The development of advanced materials and technologies to efficiently convert and store energy directly into electricity is of urgent importance due to increasing energy demands of an ever growing world population and decreasing energy reserves. However tremendous scientific challenges remain before successful implementation of any number of competing energy technologies such as solar cells, fuel cells, and batteries. The materials, interfaces and device architectures currently being explored are very challenging to interrogate by ensemble-averaging, bulk experimental methods since they do not exhibit long-range order or homogeneity, contain unique nano-morphological features and possess non-uniform chemical compositions and defect chemistry. This presentation will summarize a few materials design strategies for optimizing the performance of redox-active materials for use in electrochemical energy storage applications and highlight the development of high resolution experimental and theoretical tools for studying charge transfer processes at electrode interfaces. Information obtained from these studies provides fundamental understanding of electron and ion transfer processes and degradation mechanisms for materials utilized for electrochemical energy storage.

Structures, Devices, and Architectures for Nanoscale Solutions in Electrical Energy Storage
G.W. Rubloff
Nano science and technology promise enhancement to batteries and capacitors through higher power at given energy, accompanied by new possibilities for better capacity retention and safety. Among the challenges to realize this promise are (1) the design of higher performance electrode and electrolyte materials and (2) the rational design of structures in which these materials are arranged. We have focused on the latter, seeking to understand how the structure of components and the architecture in which they are arranged determine the multifunctionality required for electrical energy storage: ion transport and storage, electron transport, and structural stability during charge/discharge cycling.
Precision multistep synthesis has enabled the creation of heterogeneous nanostructures, involving multiple materials to confer the needed multifunctionality and to understand how design influences electrochemical behavior at the nanoscale and storage performance of nanostructures. This is illustrated by several such structures which address fundamental phenomena important at the nanoscale and the mesoscale, including: (1) Si nanowire and nanotube structures with integrated electron transport components that achieve robust Li cycling despite large volume changes; (2) nanopore battery configurations to assess fundamental limits on ion transport in highly confined environments; (3) solid state electrolyte and battery configurations for scaling safe materials to the nanoscale; and (4) 3D nanostructure forests, both regular and pseudo-random, to analyze mesoscale architectures and new scientific challenges emerging at the mesoscale. These experimental advances have been accompanied by significant modeling and simulation insights, from DFT to continuum levels, and at the same time they pose formidable, important challenges for theory, particularly at the mesoscale.
This work has been supported by Nanostructures for Electrical Energy Storage (NEES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award Number DESC0001160.

The primary goal of the FIRST Center is to develop fundamental understanding and validated, predictive models of the unique nanoscale environment at fluid-solid interfaces that enable transformative advances in electrical energy storage and catalysis for energy. A signficant portion of our research has focussed on capacitive energy storage by ion attraction to charged interfaces, often termed electrical double layer capacitance. This type of electrical energy storage, which does not involve phase changes, redox reactions or ion intercalation into crystal lattices, frequently results in very long cycle lives and very hgh power densities, but lower energy densities than can be achieved by converting electrical to chemical energy in a battery. We have extensively explored the role of pore size versus ion size, nanoscale surface curvature and pore geometries in maximizing both power and energy density of capacitive and pseudocapacitive electrical energy storage, particularly involving room temperature ionic liquid electroltyes and nanotextured carbon electrode materials.

Energy storage represents an opportunity and a challenge for basic research to cross the technological boundaries in bringing energy independence to the U.S. Since its inception in 2009, the overriding mission of the Center for Electrical Energy Storage (CEES) has been to advance the fundamental understanding of electrochemical phenomena and the design of new materials architectures, using lithium-ion battery chemistries as a guide, for the discovery of a new generation of electrical energy storage systems.
This presentation will discuss the journey of CEES over the past 5 years. Highlights will include 1) approaches to design new anode and cathode materials and architectures, 2) the development of characterization techniques to monitor electrochemical processes at the electrode/electrolyte interface, 3) the use of autonomous chemistries to enable self-repair and shutdown reactions, and 4) theoretical approaches to complement experimental observations and discoveries.
Acknowledgments
This work was supported by the Center for Electrical Energy Storage, an Energy Frontier Research Center funded by the Office of Science, Office of Basic Energy Sciences of the U.S. Department of Energy.

