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Conventionally, we expect the transport of intercalated species in battery active particles is limited by diffusion. MgCr2O4 has been identified as a candidate active material for the Mg batteries based on its theoretical Mg-storing capacity, high open circuit potential, and acceptable diffusion barrier for Mg-ion transport (1,2). However, when operated electrochemically, its performance does not match the promised potential (3). Motivated by these observations, we examine charge transport in dense MgCr2O4 pellets in an electrolyte-free setup to conclusively probe bulk Mg transport. We find that the ion transport in this material cannot be explained by using the conventional understanding. We propose a new theory that extends the conventional picture and accounts for the unusual behavior in MgCr2O4 (4). We further discuss the implications of this understanding for engineering active material particles in MgCr2O4 porous electrodes. References Canepa, P.; Sai Gautam, G.; Hannah, D. C.; Malik, R.; Liu, M.; Gallagher, K. G.; Persson, K. A.; Ceder, G. (2017) "Odyssey of Multivalent Cathode Materials: Open Questions and Future Challenges." Chem. Rev., 117 (5), 4287–4341. DOI: 10.1021/acs.chemrev.6b00614. Bayliss, R. D.; Key, B.; Sai Gautam, G.; Canepa, P.; Kwon, B. J.; Lapidus, S. H.; Dogan, F.; Adil, A. A.; Lipton, A. S.; Baker, P. J.; Ceder, G.; Vaughey, J. T.; Cabana, J. (2020) "Probing Mg Migration in Spinel Oxides." Chem. Mater., 32 (2), 663–670. DOI: 10.1021/acs.chemmater.9b02450. Hu, L.; Johnson, I. D.; Kim, S.; Nolis, G. M.; Freeland, J. W.; Yoo, H. D.; Fister, T. T.; McCafferty, L.; Ashton, T. E.; Darr, J. A.; Cabana, J. (2019) "Tailoring the Electrochemical Activity of Magnesium Chromium Oxide towards Mg Batteries through Control of Size and Crystal Structure." Nanoscale, 11 (2), 639–646. DOI: 10.1039/C8NR08347A. Johnson, I.D.; Mistry, A.; Yin, L.; Murphy, M.; Wolfman, M.; Fister, T. T.; Lapidus, S. H.; Cabana, J.; Srinivasan, V.; Ingram, B. J. (2022) "Investigating Charge Transport in MgCr2O4 Extends the Understanding of Battery Intercalation Hosts.", under review

The magnesium battery (utilizing the reversible reactivity of Mg2+) offers the potential to surpass the Li-ion battery in terms of energy-density and cost, thereby enabling next-generation devices such as lower-cost and higher-range electric vehicles.1 A crucial component defining the energy density of the Mg battery is the cathode, which must display reversible Mg intercalation and redox chemistry at sufficiently high capacities and potentials. Of all known cathode materials, the Mg spinels MgM2O4 (where M = Cr, Mn, V) have conclusively demonstrated high capacity and high potentials vs Mg2+/Mg.2–5 The spinel structure possesses 3D networks of diffusion channels, with a combination of theoretical and experimental studies suggesting relatively low barriers for Mg2+ diffusion.5,6 However, reversible Mg2+ intercalation kinetics have proven to be extremely inhibitive in oxide cathode materials in general, with large overpotentials (and voltage hysteresis) observed on charge and discharge. While the origin of this effect is still a matter of debate, it has been suggested that sluggish bulk transport of Mg2+ can partially account for the hysteresis observed, although surprisingly little is known about the nature of ion transport (both electrons and Mg2+) in these systems. In this presentation, we discuss a combination of experimental and theoretical tools used to extract key ion and electron transport properties across a range of Mg-containing spinels, Mg(Cr1−x M)2O4, where M = Mn, V, Ti. We reveal the structure-composition-property relationships that emerge across this range of compounds and discuss the relative and cooperative role that ion and electron motion play in limiting conduction kinetics in these materials. This study represents a detailed treatment of bulk ion and electron transport in these systems, and provides analytical and theoretical tools to further study electrode materials for such next-generation energy storage devices. References: (1) Canepa, P.; Sai Gautam, G.; Hannah, D. C.; Malik, R.; Liu, M.; Gallagher, K. G.; Persson, K. A.; Ceder, G. Odyssey of Multivalent Cathode Materials: Open Questions and Future Challenges. Chem. Rev. 2017, 117 (5), 4287–4341. (2) Hu, L.; Jokisaari, J. R.; Kwon, B. J.; Yin, L.; Kim, S.; Park, H.; Lapidus, S. H.; Klie, R. F.; Key, B.; Zapol, P.; Ingram, B. J.; Vaughey, J. T.; Cabana, J. High Capacity for Mg2+ Deintercalation in Spinel Vanadium Oxide Nanocrystals. ACS Energy Lett. 2020, 5 (8), 2721–2727. (3) Kwon, B. J.; Yin, L.; Park, H.; Parajuli, P.; Kumar, K.; Kim, S.; Yang, M.; Murphy, M.; Zapol, P.; Liao, C.; Fister, T. T.; Klie, R. F.; Cabana, J.; Vaughey, J. T.; Lapidus, S. H.; Key, B. High Voltage Mg-Ion Battery Cathode via a Solid Solution Cr–Mn Spinel Oxide. Chem. Mater. 2020, 32 (15), 6577–6587. (4) Kwon, B. J.; Lau, K. C.; Park, H.; Wu, Y. A.; Hawthorne, K. L.; Li, H.; Kim, S.; Bolotin, I. L.; Fister, T. T.; Zapol, P.; Klie, R. F.; Cabana, J.; Liao, C.; Lapidus, S. H.; Key, B.; Vaughey, J. T. Probing Electrochemical Mg-Ion Activity in MgCr2 − x V x O4 Spinel Oxides. Chem. Mater. 2020, 32 (3), 1162–1171. (5) Bayliss, R. D.; Key, B.; Sai Gautam, G.; Canepa, P.; Kwon, B. J.; Lapidus, S. H.; Dogan, F.; Adil, A. A.; Lipton, A. S.; Baker, P. J.; Ceder, G.; Vaughey, J. T.; Cabana, J. Probing Mg Migration in Spinel Oxides. Chem. Mater. 2020, 32 (15), 663–670. (6) Liu, M.; Rong, Z.; Malik, R.; Canepa, P.; Jain, A.; Ceder, G.; Persson, K. A.; Liu, M. Spinel Compounds as Multivalent Battery Cathodes: A Systematic Evaluation Based on Ab Initio Calculations. Energy Environ. Sci 2015, 8 (3), 964–974. Acknowledgements: The authors would like to acknowledge funding support from the Joint Center for Energy Storage Research (JCESR, a U.S. Department of Energy, Energy Innovation Hub).

