ESP and have a low extraction cost; new couples utilizing these elements may be of particular interest. Mg-based couples have also been discussed as having the potential to achieve a high specific energy and eventually replace Li-based couples [38]. Fig. 1
Limitations of the present analysis and suggestions for future work
This analysis provides a best-case scenario for the battery ESP based on the availability and cost of the elements for battery active materials alone, and can therefore be thought of as a “first order” analysis. Future work can address some of the limitations of the present analysis and the questions that it raises. We list some of the most important topics here.
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The ESP analysis based on the elements in the active materials alone neglect the balance-of-system components, which in general make
Conclusions
In the short-term (10–15 years) and long-term (40–50 years) there is sufficient availability of the elements for battery deployment in grid-scale applications. For the EV application, scale-up of Li production will be needed to meet short-term goals, but will be especially necessary to meet long-term goals. Eventually, on the order of 1 billion 40 kWh Li-based EV batteries can be built with the currently estimated reserve base of Li. Achieving aggressive cost reductions will continue to be a
Acknowledgements
We would like to thank Daniel Kammen, John Newman, Craig Horne, Ilan Gur, Andrew Mills, Rebecca Jones, and Richard Jones for their contributions.
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