This presentation will deal with the development of operando methods for the study and characterization of battery materials. The presentation will begin with a brief overview of the methods employed. Particular emphasis will be placed on the use of X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS), differential electrochemical mass spectrometry (DEMS) and transmission electron microscopy (TEM) under active potential control. The utility of these methods will be illustrated by selected examples including conversion reactions of Mn3O4 as anode material for lithium ion batteries (LIBs), spectroscopic studies of Li/S batteries and the use of DEMS to characterize electrolyte systems for LIBs. The use of operando TEM will be illustrated by studies of lithiation/de-lithiation dynamics of LiFePO4 via energy-filtered TEM. The presentation will conclude with an assessment of future directions.

The Northeastern Center for Chemical Energy Storage (NECCES) has leaded a synergistic effort in the past five years on basic research in the design of the next generation of lithium-ion batteries. The Center has enabled both the development of new chemistries and the fundamental understanding of the physical and chemical processes that occur in intercalation materials such as LiFePO4 and conversion materials such as FeF3/FeF2. The NECCES team has identified the key atomic-scale processes that govern electrode function in rechargeable batteries, over a wide range of time and length scales, via the development and use of novel characterization and theoretical tools, including in situ X-ray scattering, in situ TEM observation, in situ NMR spectroscopy and new computation/simulation tools. The information and knowledge gained are critical to identify and design new battery systems with improved electrochemical properties.

The Joint Center for Energy Storage Research combines discovery science, battery design, research prototyping and manufacturing collaboration in a single highly interactive organization to pursue transformational next generation energy storage beyond lithium ion batteries. JCESR will leave three legacies:
- a library of fundamental knowledge of the materials and phenomena of energy storage at the atomic and molecular level
-two prototypes, one for the grid and one for transportation, that, when scaled to manufacturing will be able to deliver five times the energy density at one-fifth the cost
-a new paradigm for battery R&D that accelerates the pace of discovery and innovation and significantly shortens the time from discovery to commercialization.
An introduction to JCESR&’s vision, mission and legacies will be followed by research highlights illustrating its advances in fundamental science and the promising pathways to transformational battery designs and prototypes.
This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences
Contact information
George Crabtree
Director, Joint Center for Energy Storage Research (JCESR)
Argonne National Laboratory
9700 S. Cass Ave
Argonne, IL 60439
630 252 5509
crabtree@anl.gov
Departments of Physics, Electrical and Mechanical Engineering
University of Illinois at Chicago
845 W. Taylor St. M/C 273
Chicago, IL 60607
Tel 630 252 5509
crabtree@uic.edu
Executive Assistant
Bernadette (Nada) Petrovic
Joint Center for Energy Storage Research (JCESR)
Argonne National Laboratory
9700 S. Cass Ave
Argonne, IL 60439
(630) 252-1420
bpetrovic@anl.gov

Intercalation electrodes provide the highest energy density battery systems. Hence, understanding diffusion of ions other than Li in such electrode materials is important to assess the feasibility of “Beyond Li” technologies. Both Na and Mg are being considered as alternatives to lithium. In this presentation we will compare the diffusion mechanisms for Li, Na and Mg in typical intercalation materials. Layered Na-oxides have recently been shown to be able to achieve rates > 30C, and in many layered oxides Na diffusion seems faster than Li diffusion. Mg being a divalent ion shows much slower diffusion in many intercalation hosts. Results for the migration barrier of Mg diffusion in different hosts will be shown.