Understanding and optimizing electrochemically active zone for oxygen reduction reaction in solid oxide fuel cells (SOFCs) cathodes are indispensable to maximize device’s performance. For mixed ionic and electronic conductors, the range of this zone depends on the oxygen surface exchange and solid-state oxygen/electron transport properties of materials [1]. This aspect is also critical to realize valid characterization of the electrode’s electrochemical activities. For instance, when a material’s electronic conductivity is low or the electrical contact points are spaced beyond a critical distance, the electrode polarization resistance measured by electrochemical impedance spectroscopy will be controlled by the sheet resistance not the oxygen exchange resistance [2]. The situation becomes more complicated as the electrical conductivity of porous layer, which is an advantageous structure with large surface area and facile gas phase transport, considerably deviates from the material’s intrinsic property. It is expected that porosity, connectivity, and impurity contents can have significant impact on porous electrode’s electronic conduction [3]. In this context, we have studied effective in-plane electronic conductivity of lanthanum strontium cobalt ferrite (LSCF) porous layers. The in-plane conductivity was measured by four-line probe configuration [4], modified from the widely used four-point probe technique to be applied for a porous layer. We have confirmed that the in-plane electrical conductivity of screen-printed LSCF porous layers is one or two orders of magnitude lower than the material’s bulk property in ambient air, depending on temperatures. This electronic conductivity deviation was taken into account to rationally design combination of electrode thickness and current collector spacing and, in turn, to guarantee a valid assessment of electrode performance. In addition, we found that electrical conductivity of LSCF porous layers decreases by 20~30 %, within relatively short period of time (250~400 hours) upon repeated thermal cycles (500 ℃ to 700 ℃). Furthermore, we found that in-plane conductivity of thin ( strongly dependent on the measurement time and the local atmospheric environment relative to thicker electrodes. Special attention is required to use a thin electrode to evaluate electrode performance. This work was supported by the US Department of Energy (DOE), Office of Fossil Energy, (Office of Clean Coal & Carbon Management), “Solid Oxide Fuel Cell Manufacturing in Support of Office of Fossil Energy” program through Argonne National Laboratory under FWP No. 27327.1. [1] S.B. Adler et al. J. Electrochem. Soc. 143 (1996) 3554-3564; S.B. Alder Solid State Ionics 111 (1998) 125-134. [2] B.A. Boukamp et al. Solid State Ionics 192 (2011) 404-408; B.A. Boukamp et al. Solid State Ionics 283 (2015) 81-90. [3] L. Holzer et al. J. Mater. Sci. 48 (2013) 2934-2952. [4] S.W. Peterson et al. J. Electrochem. Soc. 161 (2014) A2175-A2181.

