- Email: [email protected]
Beyond Photovoltaic Lab Efficiency
amine sites react with CO2 molecules giving carbamates, which are further reduced to CO by accepting electrons from the silver electrode. Thus, the synergistic combination of metallic substrate and CO2-favorable amine COF affords high efficiency and selectivity in electrochemical CO2 conversion. This work represents an important advance in COF chemistry and has produced highly stable COFs with enhanced performance on electrochemical CO2 reduction to CO. For a direct impact, the modification method reported here will serve as a guide for continued exploration of stable COFs for various applications. Second, the introduction of amine and the approach of porous framework/metal composites for electrochemical CO2 conversion provide a new way to access novel electrochemical catalysts with high effi-
ciency and selectivity. Moving forward, future efforts to thoroughly understand the electrocatalytic process of CO2 conversion and for controllable reduction to high-value carbon products will be initiated by this advance. 1. Chu, S., Cui, Y., and Liu, N. (2016). The path towards sustainable energy. Nat. Mater. 16, 16–22.
platforms for functional materials. Acc. Chem. Res. 49, 483–493. 6. Liao, P.-Q., Shen, J.-Q., and Zhang, J.-P. (2017). Metal–organic frameworks for electrocatalysis. Coord. Chem. Rev. Published online September 20, 2017. https://doi.org/10.1016/j.ccr.2017.1009.1001. 7. Trickett, C.A., Helal, A., Al-Maythalony, B.A., Yamani, Z.H., Cordova, K.E., and Yaghi, O.M. (2017). The chemistry of metal–organic frameworks for CO2 capture, regeneration and conversion. Nat. Rev. Mater. 2, 17045.
2. Bushuyev, O.S., De Luna, P., Dinh, C.T., Tao, L., Saur, G., van de Lagemaat, J., Kelley, S.O., and Sargent, E.H. (2018). What should we make with CO2 and how can we make it? Joule 2, 825–832.
8. Diercks, C.S., Liu, Y., Cordova, K.E., and Yaghi, O.M. (2018). The role of reticular chemistry in the design of CO2 reduction catalysts. Nat. Mater. 17, 301–307.
3. Qiao, J., Liu, Y., Hong, F., and Zhang, J. (2014). A review of catalysts for the electroreduction of carbon dioxide to produce low-carbon fuels. Chem. Soc. Rev. 43, 631–675.
9. Lin, S., Diercks, C.S., Zhang, Y.-B., Kornienko, N., Nichols, E.M., Zhao, Y., Paris, A.R., Kim, D., Yang, P., Yaghi, O.M., and Chang, C.J. (2015). Covalent organic frameworks comprising cobalt porphyrins for catalytic CO2 reduction in water. Science 349, 1208–1213.
4. Li, B., Wen, H.M., Cui, Y., Zhou, W., Qian, G., and Chen, B. (2016). Emerging multifunctional metal-organic framework materials. Adv. Mater. 28, 8819–8860. 5. Cui, Y., Li, B., He, H., Zhou, W., Chen, B., and Qian, G. (2016). Metal-organic frameworks as
10. Liu, H., Chu, J., Yin, Z., Cai, X., Zhuang, L., and Deng, H. (2018). Covalent organic frameworks linked by amine bond for concerted electrochemical reduction of CO2. Chem 4. .Published online June 14, 2018. https://doi.org/10.1016/j.chempr.2018. 05.002.
Preview
Beyond Photovoltaic Lab Efficiency Brandon R. Sutherland1,* Solar cell development has focused heavily on improving the efficiency under a standard reference spectrum representative of temperate climates. These conditions are rarely met in the field. In this issue of Joule, Peters and Buonassisi use open-source atmospheric satellite data to predict the electricity produced from a solar cell of given bandgap installed at any location globally. The intensity and spectral distribution of solar radiation incident on the Earth’s surface is not a constant. It is a complex function of the local terrestrial atmospheric conditions, temperature, and relative angle of the sun to a given surface on Earth. Devices that harvest sunlight, such as a solar cell, have performance metrics that vary wildly depending on date, time, weather, and location. In the early 90s the Amer-
ican Society for Testing and Materials worked with the photovoltaic industry to develop a reference sunlight spectrum for the evaluation of solar cell performance. Last updated in January 2003, this spectrum (ASTM G-173-03)1 represents an approximate yearly average of the continental United States and is now adopted as the global standard. Artificial light sources that mimic this spectrum are widely available.