The extraction, exchange, and separation of ions in solution have been studied extensively because of applications in seawater desalination, elemental purification, and wastewater treatment. Reversible electrochemical insertion of ions into materials would present a valuable alternative to existing methods of ion exchange because of the ease of cycling and reuse. Reversible insertion of monovalent ions has been thoroughly explored because of its application in intercalation battery electrodes, including electrodes for nickel-metal hydride and lithium-ion batteries. However, the stable and reversible insertion of divalent or trivalent ions into materials remains an unsolved problem.
Copper hexacyanoferrate (CuHCF), a Prussian Blue analogue, possesses a unique open framework structure that allows for the reversible insertion of a wide variety of multivalent cations, including many alkaline earth, rare earth, and transition metal cations. The material demonstrates unprecedented kinetics, reversibility, and cycle life for multivalent ion insertion. However, little is known about the processes by which multivalent ions can readily insert into CuHCF. Ongoing synchrotron X-ray and neutron diffraction experiments have begun to provide insight on the ion insertion mechanism in the material and on the complex interplay between vacancies, water molecules, and insertion ions in the structure.

Cubic garnet of nominal composition Li7La3Zr2O12 (LLZO) is of interest as a possible electrolyte in batteries composed of molten Li as an anode and sulfur or an insoluble metal halide as a cathode operating in the temperature range 300-350C. As a consequence the chemical stability of dense (>98% relative density) cubic LLZO stabilized by different dopants in molten lithium and sulfur in the temperature range 300-350C was characterized by x-ray diffraction, electron microscopy, x-ray photoemission spectroscopy and electron paramagnetic resonance. The results revealed LLZO had undergone chemical coloration and exhibited intergranular cracking after immersion in molten Li. These results will discussed and compared to other Li and Na-ion conductors tested in a similar temperature range.

Recently a new, large family of two-dimensional (2D) early transition metal carbides and carbonitrides, called MXenes, was discovered. MXenes are produced by selective etching of the A element from the MAX phases. the latter metallically conductive layered solids, connected by strong metallic, ionic, and covalent bonds such as Ti2AlC, Ti3AlC2, Ta4AlC3, etc. MXenes combine the metallic conductivity of transition metal carbide layers with the hydrophilic nature of their hydroxyl or oxygen terminated surfaces. In essence, they behave as “conductive clays”. MXenes are expected to be good candidates for a host of applications. They have already shown promising performance in electrochemical energy storage systems. However, we are only starting to explore the potential of MXenes as anode materials for Li-ion batteries and their use in electrochemical capacitors.
Herein, we report on the intercalation of Li+, Na+, Mg2+, K+, NH4+, and Al3+ ions between the 2D Ti3C2Tx and Ti2CTx layers. In most cases, the cations intercalated spontaneously. The intercalation of some ions, notably Al3+, can be promoted electrochemically. We also report on intercalation-induced high volumetric capacitance of flexible Ti3C2Tx paper electrodes. This study provides a basis for exploring a large family of 2D carbides and carbonitrides in electrochemical energy storage applications using single- and multivalent ions.

Electrochemical energy storage relies on the breaking and reforming of chemical bonds to store and recover energy. Energy is stored through the decomposition of a stable compound, MX, into more elemental components, M and X and is recovered by the reverse reaction, M+X→MX. Experience with Li-ion batteries has shown that reversibly forming and breaking bonds electrochemically is most facile for intercalation reactions, whereby ions are shuttled between electrodes and fill the interstitial sites of a rigid host structure that undergoes minimal dimensional and structural changes. First-principles computational methods have proven invaluable in elucidating and predicting a wide variety of thermodynamic and kinetic properties of electrode and electrolyte materials. In this talk I will describe how these tools can be used to explore and design new electrochemical energy storage concepts and devices.