Multivalent-ion batteries, based on the reversible reactivity of metal cations Mn+ (where n ≥ 2), offer great promise to supersede the current state-of-the-art Li-ion battery and provide a step change in energy storage capability. Oxide materials based on the spinel structure, AB2O4 (where A is the diffusing ion, M2+) have previously demonstrated potential to be high capacity, high voltage cathode materials for such batteries, with a 3D network of M2+ diffusion channels to facilitate ion transport.1–3 In particular, the MgCr2O4 spinel has been of interest due the predicted high electrochemical potential (~3.5 V) of Cr3+/Cr4+ vs. Mg/Mg2+.2 However, reversible Mg2+ intercalation kinetics has often proven to be poor in such systems, with large overpotentials observed on charge and discharge.3,4 The origin of these kinetic barriers is still poorly understood, where it is postulated that poor Mg2+ diffusion through the oxide lattice, sluggish ion transfer between the electrode and electrolyte, or resistive surface layers from electrolyte decomposition products may be responsible. In this presentation, we discuss the application of solid-state impedance spectroscopy to a library of doped spinel compounds, M1−x Cr2−2x Ti2x O4, where M = Mg or Zn, to elucidate the diffusion behavior of Mg2+ and Zn2+ in these systems. We reveal that incorporation of Ti had significant impact on the impedance behavior of the materials. As both M2+ and e− were found to diffuse in these materials, they displayed mixed ionic and electronic conductor (MIEC) behavior.5,6 This presentation includes the development and interpretation of a new physical model to describe the motion of M2+ and e− in the M1−x Cr2−2x Ti2x O4 spinel, which was necessary to accurately describe their diffusive behavior and extract their conductivities. This study therefore represents a breakthrough in the understanding of M2+ motion in these systems, and provides a methodological framework for further studies of other electrode chemistries. References: (1) Canepa, P.; Sai Gautam, G.; Hannah, D. C.; Malik, R.; Liu, M.; Gallagher, K. G.; Persson, K. A.; Ceder, G. Odyssey of Multivalent Cathode Materials: Open Questions and Future Challenges. Chem. Rev. 2017, 117 (5), 4287–4341. (2) Liu, M.; Rong, Z.; Malik, R.; Canepa, P.; Jain, A.; Ceder, G.; Persson, K. A.; Liu, M. Spinel Compounds as Multivalent Battery Cathodes: A Systematic Evaluation Based on Ab Initio Calculations. Energy Environ. Sci 2015, 8 (3), 964–974. (3) Hu, L.; Johnson, I. D.; Kim, S.; Nolis, G. M.; Freeland, J.; Yoo, H. D.; Fister, T. T.; McCafferty, L.; Ashton, T. E.; Darr, J. A.; et al. Tailoring the Electrochemical Activity of Magnesium Chromium Oxide Towards Mg Batteries Through Control of Size and Crystal Structure. Nanoscale 2019, 11, 639–646. (4) Shimokawa, K.; Ichitsubo, T. Spinel–Rocksalt Transition as a Key Cathode Reaction toward High-Energy-Density Magnesium Rechargeable Batteries. Current Opinion in Electrochemistry. Elsevier B.V. 2020, pp 93–99. (5) Lai, W.; Haile, S. M. Impedance Spectroscopy as a Tool for Chemical and Electrochemical Analysis of Mixed Conductors: A Case Study of Ceria. J. Am. Ceram. Soc. 2005, 88 (11), 2979–2997. (6) Jamnik, J.; Maier, J. Treatment of the Impedance of Mixed Conductors. Equivalent Circuit Model and Explicit Approximate Solutions. J. Electrochem. Soc. 1999, 146 (11), 4183–4188.

Multivalent (MV) ion batteries have been under intense scrutiny because the modeling effort predicted that a high Mg2+ diffusion mobility in spinel cathodes and a higher specific energy density can be achieved. Recently new cathodes have been tested against Mg, with novel cathodes such as layered oxides MoO2.8F0.2,1 MgCr2-xVxO4,2 and conversion-type cathodes.3 Previously chloride containing electrolytes4 were dominant in multivalent ion batteries because of their facile deposition and high Coulombic efficiency towards the anode. However, the corrosion issue of Cl- limits their application. Here we report the development of chloride-free multivalent salts with a weakly coordinating anion that shows exceptional electrochemical properties. Moreover, the passivation-free properties of these anions make them efficient in assessing the Mg2+ mobility inside a solid solution electrode. Further development on other multivalent cations will also be demonstrated. Together with cathodes, these electrolyte developments would pave the way for a holistic approach towards high energy density multivalent batteries. References T. Incorvati, L. F. Wan, B. Key, D. Zhou, C. Liao, L. Fuoco, M. Holland, H. Wang, D. Prendergast, K. R. Poeppelmeier, Chemistry of Materials 2015, 28, 17-20. J. Kwon, K.-C. Lau, H. Park, Y. A. Wu, K. L. Hawthorne, H. Li, S. Kim, I. L. Bolotin, T. T. Fister, P. Zapol, R. F. Klie, J. Cabana, C. Liao, S. H. Lapidus, B. Key, J. T. Vaughey, Chemistry of Materials 2019. DOI:10.1021/acs.chemmater.9b04206 Pan, J. Huang, Z. Feng, L. Zeng, M. He, L. Zhang, J. T. Vaughey, M. J. Bedzyk, P. Fenter, Z. Zhang, C. Liao, Advanced Energy Materials 2016, 6. Pan, J. Huang, N. Sa, S. M. Brombosz, J. T. Vaughey, L. Zhang, A. K. Burrell, Z. Zhang, C. Liao, * Journal of The Electrochemical Society 2016, 163, A1672-A1677. -C. Lau, T. J. Seguin, E. V. Carino, N. T. Hahn, J. G. Connell, B. J. Ingram, K. A. Persson, K. R. Zavadil, C. Liao, * J. Electrochem. Soc. 2019, 166, A1510-A1519.

