Future of Electrochemical Energy Storage
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several companies are promoting prototypes of SIBs for commercialization, SIBs are mainly challenged by intrinsically low specific energy density compared to the that of LIBs; in addition, the safety of SIBs has not been fully verified. In addition to rechargeable batteries, supercapacitors having high power capability and long life are increasingly recognized as an alternative power source. In a recent issue of ACS Energy Letters, Kong and co-workers3 developed a symmetric supercapacitor with a very high volumetric energy density, introducing a new set of opportunities for developing a supercapacitor material with a high-energy density. We expect to see more advanced energy storage devices with new technologies in the future.
he commercial Li-ion batteries (LIBs) in mobile electronic devices have been a key component leading to the wide acceptance of digital communication which has already fundamentally changed the way we exchange information. The foreseeable depletion of fossil fuel reserves and the need for reduction of CO2 emissions are now driving the efforts to extend the success of LIBs from small electronic devices to electric vehicles and large-format energy storage systems. Despite impressive innovations, the current LIB technology is, however, yet to satisfactorily meet the demands of these mid- to large-scale applications. In particular, as the battery modules become increasingly larger, specific energy density, cost, and safety are key issues to be resolved. At present, the overall performance of the LIBs is largely limited by the cathode, which is the most expensive and heaviest component in a LIB. Over the years, various combinations of cathode compositions in the layered LiNi1−x−yCox(Al or Mn)yO2 materials have been proposed, and the LiNi1−x−yCoxAlyO2 cathodes have reached the stage where the cathodes can be safely and cost-effectively used for powering electric vehicles. In a previous issue of ACS Energy Letters, Myung et al.1 reported the potentials and limitations of Ni-rich LiNi1−x−yCox(Al or Mn)yO2 cathodes with emphasis on realistically meeting the target values from general electromobility. Although the future of the Ni-rich LiNi1−x−yCox(Al or Mn)yO2 cathodes looks bright, the surface modification, introduction of compositional gradients, and coating and doping are still necessary to address battery safety for successful commercialization of Ni-rich layered cathodes. In addition to the LIBs, Li−S, Li−air, and Na-ion batteries have also attracted much attention as competing battery technology because of their potentially high specific energy density and low price. The Li−S batteries, offering high specific density of 1675 mA h g−1 and low material cost, are a promising next-generation batteries. Host materials such as doped carbon, metal oxide, metal sulfide, etc., capable of adsorbing lithium polysulfides, have been recently proposed, but challenges such as electrode volume change and low loading level of active material still remain for commercializing the technology. In the case of the Li−air batteries, despite their highest theoretical specific energy density, poor lifetime, poor rate performance, and low volumetric capacity still make this battery system impractical for electric vehicles. Although many laboratory-scale experiments have reported significant improvements, the reproducibility and the scaling-up of the technology remain questionable. It is proposed that redox mediators (RMs) may provide a key to unlock the potential of the Li−air batteries; however, Viswanathan and Pande2 in an article in ACS Energy Letters caution that although RMs could be an efficacious approach to improving the rechargeability as well as rate capability of the Li−air batteries, these compounds should be selected carefully because of their parasitic reactions with other cell components. Sodium-ion batteries (SIBs) are also considered promising chiefly because sodium is widely available and the SIBs exhibit chemistry similar to that of LIBs. Although © 2017 American Chemical Society
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RELATED READINGS (1) Myung, S.-T.; Maglia, F.; Park, K.-J.; Yoon, C. S.; Lamp, P.; Kim, S.-J.; Sun, Y.-K. Nickel-Rich Layered Cathode Materials for Automotive Lithium-Ion Batteries: Achievements and Perspectives. ACS Energy Lett. 2017, 2, 196−223. DOI: 10.1021/acsenergylett.6b00594. (2) Pande, V.; Viswanathan, V. Criteria and Considerations for the Selection of Redox Mediators in Nonaqueous Li−O2 Batteries. ACS Energy Lett. 2017, 2, 60−63. DOI: 10.1021/ acsenergylett.6b00619. (3) Zhang, W.-B.; Ma, X.-J.; Loh, A.; Li, X.; Walsh, F. C.; Kong, L.-B. High Volumetric Energy Density Capacitors Based on New Electrode Material Lanthanum Nitride. ACS Energy Lett. 2017, 2, 336−341. DOI: 10.1021/acsenergylett.6b00636. Yang-Kook Sun, Senior Editor, ACS Energy Letters Department of Energy Engineering, Hanyang University, Seoul 133-791, Republic of Korea
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AUTHOR INFORMATION
ORCID
Yang-Kook Sun: 0000-0002-0117-0170 Notes
Views expressed in this editorial are those of the author and not necessarily the views of the ACS.
Published: March 10, 2017 716
DOI: 10.1021/acsenergylett.7b00158 ACS Energy Lett. 2017, 2, 716−716
Editorial
http://pubs.acs.org/journal/aelccp