Doped cubic phases of garnet-related Li7La3Zr2O12 (LLZ) have a strong application potential as solid electrolytes for all-solid-state batteries and as protective layers for anodes in Lithium-air batteries due to their favorable combination of high ionic conductivity with chemical and electrochemical stability versus both lithium and cathode materials. Lithium oxide volatility at temperatures suitable for conventional sintering however favors the formation of non-Li+-conducting La2Zr2O7 phase and impedes the formation of dense, phase pure membranes. Hence a lower synthesis temperature is required for the retention of Li. From Rietveld refinement of in situ neutron diffraction data in combination with thermogravimetric analysis we could determine (both the undoped and doped) LLZ variation in the mass fractions of the phases involved at different temperatures during the formation process from ball-milled precursor mixtures. Pentavalent doping on the Zr site and (to a lesser extent) trivalent doping on the Li+ sites enhance Li+ diffusion, whereas Ga3+ doping essentially stabilizes the cubic phase with minimal effect on the conductivity. Addition of 1 - 2 wt% Ga2O3 as a sintering agent to precursor mixtures for pentavalently doped LLZ has been found to densify the membrane (96% of theoretical density) at a sintering temperature of 1150°C and thus enhance the total Li+ ion conductivity by one order of magnitude. The low melting temperature of TeO2 (733°C) makes it attractive as a sintering agent. Indeed Te-doping is found to stabilize the fast ion conducting cubic phase at a moderate formation temperature of 750°C. However, the lower redox stability of Te4+ may limit application of LLZ with high Te dopant concentrations.
Low-temperature sol-gel synthesis of undoped and (Ta-, Nb- and Al-) doped LLZ samples has also been carried out. The fast ion conducting cubic phase was successfully formed at 750°C, 850°C and 950°C. La2Zr2O7 impurities in samples prepared at the lowest temperature could be suppressed by enriching the mother powder in Li2CO3 during the subsequent sintering at 900°C. Due to the porosity of the samples formed by sol-gel method the Li+ ion conductivity of the LLZ samples made was one order of magnitude lower than those made via conventional solid state reaction. Performance studies of the different LLZ samples as solid electrolytes in all-solid state batteries and as anode-protecting membrane in Li-air as well as Li redox flow battery configurations will be discussed.

Large-scale applications of lithium ion batteries for transportation and storage of renewable energy require high energy densities, high power, reduced costs and, most importantly, safety. The use of liquid organic electrolytes that exhibit high vapor pressures and flammability poses a substantial safety issue in particular for large-scale systems. Solid electrolytes offer a potential solution due to their inherent chemical stability. In addition to being lithium ion conductors, solid electrolytes act as separators between the electrodes. Recently, several material systems such as LLZO (Li₇La₃Zr₂O₁₂) have been identified that exhibit ionic conductivities similar to those of liquid electrolytes at moderate temperatures paving the way to integrate these materials in battery cells.
In the present work, we report on the synthesis and characterization of Al-doped LLZO solid electrolyte with grain sizes in the range of 40 to 300 nm. The main goal is to establish the role of the grain size and the residual porosity in the electrolyte layer on the conductivity. The material was synthesized using nebulized spray pyrolysis (NSP). NSP is an aerosol-based synthesis method that allows for a high production rate on a laboratory scale and is scalable for mass production. Pellets consolidated from as-synthesized powders were sintered at 1000 °C to obtain the desired phase-pure cubic garnet material. The structure of the powders and the sintered ceramics was characterized by means of X-Ray diffraction (XRD). Furthermore, the microstructure was analyzed using secondary electron microscopy (SEM). The electrochemical performance of the sintered pellets was studied, in relation with the microstructural information, and compared to the performance of materials prepared by solid state reaction.