The development of a Mg ion based energy storage system could provide several benefits relative to today's Li-ion batteries, such as improved energy density. The electrolytes for Mg batteries, which are typically designed to efficiently plate and strip Mg, have not yet been proven to work with high voltage cathode materials that are needed to achieve high energy density. One possibility is that these electrolytes are inherently unstable on porous electrodes. To determine if this is indeed the case, the electrochemical properties of a variety of electrolytes were tested using a porous carbon coating on graphite foil and stainless steel electrodes. It was determined that the oxidative stability limit on these porous electrodes is considerably reduced as compared to those found using polished platinum electrodes. Furthermore, the voltage stability was found to be about 3 V vs. Mg metal for the best performing electrolytes. These results imply the need for further research to improve the stability of Mg electrolytes to enable high voltage Mg batteries.

NiO-GDC, NiO-YSZ, NiO-Fe2O3-GDC, NiO-Fe2O3-YSZ anode tube supported tubular fuel cells was fabricated at the co-sintering temperature from 1250 oC to 1400 oC to investigate how the co-sintering temperature affect the open-circuit voltage. To focus on the changing of anode tube, all the tubular fuel cells support a ScSZ electrolyte layer and a LSCF cathode layer. The microstructure of the electrolyte layer sintered under 1300 oC included pores inside it, and the densification of the electrolyte completed at the sintering temperatures above 1300 oC. Furthermore, the shrinkage both in length and in diameter of a tubular fuel cell reaches as much as 20% at co-sintering temperature of 1400 oC. The densification of ScSZ electrolyte layer and shrinkage of anode tube will result in the changing of open-circuit voltage of fuel cell from 1.0 V to 1.1 V.

In the search for future beyond-Li-ion batteries, Mg batteries present a safe option due to lower pyrophoricity and no formation of dendrites during electrodeposition and dissolution. However, the practical voltage window of Mg batteries is limited by the paucity of both cathodically and anodically stable electrolytes. Recently, carborane,1,2 fluoroalkoxyaluminate3 and fluoroalkoxyborate-based4 electrolytes emerged as potential candidates for high-voltage Mg electrolytes. Inspired by the latter work, we demonstrate in this presentation that magnesium perfluoroalkoxyaluminate as a Mg electrolyte can be rationally designed and synthesized to exhibit unprecedented anodic stability while retaining the capability of Mg electrodeposition and dissolution. Synthesis, spectroscopic characterization and electrochemistry of the electrolyte will be discussed. Tutusaus, R. Mohtadi, T. S. Arthur, F. Mizuno, E. G. Nelson and Y. V. Sevryugina, Angew. Chem. Int. Ed. 54, 7900 (2015). G. McArthur, L. Geng, J. Guo and V. Lavallo, Inorg. Chem. Front. 2, 1101 (2015). T. Herb, C. A. Nist-Lund and C. B. Arnold, ACS Energy Lett. 1, 1227 (2016). Zhao-Karger, M. E. G. Bardaji, O. Fuhr and M. Fichtner, J. Mater. Chem. A 5, 10815 (2017).

With solid oxide fuel cells operating at 800{degree sign}C or lower, metal alloy bipolar plates (interconnects) offer a number of advantages over ceramic interconnects. However, these alloys rely on the formation of a protective chromium based scale, either chromia or a manganese chromium spinel. As metallic bipolar plates have been explored, and used, over the last decade, a number of interactions have been observed between the bipolar plate and various cathode materials. This paper examines the interactions between E-Brite® and an LSM/YSZ composite active cathode. Tests examined direct contact of the E-Brite® with the cathode, and the effect of using gold foil as a physical barrier so only gas phase interactions were possible. Additionally, key observations on test fixture design and materials selection are discussed, which may shed light on why different researchers have observed a wide range of fuel cell degradation rates.