1032 Joule 2, 1028–1038, June 20, 2018 ª 2018 Published by Elsevier Inc.
Photovoltaics continue to be the fastest-growing source of new energy production. In 2017, there was a record 98 GW of new solar power commissions, outpacing all new fossil fuel capacity additions by 28 GW.2 Commercial solar cells are primarily based on silicon, which exceeds 90% market share.3 Research in new photovoltaic materials is fighting uphill against a rapidly growing industry. The lab-scale development of new solar cells almost entirely focuses on maximizing power conversion efficiency (PCE)—the electrical power the cell provides per amount of optical power from the sun it captures—using an approximation of the ASTM G-173-03 standard for sunlight. This trend was largely influenced
1Joule,
Cell Press, 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, USA *Correspondence: [email protected] https://doi.org/10.1016/j.joule.2018.06.001
Figure 1. Global Energy Yield Limit The yearly energy yield in kWh/m 2 of a single-junction solar cell with an ideal bandgap across the globe. Data based on NASA open-source satellite data; see formatted supplemental file S1. 8
by the seminal calculations of Shockley and Queisser in the early 1960s.4 Today, the PCE of a solar cell is at the heart of all new device research,5 with the latest exciting values being referenced in every paper and talk. Emerging solar cells are based on materials that possess a range of bandgaps—the minimum energy of light they can absorb. Most of these materials possess bandgaps larger than silicon. The response of a solar cell is well known to vary with temperature,6 something that most models now incorporate. A lesser-studied effect is the quantitative role that precipitate water in the atmosphere has in determining bandgap-dependent cell performance. Recently, this was incorporated into a robust model for predicting field performance of a solar cell using global satellite data.7 While convenient for lab-to-lab comparisons, commercialscale deployment of solar cell modules must think beyond ideal reference spectra, which are rarely relevant in real-world installations, and consider performance in local climates. The cost of solar-cell-provided electricity is almost entirely accounted for by the initial investment and the
amount of electricity that is produced over the lifetime of the plant. Accurately predicting yearly performance at a deployment location is therefore critical to estimate the economic viability of any new solar power plant. The energy yield of a solar cell describes the amount of power produced over time under operating conditions, normalized to area. Accurately predicting the energy yield at the installation site requires correlating the atmospheric dependence of a given solar material to the local conditions. In this issue of Joule, Peters and Buonassisi have used open-source satellite data from NASA to calculate and understand the yearly energy yield limits of promising solar cell materials across the globe.8 Approximately two-thirds of all solar capacity through 2015 has been installed in temperate climates, such as Europe, Japan, and North America.3 Not surprisingly, most existing solar field performance studies and models focus on these traditional markets. However, more than half of new solar installations are expected to be in tropical and subtropical regions by the end of this decade.3 In these climates, estimating the value of a solar cell using standard-
ized power conversion efficiencies is especially inadequate. Here, the authors adapted a detailed balance model coupled to open-source satellite data to approximate the energy yield limits of a solar cell based on its labmeasured solar cell efficiency and bandgap. They found that the difference between lab-measured standardized efficiencies and the median of the statistical distribution of real-world harvesting efficiencies is a simple linear function of the solar-absorbing material’s bandgap. Generally, as the bandgap decreases, standardized power conversion efficiencies progressively overestimate the actual outdoor performance. This is a result of increased sensitivity to atmospheric water absorption and temperature for smaller bandgap materials. Mapping the global energy yield limits for an ideal bandgap material (Figure 1) reveals that there is strong correlation with the distribution of standard Ko¨ppen-Geiger climate zones. This work enables researchers developing new solar-harvesting materials of varying bandgap to accurately compare their results on a fair basis and predict their potential for field harvesting efficiency. When developing new photovoltaic materials, instead of focusing solely on maximizing PCE under standard conditions, one should consider maximizing the energy yield (and doing so in the most commercially relevant areas). As an example, replacing the Pb metal cation in perovskites with less toxic Sn can shift the bandgap towards a value with a more favorable theoretical maximum PCE, but at the cost of reduced stability.9 In contrast, reduced-dimensional perovskites exhibit increased intrinsic stability, but have bandgaps further from the single-junction performance maximum.10 There are many such examples of performance/stability tradeoffs in solar research. The problem is that the conversations people have about these tradeoffs solely concern power conversion efficiency under standard