The lithium solid-state electrolyte (SSE) of Li5La3Nb2O12 (LLNO) was synthesized via a novel molten salt synthesis (MSS) method at a relatively low temperature of 900°C. The low sintering temperature prevented the loss of lithium which commonly occurs during synthesis of the SSE using conventional solid-state or wet chemical reactions. Recent publications have demonstrated that preserving the Li content is critical in improving the ionic conductivity of SSEs. In this study, X-ray photoelectron spectroscopy (XPS) showed that the synthesis of the LLNO was successful, without any Li loss, by using the MSS method. The LLNO in this experiment showed a high Li-ion conductivity comparable to the values reported for LLNO in the literature. X-ray diffraction (XRD) measurements confirmed the formation of the cubic garnet Ia-3d crystal structure. In addition, the morphology was examined by scanning electron microscope (SEM), which showed a uniform grain size and crack free microstructure. These results demonstrate that the MSS is a powerful synthesis method to fabricate LLNO at a relatively low temperature while still achieving a high quality material.

Na-ion batteries have attracted recent interest and start now to be counted as viable alternatives vs. Li ion technologies for specific applications. Indeed, recent works on phosphate-based Na-containing positive electrodes such as Na3V2(PO4)3 [1] and Na3V2(PO4)2F3 [2] have demonstrated excellent performances and can be considered as a new step on the way of sodium-ion technology development. However, like for the Li-ion technology, safety issues related to the use of flammable liquid electrolytes remain, especially due to the high reactivity of sodium with moisture and oxygen. All-solid state batteries, which use non-flammable solid electrolytes instead of organic liquid ones, have been proposed as strong candidates for alternative energy storage devices [3-5].
Following a recent successful approach developed for Li-ion all-solid state batteries [6, 7], we were able to assemble a monolithic all-solid state Na-ion battery using NASICON-type electrodes and electrolyte in a single step using the spark plasma sintering technique. Na3V2(PO4)3 was used as both positive (V4+/V3+ couple) and negative (V3+/V2+) electrodes while Na3Zr2Si2PO12 was used as the solid electrolyte. Both compositions present order-disorder phase transitions and present decent ionic conductivities of 1.5 x10 3 S cm-1 and 1.9 x10-4 S cm-1 at 200°C for Na3Zr2Si2PO12 and Na3V2(PO4)3, respectively. Thanks to a new experimental set-up, we report for the first time on the electrochemical characteristics of an all solid state Na-ion battery at temperatures as high as 200°C [8]. The battery operates at 1.8 V with 85% of the theoretical capacity attained at C/10 with good capacity retention, for an overall energy density of 1.87 x10-3 W h cm-2 and a capacity of 1.04 mA h cm-2.
[1]K. Saravanan, C.W. Mason, A. Rudola, K.H. Wong, P. Balaya, Advanced Energy Materials, 3 (2013) 444-450.
[2]A. Ponrouch, R. Dedryvere, D. Monti, A.E. Demet, J.-M. Ateba Mba, L. Croguennec, C. Masquelier, P. Johansson, M.R. Palacin, Energy & Environmental Science, 6 (2013) 2361-2369.
[3]T. Ohtomo, A. Hayashi, M. Tatsumisago, Y. Tsuchida, S. Hama, K. Kawamoto, Journal of Power Sources, 233 (2013) 231-235.
[4]M. Nagao, Y. Imade, H. Narisawa, T. Kobayashi, R. Watanabe, T. Yokoi, T. Tatsumi, R. Kanno, Journal of Power Sources, 222 (2013) 237-242.
[5]S. Boulineau, J.-M. Tarascon, J.-B. Leriche, V. Viallet, Solid State Ionics, 242 (2013) 45-48.
[6]A. Aboulaich, R. Bouchet, G. Delaizir, V. Seznec, L. Tortet, M. Morcrette, P. Rozier, J.M. Tarascon, V. Viallet, M. Dollé, Advanced Energy Materials, 1 (2011) 179-183.
[7]G. Delaizir, V. Viallet, A. Aboulaich, R. Bouchet, L. Tortet, V. Seznec, M. Morcrette, J.-M. Tarascon, P. Rozier, M. Dollé, Advanced Functional Materials, 22 (2012) 2140-2147.
[8]F. Lalère, J.B. Leriche, M. Courty, S. Boulineau, V. Viallet, C. Masquelier, V. Seznec, Journal of Power Sources, 247 (2014) 975-980.