Recently, new energy storage chemistries based on nonaqueous electrolytes and multivalent metals (e.g., Mg, Zn, Ca and Al) have drawn the attention of the researchers as a promising advanced energy storage technology due to their higher theoretical volumetric capacity, limited dendrite formation and low cost.1 A major developmental need for these systems is the identification of electrolytes compatible with both electrodes while showing reversible deposition/dissolution on an anode and multivalent intercalation into a cathode.1,2 In the case of nonaqueous Mg or Ca ion-based systems, electrolyte compatibility issues (e.g., low Coulombic efficiency, a high overpotential and corrosion) have held back the development of Mg or Ca metal batteries.3 However, the nonaqueous Zn2+ ion chemistry utilized in a Zn metal cells with a reversible intercalation cathode is an exception with a number of promising features including highly-efficient reversible Zn deposition/dissolution on a Zn metal anode with a wide electrochemical window,3 similar ionic radius compared with Li+ and Mg2+ ions,4 relatively lower activation barrier energy for diffusion in cathode materials (e.g., FePO4, CoO2 and V2O5)5 and high volumetric capacity.1 Considering these advantages, a nonaqueous Zn system provides an opportunity to delve into the mechanisms in multivalent-ion cell chemistry and solve the present issues in multivalent cell design and prototyping.3 In this study, the intercalation chemistry on a variety of cathodes materials (e.g., V2O5, Mn2O4 and FePO4) have been investigated in various nonaqueous Zn electrolytes. The electrochemical and transport properties of the electrolytes (e.g., reversible Zn deposition, anodic/cathodic stability, ionic conductivity and diffusion coefficient) were characterized utilizing the experimental and computational analysis.3 Among various Zn metal cells, a Zn/nanostructured bilayered V2O5 cell with a selected acetonitrile(AN)-Zn(TFSI)2 electrolyte demonstrates good reversibility and stability for 120+ cycles with nearly 100% Coulombic efficiency and ~170 mAhg-1 of gravimetric capacity, albeit operating at a cell voltage of 0.7 V vs. Zn/Zn2+.6 A Zn/nanostructured layered δ-MnO2 cell with an AN-Zn(TFSI)2 electrolyte also shows good reversibility (~100% Coulombic efficiency) and stability for 50+ cycles with ~100 mAhg-1 capacity with an operating voltage of 1.2 V vs. Zn/Zn2+.7 By utilizing a combination of analytical tools, we address numerous factors affecting capacity fade, and issues associated with the second phase formation including Mn dissolution in Zn/δ-MnO2 cells that have been extensively cycled.7 References 1. J. Muldoon, C. B. Bucur and T. Gregory, Chem. Rev. 2014, 114, 11683-11720. 2. H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour and D. Aurbach, Energy Environ. Sci. 2013, 6, 2265-2279. 3. S.-D. Han, N. N. Rajput, X. Qu, B. Pan, M. He, M. S. Ferrandon, C. Liao, K. A. Persson and A. K. Burrell, ACS Appl. Mater. Inter. 2016, 8, 3021-3031. 4. R. D. Shannon, Acta Cryst. 1976, A32, 751-767. 5. Z. Rong, R. Malik, P. Canepa, G. Gautam, M. Liu, A. Jain, K. Persson and G. Ceder, Chem. Mater. 2015, 27, 6016-6021. 6. P. Senguttuvan, S.-D. Han, S. Kim, A. L. Lipson, S. Tepavcevic, T. T. Fister, I. D. Bloom, A. K. Burrell and C. S. Johnson, Adv. Energy Mater. 2016, 6, 1600826. 7. S.-D. Han, S. Kim, D. Li, V. Petkov, H. D. Yoo, P. J. Phillips, H. Wang, J. J. Kim, K. L. More, B. Key, R. F. Klie, J. Cabana, V. Stamenkovic, T. T. Fister, N. M. Markovic, A. K. Burrell, S. Tepavcevic, J. T. Vaughey, 2017, in revision.

Lithium-ion batteries have been a mainstay of the consumer electronics industries for nearly 25 years. Unlike many older energy storage systems, lithium-ion does not describe a specific chemistry but a family of chemistries and a mechanism of operation. As a result numerous types of materials are under the umbrella of lithium-ion batteries that can be modified and developed to meet a variety of end-user goals. Looking beyond-lithium ion, the landscape is less understood and explored. One of our research efforts is to look at non-lithium cation based energy storage chemistries, including the MgxV2O5 and MgxV2O5*H2O systems. This talk will focus on recent developments from our lab in Mg-ion and Ca-ion chemistries with highlighting new types of cathodes, electrolytes, and anode materials1-5 References (1) Lipson, A.L; Han, S.-D; Kim, S. Pan, BF; Sa, N.; Liao; C, Fister, TT; Burrell, AK; Vaughey, JT; Ingram, BJ J. Power Sources 325 646-652 (2016). (2) Sa, N; Wang, H; Proffit, DL; Lipson, AL; Key, B; Liu, M; Feng, ZX; Fister, TT; Ren, Y; Sun, CJ; Vaughey, JT; Fenter, PA; Persson, KA; Burrell, AK J. Power Sources 323 44-50 (2016). (3) Sa, N; Kinnibrugh, TL; Wang, H; Gautam, GS; Chapman, KW; Vaughey, JT; Key, B; Fister, TT; Freeland, JW; Proffit, DL; Chupas, PJ; Ceder, G; Bareno, JG; Bloom, ID; Burrell, AK Chemistry of Materials, 28(9) 2962-2969 (2016). (4) Lipson, AL; Han, SD; Pan, B; See, KA; Gewirth, AA; Liao; Vaughey, J; Ingram, BJ J. Electrochem. Soc., 163(10) A2253-A2257 (2016). (5) Mukherjee, A.; Sa, N.; Phillips, P.; Burrell, AK; Vaughey, JT; Klie, R. Chemistry of Materials, 29, 2218−2226 (2017). Figure 1

