Conductors For Use Research Articles

Ion transport and conduction in metal–organic framework glasses

This perspective highlights an emerging class of metal–organic frameworks (MOFs) with glass transition. They offer advantages like isotropic conduction, absence of grain boundaries, and high moldability, making them promising ion conductors for use in electrochemical and energy related systems.

Physically driven enhancement of the stability of Bi2O3-based ionic conductors via grain boundary engineering

Fast oxygen-ion conductors for use as electrolyte materials have been sought for energy conversion and storage. Bi2O3-based ionic conductors that exhibit the highest known oxygen-ion conductivities have received attention for use in next-generation solid electrolytes. However, at intermediate temperatures below ~600 °C, their conductivities degrade rapidly owing to a cubic-to-rhombohedral phase transformation. Here, we demonstrate that physical manipulation of the grain structure can be used to preserve the superior ionic conductivity of Bi2O3. To investigate the effects of microstructural control on stability, epitaxial and nanopolycrystalline model films of Er0.25Bi0.75O1.5 were fabricated by pulsed laser deposition. Interestingly, in situ impedance and ex situ XRD analyses showed that the grain boundary-free epitaxial film significantly improved the stability of the cubic phase, while severe degradation was observed in the conductivity of its polycrystalline counterpart. Consistently, the cation interdiffusion coefficient measured by the Boltzmann–Matano method was much lower for the epitaxial thin film compared to the polycrystalline thin film. Furthermore, first-principles calculations revealed that the presence of grain boundaries triggered the structural resemblance between cubic and rhombohedral phases, as evidenced by radial distribution functions. Additionally, phase transition energetics predicted that the thermodynamic stability of the cubic phase with respect to the rhombohedral counterpart is reduced near grain boundaries. Thus, these findings provide novel insights into the development of highly durable superionic conductors via microstructural engineering.

Enhanced sintering and electrical properties of proton-conducting electrolytes through Cu doping in BaZr0.5Ce0.3Y0.2O3-δ

To obtain BaZrO3-based electrolyte materials with both good sinterability and high proton conductivity, a Cu-doped B-site BaZr0.5Ce0.3Y0.2-xCuxO3-δ (BZCYCux; x = 0, 0.05, 0.1) system is designed and synthesized. The effects of Cu doping on the crystal structure, sintering and electrical properties of BZCYCux are systematically investigated. The BZCYCu0.05 sample demonstrates the highest sintering density and total conductivity among the studied materials. BZCYCu0.05 can be densified at 1250 °C, which is 300 °C lower than that for unmodified BZCY. The calculated results suggest that the increased conductivity in BZCYCu0.05 benefits from a high apparent specific grain-boundary conductivity, which originates from a small space-charge potential and a large clean part of impurities in the electrolyte. A synthetic analysis based on impedance spectroscopy and distribution of relaxation time further confirms that BZCYCu0.05 is more conductive. A single cell built using the BZCYCu0.05 (∼46 μm) electrolyte shows an excellent power density of 258 mW cm−2 at 700 °C. These results indicate that BZCYCu0.05 is a potential proton conductor for use in protonic ceramic fuel cells.

Investigation of Sputter‐Deposited Thin Films of Lithium Phosphorous Sulfuric Oxynitride (LiPSON) as Solid Electrolyte for Electrochromic Devices

Lithium phosphorus sulfuric oxide nitride (LiPSON) prepared by radio frequency sputtering is investigated as a transparent solid lithium‐ion conductor for use in all‐solid‐state electrochromic (EC) devices. The LiPSON layers are characterized by X‐ray photoelectron spectroscopy (XPS) and their electrical characteristics are studied by temperature‐dependent impedance spectroscopy. Half‐cells of LiPSON deposited on tungsten oxide (WOx) in contact with 1 m LiClO4 in propylene carbonate are studied by electrochemical impedance spectroscopy (EIS) and spectroelectrochemical measurements by cyclic voltammetry and chronoamperometry. A significant influence of LiPSON deposition conditions on the EC characteristics of WOx is observed in the achievable transparency change, as well as the color impression in the bleached and colored state. Formation of a solid−electrolyte interface (SEI) is indicated that leads to poor EC performance with long switching times of 20−60 min. Appropriate deposition conditions for LiPSON are established that maintain a good EC activity of WOx. An all‐solid‐state EC device is assembled of WOx/LiPSON with vanadium titanium oxide as counter electrode and aluminum‐doped zinc oxide as back contact. Temperature‐dependent EIS and spectroelectrochemical measurements show that in such an all‐solid‐state stack, the detrimental contact resistance could be avoided and switching times of less than 60 s are achieved.

Superionic Halogen-Rich Li-Argyrodites Using In Situ Nanocrystal Nucleation and Rapid Crystal Growth.