Joule 2, 1028–1038, June 20, 2018 1033
reference spectra, intrinsically disconnecting them with their prospective applications. Using the framework developed in this paper, a solar cell researcher could determine what kind of energy yield loss they expect by increasing their bandgap, and weigh that against the potential upsides (such as improved stability). Future work could extend this approach to multi-junction solar cells, particularly as low-cost alternatives such as perovskite/perovskite and perovskite/silicon tandems enter early commercial considerations.11,12 Anecdotally, I’d wager that more people can tell you the record power conversion efficiency of the solar cell material they are working on than could even define what energy yield is. Next time a PV researcher is promoting their power conversion efficiency, for fun, ask them what the expected energy
yield is. Maybe it will spur interest in the research community for more application-oriented thinking at all scales of development. 1. ASTM G173-03(2012). (2012). Standard Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37 Tilted Surface (ASTM International). www.astm.org. 2. Global Trends in Renewable Energy Investment. (2018). Frankfurt School of Finance & Management. http://www.fsunep-centre.org/. 3. Photovoltaics Report. (2017). Fraunhofer Institute for Solar Energy Systems. https:// www.ise.fraunhofer.de/content/dam/ise/de/ documents/publications/studies/ Photovoltaics-Report.pdf. 4. Shockley, W., and Queisser, H.J. (1961). Detailed Balance Limit of Efficiency of p-n Junction Solar Cells. J. Appl. Physiol. 32, 510–519. 5. Green, M.A., Hishikawa, Y., Dunlop, E.D., Levi, D.H., Hohl-Ebinger, J., and Ho-Baillie, A.W.Y. (2018). Solar cell efficiency tables (version 51). Prog. Photovolt. Res. Appl. 26, 3–12.
6. Green, M.A. (2003). General temperature dependence of solar cell performance and implications for device modelling. Prog. Photovolt. Res. Appl. 11, 333–340. 7. Peters, I.M., Liu, H., Reindl, T., and Buonassisi, T. (2018). Global Prediction of Photovoltaic Field Performance Differences Using Open-Source Satellite Data. Joule 2, 307–322. 8. Peters, I.M., and Buonassisi, T. (2018). Energy Yield Limits for Single-Junction Solar Cells. Joule 2, this issue, 1160–1170. 9. Abate, A. (2017). Perovskite Solar Cells Go Lead Free. Joule 1, 659–664. 10. Quan, L.N., Yuan, M., Comin, R., Voznyy, O., Beauregard, E.M., Hoogland, S., Buin, A., Kirmani, A.R., Zhao, K., Amassian, A., et al. (2016). Ligand-Stabilized ReducedDimensionality Perovskites. J. Am. Chem. Soc. 138, 2649–2655. 11. Anaya, M., Lozano, G., Calvo, M.E., and Mı´guez, H. (2017). ABX 3 Perovskites for Tandem Solar Cells. Joule 1, 769–793. 12. Werner, J., Niesen, B., and Ballif, C. (2018). Perovskite/Silicon Tandem Solar Cells: Marriage of Convenience or True Love Story? - An Overview. Adv. Mater. Interfaces 5, 1700731.
Preview
Taking the Positive with the Negative Rahul Malik1,* In this issue of Joule, Haoshen Zhou, Shaohua Guo, and colleagues reveal a layered transition metal oxide cathode material that can sequentially intercalate alkali cations and anions, together contributing a capacity exceeding the traditionally defined theoretical limit by more than one third. The authors demonstrate a new concept of cationic and anionic co-(de)intercalation in P3-Na0.5Ni0.25Mn0.75O2, a sodium ion cathode material with 134 mAh g 1 theoretical capacity based on complete Na extraction, but here shown to be capable of delivering 180 mAh g 1 reversible capacity (at 20 mA g 1) through the additional intercalation of anions from the electrolyte. The notion that improving battery technology is a critical driver of human prosperity is steadily gaining traction in the public consciousness, and increasingly recognized far beyond the confines of the battery research com-
munity. Not only do savvy consumers recognize that ‘‘better batteries mean better products,’’ but they also appreciate that the technology ‘‘is frustratingly slow to advance, due to both the chemical processes involved