For applications involving transportation and the electricity grid, future energy storage systems will require high energy density, fast charge/discharge times, increased safety, and low cost compared to current Li-ion batteries. Non-aqueous multivalent metal (Mg, Zn, Ca, Al) based cells are a promising advanced energy storage technology due to their higher theoretical volumetric capacity, limited dendrite formation, and low cost. A major need for these systems is the development of compatible electrolytes for both electrodes that show reversible multivalent intercalation cathodes.1,2 In the case of non-aqueous Mg or Ca ion systems the electrolyte compatibility issues (e.g., low Coulombic efficiency, a high overpotential, and corrosion) hold back the development of Mg or Ca metal batteries.3 However, non-aqueous Zn2+ ion chemistry in Zn metal cells with a reversible intercalation cathode is an exception among multivalent metals with a number of promising features including high volumetric capacity,1 similar ionic radius compared with Li+ and Mg2+ ions,4 relatively lower activation barrier energy for diffusion in cathode materials (e.g., FePO4, CoO2 and V2O5)5 and highly-efficient reversible Zn deposition behavior on a Zn metal anode with wide electrochemical window.3 Considering these advantages, a non-aqueous Zn system provides an opportunity to delve into the mechanisms in multivalent-ion cell chemistry and solve the present issues in multivalent cell design and prototyping.3 In this study, the intercalation chemistry on a variety of cathodes materials (e.g., V2O5 and Mn2O4) and reversible deposition/dendritic growth issues on a Zn metal anode have been investigated in various non-aqueous Zn electrolytes. The electrochemical and transport properties―reversible Zn deposition behavior, Coulombic efficiency, anodic stability, ionic conductivity and diffusion coefficient―were characterized utilizing the experimental and computational analysis. Among various Zn metal cells, a hydrated Zn/nanostructured bilayered V2O5 cell with an acetonitrile(AN)-Zn(TFSI)2 electrolyte demonstrates good reversibility and stability for 120+ cycles with nearly 100% Coulombic efficiency and ~170 mAhg-1 of gravimetric capacity, albeit operating at a cell voltage of 0.7 V.6 A low crystalline Zn/Nanostructured δ-MnO2 cell with an AN-Zn(TFSI)2 electrolyte also shows good reversibility (~100% Coulombic efficiency) and stability for 50+ cycles with ~100 mAhg-1 capacity and relatively higher operating voltage of 1.2 V. On the other hand, Zn dendrite growth studies on a Zn metal anode in non-aqueous Zn electrolytes have been performed under various conditions, including various current densities (0.1, 1.0, and 10 mA cm-2) and time (0.2 and 2.0 h cycle-1). The cycled Zn metal anodes were characterized using SEM-EDX and X-ray tomography to analyze morphological changes and dendritic growth in both selected regions and overall samples. References J. Muldoon, C. B. Bucur and T. Gregory, Chem. Rev. 2014, 114, 11683-11720. H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour and D. Aurbach, Energy Environ. Sci. 2013, 6, 2265-2279. S.-D. Han, N. N. Rajput, X. Qu, B. Pan, M. He, M. S. Ferrandon, C. Liao, K. A. Persson and A. K. Burrell, ACS Appl. Mater. Inter. 2016, 8, 3021-3031. R. D. Shannon, Acta Cryst. 1976, A32, 751-767. Z. Rong, R. Malik, P. Canepa, G. Gautam, M. Liu, A. Jain, K. Persson and G. Ceder, Chem. Mater. 2015, 27, 6016-6021. P. Senguttuvan, S.-D. Han, S. Kim, A. L. Lipson, S. Tepavcevic, T. T. Fister, A. K. Burrell and C. S. Johnson, 2016, submitted.