Although several crystalline materials have been developed as Li-ion conductors for use as solid electrolytes in all-solid-state batteries (ASSBs), producing materials with high Li-ion conductivities is time-consuming and cost-intensive. Herein, we introduce a superionic halogen-rich Li-argyrodite (HRLA) and demonstrate its innovative synthesis using ultimate-energy mechanical alloying (UMA) and rapid thermal annealing (RTA). UMA with a 49 G-force milling energy provides a one-pot process that includes mixing, glassification, and crystallization, to produce as-milled HRLA powder that is ∼70% crystallized; subsequent RTA using an infrared lamp increases this crystallinity to ∼82% within 25 min. Surprisingly, this HRLA exhibits the highest Li-ion conductivity among Li-argyrodites (10.2 mS cm-1 at 25 °C, cold-pressed powder compact) reported so far. Furthermore, we confirm that this superionic HRLA works well as a promising solid electrolyte without a decreased intrinsic electrochemical window in various electrode configurations and delivers impressive cell performance (114.2 mAh g-1 at 0.5 C).

Computational Investigation of Halogen-Substituted Na Argyrodites as Solid-State Superionic Conductors

The discovery of promising inorganic superionic conductors for use as solid-state electrolytes can enable the design of safe and high-energy-density solid-state batteries. Li argyrodites with the c...

Effect of transverse compressive monotonic and cyclic loading on the performance of superconducting CORC® cables and wires

Superconducting CORC® cables and wires have become practical conductors for use in high-field magnets for fusion machines and particle accelerators by demonstrating their ability to carry very high currents in background magnetic fields of up to 20 T. The high mechanical stresses that develop on the CORC® conductor during such operation could result in permanent degradation of the conductor critical current. Transverse compressive stress is one of the predominant mechanical stresses when CORC® cables or wires are bundled into CICCs that allow fusion and detector magnets to operate at currents as high as 100 kA. The effect of transverse compressive load on the critical current of CORC® cables and wires has been investigated at 76 K to determine their irreversible load limit under monotonic loading and load cycling up to 100 000 cycles. The results show a clear effect of the CORC® conductor layout with respect to gap spacing between tapes, thickness of the copper plating surrounding the tapes and thickness of the former onto which the tapes are wound. CORC® cables and wires have demonstrated a remarkable resilience to transverse compressive load cycling where their critical current decreased by no more than a few percent after 100 000 load cycles at peak loads that resulted in an initial decrease in critical current of less than 5%. The results indicate that no significant degradation of CORC® cable and wire performance due to transverse compressive load is expected in large magnets after 100 000 load cycles, as long as the peak load on the conductor does not exceed the irreversible load limit defined at 95% retention in critical current. The irreversible load limit of CORC® conductors could be increased further by increasing the size or hardness of the former that makes up the conductor’s core.

Structure Evolution and Reactivity of the Sc(2- x)V xO3+δ (0 ≤ x ≤ 2.0) System.

Solid oxide fuel cells (SOFCs) are solid-state electrochemical devices that directly convert chemical energy of fuels into electricity with high efficiency. Because of their fuel flexibility, low emissions, high conversion efficiency, no moving parts, and quiet operation, they are considered as a promising energy conversion technology for low carbon future needs. Solid-state oxide and proton conducting electrolytes play a crucial role in improving the performance and market acceptability of SOFCs. Defect fluorite phases are some of the most promising fast oxide ion conductors for use as electrolytes in SOFCs. We report the synthesis, structure, phase diagram, and high-temperature reactivity of the Sc(2- x)V xO3+δ (0 ≤ x ≤ 2.00) oxide defect model system. For all Sc(2- x)V xO3.0 phases with x ≤ 1.08 phase-pure bixbyite-type structures are found, whereas for x ≥ 1.68 phase-pure corundum structures are reported, with a miscibility gap found for 1.08 < x < 1.68. Structural details obtained from the simultaneous Rietveld refinements using powder neutron and X-ray diffraction data are reported for the bixbyite phases, demonstrating a slight V3+ preference toward the 8b site. In situ X-ray diffraction experiments were used to explore the oxidation of the Sc(2- x)V xO3.0 phases. In all cases ScVO4 was found as a final product, accompanied by Sc2O3 for x < 1.0 and V2O5 when x > 1.0; however, the oxidative pathway varied greatly throughout the series. Comments are made on different synthesis strategies, including the effect on crystallinity, reaction times, rate-limiting steps, and reaction pathways. This work provides insight into the mechanisms of solid-state reactions and strategic guidelines for targeted materials synthesis.

Fretting Wear Behaviors of Aluminum Cable Steel Reinforced (ACSR) Conductors in High-Voltage Transmission Line

This work reports the fretting wear behavior of aluminum cable steel reinforced (ACSR) conductors for use in high-voltage transmission line. Fretting wear tests of Al wires were conducted on a servo-controlled fatigue testing machine with self-made assistant apparatus, and their fretting process characteristics, friction force, wear damage, and wear surface morphology were detailed analyzed. The results show that the running regime of Al wires changes from a gross slip regime to a mixed regime more quickly as increasing contact load. With increasing amplitudes, gross slip regimes are more dominant under contact loads of lower than 30 N. The maximum friction force is relatively smaller in the NaCl solution than in a dry friction environment. The primary wear mechanisms in dry friction environments are abrasive wear and adhesive wear whereas abrasive wear and fatigue damage are dominant in NaCl solution.