1034 Joule 2, 1028–1038, June 20, 2018 ª 2018 Published by Elsevier Inc.
and the challenges that exist around commercializing new battery designs.’’1 Modern lithium ion batteries have proven effective at storing energy through the reversible intercalation of lithium into host crystal structures of active electrode materials—usually a graphitic carbon anode and a layered transition metal oxide cathode, respectively. The ‘‘rocking chair’’ design, based on shuttling the guest alkali species (Li) from cathode to anode upon charge, and the reverse during discharge, is the basis for powering modern portable electronics and electric vehicles.2
1Joule,
Cell Press, 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, USA *Correspondence: [email protected] https://doi.org/10.1016/j.joule.2018.06.002
ciency and selectivity. Moving forward, future efforts to thoroughly understand the electrocatalytic process of CO2 conversion and for controllable reduction to high-value carbon products will be initiated by this advance. 1. Chu, S., Cui, Y., and Liu, N. (2016). The path towards sustainable energy. Nat. Mater. 16, 16–22.
platforms for functional materials. Acc. Chem. Res. 49, 483–493. 6. Liao, P.-Q., Shen, J.-Q., and Zhang, J.-P. (2017). Metal–organic frameworks for electrocatalysis. Coord. Chem. Rev. Published online September 20, 2017. https://doi.org/10.1016/j.ccr.2017.1009.1001. 7. Trickett, C.A., Helal, A., Al-Maythalony, B.A., Yamani, Z.H., Cordova, K.E., and Yaghi, O.M. (2017). The chemistry of metal–organic frameworks for CO2 capture, regeneration and conversion. Nat. Rev. Mater. 2, 17045.
2. Bushuyev, O.S., De Luna, P., Dinh, C.T., Tao, L., Saur, G., van de Lagemaat, J., Kelley, S.O., and Sargent, E.H. (2018). What should we make with CO2 and how can we make it? Joule 2, 825–832.
8. Diercks, C.S., Liu, Y., Cordova, K.E., and Yaghi, O.M. (2018). The role of reticular chemistry in the design of CO2 reduction catalysts. Nat. Mater. 17, 301–307.
3. Qiao, J., Liu, Y., Hong, F., and Zhang, J. (2014). A review of catalysts for the electroreduction of carbon dioxide to produce low-carbon fuels. Chem. Soc. Rev. 43, 631–675.
9. Lin, S., Diercks, C.S., Zhang, Y.-B., Kornienko, N., Nichols, E.M., Zhao, Y., Paris, A.R., Kim, D., Yang, P., Yaghi, O.M., and Chang, C.J. (2015). Covalent organic frameworks comprising cobalt porphyrins for catalytic CO2 reduction in water. Science 349, 1208–1213.
4. Li, B., Wen, H.M., Cui, Y., Zhou, W., Qian, G., and Chen, B. (2016). Emerging multifunctional metal-organic framework materials. Adv. Mater. 28, 8819–8860. 5. Cui, Y., Li, B., He, H., Zhou, W., Chen, B., and Qian, G. (2016). Metal-organic frameworks as
10. Liu, H., Chu, J., Yin, Z., Cai, X., Zhuang, L., and Deng, H. (2018). Covalent organic frameworks linked by amine bond for concerted electrochemical reduction of CO2. Chem 4. .Published online June 14, 2018. https://doi.org/10.1016/j.chempr.2018. 05.002.
Preview
Beyond Photovoltaic Lab Efficiency Brandon R. Sutherland1,* Solar cell development has focused heavily on improving the efficiency under a standard reference spectrum representative of temperate climates. These conditions are rarely met in the field. In this issue of Joule, Peters and Buonassisi use open-source atmospheric satellite data to predict the electricity produced from a solar cell of given bandgap installed at any location globally. The intensity and spectral distribution of solar radiation incident on the Earth’s surface is not a constant. It is a complex function of the local terrestrial atmospheric conditions, temperature, and relative angle of the sun to a given surface on Earth. Devices that harvest sunlight, such as a solar cell, have performance metrics that vary wildly depending on date, time, weather, and location. In the early 90s the Amer-
ican Society for Testing and Materials worked with the photovoltaic industry to develop a reference sunlight spectrum for the evaluation of solar cell performance. Last updated in January 2003, this spectrum (ASTM G-173-03)1 represents an approximate yearly average of the continental United States and is now adopted as the global standard. Artificial light sources that mimic this spectrum are widely available.