Since it was first introduced by Abraham and Jiang, the nonaqueous rechargeable Li-O2 battery has recently attracted considerable attention as a possible energy storage device for electric vehicle (EV) application owing to its extremely high theoretical energy density, which far exceeds that of any other existing energy storage technologies. The theoretical specific energy of a non-aqueous Li-O2 cell is approximately 11 kWh/kg, which approaches that of the gasoline, if the calculation is based on the lithium electrode alone. A typical non-aqueous Li-O2 cell, which consists of a Li anode, Li+ conducting aprotic electrolyte and porous carbon cathode, operates by reduction of O2 to form lithium oxides within the pores of the cathode during discharge, with the process being reversed on charge ideally. It is based on the net electrochemical reaction (1) with a thermodynamic potential U1 = 2.96 V, from the Nernst equation. 2Li+ + 2e- + O2 Li2O2 (1) Early experiments exhibited very high charge overpotenials (>1V) for Li-O2 cells, mostly in the carbonate-based electrolytes (e.g. LiPF6 in propylene carbonate), which result in large energy storage inefficiency. Although considerable electrolytic reduction of charging overpotential can be achieved when metal or metal oxide nanoparticles are incorporated into the porous carbon cathode, the carbonate or mixed ether-carbonate based electrolytes are known to severely decompose on cell discharge. Such decomposition leads to the discharged product consisting of a mixture of lithium propyl dicarbonate, lithium carbonate, HCO2Li, CO2, C3H6(OCO2Li)2, CH3CO2Li etc., rather than the desired lithium peroxide, Li2O2. Subsequent charging involved the partial decomposition of these Li-containing compounds with CO2 and H2O evolution, which correlated with high charge overpotential and capacity fading alongside electrolyte consumption. Considering the scientific and technological significance, it is important to understand the underpinning mechanisms and identify the products in the process of charging lithium oxides cathode in a Li-O2 cell. The goal of this work is to experimentally determine the reactions involved in charging Li-O2 cathodes in different electrolytes, i.e. propylene carbonate (PC), tri(ethylene glycol)-substituted methyltrimethyl silane (1NM3) and Tetraethylene glycol dimethyl ether (TEGDME) with a Li containing salt. Several techniques were carried out to demonstrate electrochemical decomposition of lithium oxides and other side reactions involved, including in-situ high-energy X-ray diffraction (HE-XRD), X-ray photoelectron spectroscopy (XPS) and gaschromatography (GC). Figure 1 emphasizes the importance of salt selection on the performance. Based on previous reports, the decomposition of lithium salts used in the electrolytes could cause the detrimental electrolyte decomposition in Li–O2 batteries. Therefore, the electrolyte decomposition may be responsible for increasing the charge capacities.. To further confirm that lithium oxides can be electrochemically decomposed, in situ X-ray diffraction patterns during the charge process of Li2O2 in LiTFSI +1NM3 electrolyte were collected and displayed in figures 2 which clearly shows that the Li2O2 peaks totally disappeared during the charge process to 2750 mAh·g-1. The peaks of Li are also confirmed by XPS analysis, and its intensity was enhanced gradually during charging. So we can preliminarily estimate that the Li2O2 does decompose to Li and O2. More importantly, there were no other peaks appearing, especially for LiF, which means that there are no side reactions for the (LiTFSI + 1NM3) electrolyte. Therefore, it is of critically important to confirm that the recorded performance was indeed a measure of the electrochemical decomposition of Li2O2. Interestingly, for the charge capacity of 2750 mAh·g−1 obtained using LiTFSI+1NM3, the Li2O2 had totally decomposed electrochemically, as shown in figure 2. Hence, it’s further confirmation that the side reactions from electrolyte decomposition are responsible for the capacity increase shown in figure 1. Figure 1

Batteries based on magnesium or calcium metal anodes have the potential to achieve energy densities exceeding current Li-ion batteries. However, there are major challenges to overcome to make such a battery a reality. One challenge is that currently no cathode materials have been identified that have sufficient energy density for a practical magnesium or calcium based battery. Towards the end of finding higher energy density cathode materials, this poster presents two different materials approaches for the successful incorporation of Mg and Ca. In particular, materials based on a Prussian blue type structure and with a polyanionic layered structure will be discussed. Results presented include cycling performance, X-ray diffraction and X-ray based spectroscopies that prove intercalation of both Mg and Ca. Comparing these classes of materials to others that have been shown to successfully intercalate Mg, yields insights into what makes a material a good candidate for future multivalent cathode research. With these design principles guiding the search, a material that can achieve high energy densities for Mg or Ca chemistry can hopefully be found.

Cheaper batteries with higher capacity would increase the market penetration of electric vehicles and grid storage systems. One way to achieve these gains in battery performance is to utilize a metal anode such as lithium, magnesium or calcium. Lithium metal anodes have been extensively studied for decades, but still have not been commercialized. On the other hand, comparatively little research has been performed on magnesium or calcium systems. Magnesium metal has been shown to be less susceptible to the formation of dendrites than lithium. No one is yet able to plate and strip calcium, however, it does possess a lower voltage than magnesium and a non-passivating oxide. In order to rapidly explore the potential of these battery systems, we have developed techniques to study cathode materials without the need for a working metal anode. In doing this we have determined that corrosion issues are more severe in these electrolytes than their lithium counterparts. Furthermore, we have determined a class of materials that can intercalate Mg and Ca in nonaqueous electrolytes. These materials are characterized by a combination of techniques including energy dispersive X-ray spectroscopy (EDX), X-ray absorption near-edge spectroscopy (XANES) and X-ray diffraction (XRD) to prove intercalation of the multivalent ion. Additionally, we have made the first attempts to pair these materials with low voltage anode materials. These anode materials include using Mg metal and metallic anodes that react with the multivalent ion.

We demonstrate the feasibility of using Ultra Small Angle X-ray scattering to study cathode structures in solid oxide fuel cells (SOFC) under operating conditions. Cathode thickness has been optimized and symmetric SOFC test structures have been characterized. We also demonstrate that we can follow the evolution of microstructure on a La0.6Sr0.4Co0.2Fe0.8 infiltrated yttria stablized zirconia backbone structure under annealing, showing the viability of characterizing multi-scale cathode structures in real time.

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Transmission electron microscopy was used to investigate the local chemistry and microstructure of the active cathodes in solid oxide fuel cells operated for 500 h (at 700 and 800 degrees C) under different electrochemical conditions while exposed to a chromia-forming stainless steel. Several distinct microstructural changes were observed owing to chromium interactions with the (La,Sr)MnO3 (LSM)-yttria stabilized zirconia (YSZ) cathode; the nature and magnitude of which depended on the temperature, electrochemical load, and physical location. Nanosized particles of (Cr,Mn)(3)O-4 and Cr2O3 were observed on the surface of the YSZ, regardless of the overall extent of degradation; the quantity increased with decreasing temperature and increasing current. The results indicate that Mn species facilitate the formation of a stable Cr-Mn-O nuclei on the YSZ, on which further growth occurs, including growth of Cr2O3. In cases of severe performance degradation, LSM decomposes completely, which does not appear to be strongly correlated with the nanoparticles on the YSZ, but results from a more destructive mechanism. Following this decomposition, severe pore filling of Cr-containing species occurs. The amount of microstructural degradation was largest near the cathode/electrolyte interface directly beneath the interconnect-cathode contact channels. These results indicate that two distinct mechanisms of degradation occur, with the electrochemical decomposition of (La,Sr)MnO3 as the primary cause for severe performance degradation. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3515073] All rights reserved.

Hexavalent chromium species like the oxyhydroxide, CrO{sub 2}(OH){sub 2}, or hexoxide, CrO{sub 3}, are electrochemically reduced to Cr{sub 2}O{sub 3} in solid oxide fuel cells and adversely affect the cell operating potentials. Using a narrowly focused beam from the Advanced Photon Source, such chromium oxide deposits were unequivocally identified in the active region of the cathode by X-ray diffraction, suggesting that the triple phase boundaries were partially blocked. Under fuel cell operating conditions, the reaction has an equilibrium potential of about 0.9 V and the rate of chromium oxide deposition is therefore dependent on the operating potential of the cell. It becomes diffusion limited after several hours of steady operation. At low operating potentials, lanthanum manganite cathodes begin to be reduced to MnO, which reacts with the chromium oxide to form the MnCr{sub 2}O{sub 4} spinel.

Chromium transport from stainless steel current collectors to the cathode can be a route for rapid performance degradation in solid oxide fuel cells. Typical volatile chromium species, such as CrC 2 (OH) 2 , are manageable; however, volatile species with higher vapor pressures may play a significant role in chromium transport and deposition. One such species, K 2 CrO 4 , is readily formed by the chemical reaction between KOH or K 2 O and Cr 2 O 3 and electrochemically reduced along triple-phase boundaries. The vapor pressure and expected chromium deposition rate of potassium chromate and chromium oxyhydroxide phases are compared to the long-term electrical performance of anode-supported SOFCs. Experimental evidence supports the findings that potassium and chromium, in the presence of an applied electric field, greatly enhances the degradation of cell performance (-85% in 500 h).

A method for measuring the conductivity of ceramic powders has been developed using effective medium theory and impedance spectroscopy. Powders to be tested are mixed with aqueous solutions of varying NaCI concentrations to form a composite slurry. The impedance response of these powder-solution-composites (PSCs) is measured and analyzed using composite equivalent circuit and effective medium theories. Values obtained for a test powder of copper aluminate (CuAlO 2 ) match closely to four-point dc values measured on bulk sintered bars. A comparison was also made in a system with highly composition-dependent conductivity (YITO, In 2-2x-2y Y 2x Sn 2y O 3 , 0.08 ≤ x ≤ 0.20) to evaluate the upper and lower bounds for accurate measurements. Results from the PSC method matched the sintered bar four-point dc values within the range of NaCI solutions employed (0.5-10 -4 S/cm).