1032 Joule 2, 1028–1038, June 20, 2018 ª 2018 Published by Elsevier Inc.
Photovoltaics continue to be the fastest-growing source of new energy production. In 2017, there was a record 98 GW of new solar power commissions, outpacing all new fossil fuel capacity additions by 28 GW.2 Commercial solar cells are primarily based on silicon, which exceeds 90% market share.3 Research in new photovoltaic materials is fighting uphill against a rapidly growing industry. The lab-scale development of new solar cells almost entirely focuses on maximizing power conversion efficiency (PCE)—the electrical power the cell provides per amount of optical power from the sun it captures—using an approximation of the ASTM G-173-03 standard for sunlight. This trend was largely influenced
1Joule,
Cell Press, 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, USA *Correspondence: [email protected] https://doi.org/10.1016/j.joule.2018.06.001
Figure 1. Global Energy Yield Limit The yearly energy yield in kWh/m 2 of a single-junction solar cell with an ideal bandgap across the globe. Data based on NASA open-source satellite data; see formatted supplemental file S1. 8
by the seminal calculations of Shockley and Queisser in the early 1960s.4 Today, the PCE of a solar cell is at the heart of all new device research,5 with the latest exciting values being referenced in every paper and talk. Emerging solar cells are based on materials that possess a range of bandgaps—the minimum energy of light they can absorb. Most of these materials possess bandgaps larger than silicon. The response of a solar cell is well known to vary with temperature,6 something that most models now incorporate. A lesser-studied effect is the quantitative role that precipitate water in the atmosphere has in determining bandgap-dependent cell performance. Recently, this was incorporated into a robust model for predicting field performance of a solar cell using global satellite data.7 While convenient for lab-to-lab comparisons, commercialscale deployment of solar cell modules must think beyond ideal reference spectra, which are rarely relevant in real-world installations, and consider performance in local climates. The cost of solar-cell-provided electricity is almost entirely accounted for by the initial investment and the
amount of electricity that is produced over the lifetime of the plant. Accurately predicting yearly performance at a deployment location is therefore critical to estimate the economic viability of any new solar power plant. The energy yield of a solar cell describes the amount of power produced over time under operating conditions, normalized to area. Accurately predicting the energy yield at the installation site requires correlating the atmospheric dependence of a given solar material to the local conditions. In this issue of Joule, Peters and Buonassisi have used open-source satellite data from NASA to calculate and understand the yearly energy yield limits of promising solar cell materials across the globe.8 Approximately two-thirds of all solar capacity through 2015 has been installed in temperate climates, such as Europe, Japan, and North America.3 Not surprisingly, most existing solar field performance studies and models focus on these traditional markets. However, more than half of new solar installations are expected to be in tropical and subtropical regions by the end of this decade.3 In these climates, estimating the value of a solar cell using standard-
ized power conversion efficiencies is especially inadequate. Here, the authors adapted a detailed balance model coupled to open-source satellite data to approximate the energy yield limits of a solar cell based on its labmeasured solar cell efficiency and bandgap. They found that the difference between lab-measured standardized efficiencies and the median of the statistical distribution of real-world harvesting efficiencies is a simple linear function of the solar-absorbing material’s bandgap. Generally, as the bandgap decreases, standardized power conversion efficiencies progressively overestimate the actual outdoor performance. This is a result of increased sensitivity to atmospheric water absorption and temperature for smaller bandgap materials. Mapping the global energy yield limits for an ideal bandgap material (Figure 1) reveals that there is strong correlation with the distribution of standard Ko¨ppen-Geiger climate zones. This work enables researchers developing new solar-harvesting materials of varying bandgap to accurately compare their results on a fair basis and predict their potential for field harvesting efficiency. When developing new photovoltaic materials, instead of focusing solely on maximizing PCE under standard conditions, one should consider maximizing the energy yield (and doing so in the most commercially relevant areas). As an example, replacing the Pb metal cation in perovskites with less toxic Sn can shift the bandgap towards a value with a more favorable theoretical maximum PCE, but at the cost of reduced stability.9 In contrast, reduced-dimensional perovskites exhibit increased intrinsic stability, but have bandgaps further from the single-junction performance maximum.10 There are many such examples of performance/stability tradeoffs in solar research. The problem is that the conversations people have about these tradeoffs solely concern power conversion efficiency under standard
Joule 2, 1028–1038, June 20, 2018 1033
reference spectra, intrinsically disconnecting them with their prospective applications. Using the framework developed in this paper, a solar cell researcher could determine what kind of energy yield loss they expect by increasing their bandgap, and weigh that against the potential upsides (such as improved stability). Future work could extend this approach to multi-junction solar cells, particularly as low-cost alternatives such as perovskite/perovskite and perovskite/silicon tandems enter early commercial considerations.11,12 Anecdotally, I’d wager that more people can tell you the record power conversion efficiency of the solar cell material they are working on than could even define what energy yield is. Next time a PV researcher is promoting their power conversion efficiency, for fun, ask them what the expected energy
yield is. Maybe it will spur interest in the research community for more application-oriented thinking at all scales of development. 1. ASTM G173-03(2012). (2012). Standard Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37 Tilted Surface (ASTM International). www.astm.org. 2. Global Trends in Renewable Energy Investment. (2018). Frankfurt School of Finance & Management. http://www.fsunep-centre.org/. 3. Photovoltaics Report. (2017). Fraunhofer Institute for Solar Energy Systems. https:// www.ise.fraunhofer.de/content/dam/ise/de/ documents/publications/studies/ Photovoltaics-Report.pdf. 4. Shockley, W., and Queisser, H.J. (1961). Detailed Balance Limit of Efficiency of p-n Junction Solar Cells. J. Appl. Physiol. 32, 510–519. 5. Green, M.A., Hishikawa, Y., Dunlop, E.D., Levi, D.H., Hohl-Ebinger, J., and Ho-Baillie, A.W.Y. (2018). Solar cell efficiency tables (version 51). Prog. Photovolt. Res. Appl. 26, 3–12.
6. Green, M.A. (2003). General temperature dependence of solar cell performance and implications for device modelling. Prog. Photovolt. Res. Appl. 11, 333–340. 7. Peters, I.M., Liu, H., Reindl, T., and Buonassisi, T. (2018). Global Prediction of Photovoltaic Field Performance Differences Using Open-Source Satellite Data. Joule 2, 307–322. 8. Peters, I.M., and Buonassisi, T. (2018). Energy Yield Limits for Single-Junction Solar Cells. Joule 2, this issue, 1160–1170. 9. Abate, A. (2017). Perovskite Solar Cells Go Lead Free. Joule 1, 659–664. 10. Quan, L.N., Yuan, M., Comin, R., Voznyy, O., Beauregard, E.M., Hoogland, S., Buin, A., Kirmani, A.R., Zhao, K., Amassian, A., et al. (2016). Ligand-Stabilized ReducedDimensionality Perovskites. J. Am. Chem. Soc. 138, 2649–2655. 11. Anaya, M., Lozano, G., Calvo, M.E., and Mı´guez, H. (2017). ABX 3 Perovskites for Tandem Solar Cells. Joule 1, 769–793. 12. Werner, J., Niesen, B., and Ballif, C. (2018). Perovskite/Silicon Tandem Solar Cells: Marriage of Convenience or True Love Story? - An Overview. Adv. Mater. Interfaces 5, 1700731.
Preview
Taking the Positive with the Negative Rahul Malik1,* In this issue of Joule, Haoshen Zhou, Shaohua Guo, and colleagues reveal a layered transition metal oxide cathode material that can sequentially intercalate alkali cations and anions, together contributing a capacity exceeding the traditionally defined theoretical limit by more than one third. The authors demonstrate a new concept of cationic and anionic co-(de)intercalation in P3-Na0.5Ni0.25Mn0.75O2, a sodium ion cathode material with 134 mAh g 1 theoretical capacity based on complete Na extraction, but here shown to be capable of delivering 180 mAh g 1 reversible capacity (at 20 mA g 1) through the additional intercalation of anions from the electrolyte. The notion that improving battery technology is a critical driver of human prosperity is steadily gaining traction in the public consciousness, and increasingly recognized far beyond the confines of the battery research com-
munity. Not only do savvy consumers recognize that ‘‘better batteries mean better products,’’ but they also appreciate that the technology ‘‘is frustratingly slow to advance, due to both the chemical processes involved
1034 Joule 2, 1028–1038, June 20, 2018 ª 2018 Published by Elsevier Inc.
and the challenges that exist around commercializing new battery designs.’’1 Modern lithium ion batteries have proven effective at storing energy through the reversible intercalation of lithium into host crystal structures of active electrode materials—usually a graphitic carbon anode and a layered transition metal oxide cathode, respectively. The ‘‘rocking chair’’ design, based on shuttling the guest alkali species (Li) from cathode to anode upon charge, and the reverse during discharge, is the basis for powering modern portable electronics and electric vehicles.2
1Joule,
Cell Press, 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, USA *Correspondence: [email protected] https://doi.org/10.1016/j.joule.2018.06.002