Status of MgB2 wire and cable applications in Europe

Since its discovery in 2001, MgB2 has generated interest for practical applications. Its availability in the form of multifilamentary round wire makes it suitable for production of cables. Together with relatively high critical temperature and potential low-cost, this renders it appealing for use in superconducting devices where its limited in-field performance can be tolerated. The state-of-the-art properties of commercially available wire and the potential of MgB2 conductors for use in superconducting systems are discussed. An overview of high-current electrical transmission projects where MgB2 has been proposed as an alternative to conventional Nb-Ti or High Temperature Superconductors is presented.

Electronic, elastic, lattice dynamic and thermal conductivity properties of Na3OBr via first principles

Na3OBr is expected to be a promising superionic conductor for use as solid state electrolyte in large scale energy storage systems, but its lattice dynamic and thermal conductivity properties have not been well studied till now. In this work, we performed a detailed study on these properties as well as its electronic and elastic properties using first principles method. The results indicate that Na3OBr is a direct band gap crystal. It is mechanically stable but elastically anisotropic. Its phonons at the Brillouin zone center were classified using group theory analysis and its Born effective charges, LO–TO splitting, and dielectric constants were calculated and discussed. Its phonon dispersion curves were obtained and their origins were revealed. Based on the phonon dispersion curves, its thermal conductivity as a function of temperature was predicted, which give a value of 7.30 Wm−1 K−1 at 300 K. Further study reveals that, for Na3OBr, the simple Slack's model can give almost the same thermal conductivity curve as that obtained from the phonon dispersion curves.

Conductivity and Degradation in Garnet Electrolytes

Lithium-stuffed garnets such as Li7La3Zr2O12 (LLZO) show promise as solid state lithium ion conductors for use in high energy density storage applications due to their chemical and thermal stability and electrochemical performance versus competing electrolytes. Much work has focused on improving the conductivity of these systems by optimising the lithium content through the introduction of lattice vacancies created by the addition of cation dopants (such as Al3+ and Ga3+)1 in the Li sites. The effect of adding cations on the observed Li conductivity depends strongly on the identity and concentration of cations; this process must be tuned such that an optimum number of Li ions and vacancies are present and can readily form an interconnected network of tetrahedral and distorted octahedral sites in the lattice, allowing long-range diffusion. The importance of obtaining the cubic garnet phase which is known to exhibit higher conductivities as a result of increased lithium disorder versus the tetragonal polymorph has been acknowledged and pursued by many.2 In addition, recent observations on the reactivity of the garnets with water have shown that lithium undergoes ion exchange with H+, resulting in a change in conductivity and degradation of the material, accompanied by the formation of passivating Li hydroxide and carbonates at the surface3–5. These phenomena occur even upon ambient air exposure of the garnet samples. Despite this knowledge, little is known about the pathway for lithium and proton diffusion during exchange, and many studies on LLZO garnet materials do not account for the role of this mechanism on the properties reported, with samples freely exposed to an air environment during synthesis and measurement. In this work, we use a Ge(IV) cation substituted at the lithium position to follow the role of aliovalent dopants on the lithium diffusion behaviour, building on previous work using Zn2+ and Ga3+. The high charge Ge4+ ion is chosen to achieve a greater theoretical Li vacancy concentration for the lowest amount of added dopant as a result of charge compensation effects. We have found the critical Li ion to vacancy ratio for optimum ionic conduction in the Ge-doped garnet, using ICP-OES to verify the composition and have measured ionic conductivities of 6-8 x10-4 S cm-1 using AC impedance for the material of nominal composition Li6.6La3Ge0.1Zr2O12. XRD confirms that the cubic garnet structure is stabilised by the addition of Ge. Moreover, the role of moisture in the degradation of LLZO is systematically investigated, through the use of controlled-atmosphere processing (glove box coupled to a high temperature furnace) and deliberate forcing of D/Li exchange in the lattice by exposing the otherwise ‘dry’ samples (synthesised and stored in a protective argon atmosphere) to deuterated water. We use secondary ion mass spectrometry (SIMS) to follow the depth profiles of ion species, specifically Li+, D+ and H+in the undoped and Ge-doped LLZO and have observed diffusion profiles indicative of the exchange process (Figure 1). Preliminary novel work on isotopic Li exchange is underway, following a similar protocol, to calculate the diffusivity in our samples, and the corresponding effect of dopants, stoichiometry and degradation on the observed diffusion profile. Altogether, this work is enabling the fundamental properties of this solid state garnet electrolyte to be better understood, identifying and optimising the factors governing conduction, with a view to its use in high energy density Li-metal batteries. A knowledge of the degradation processes occurring on Li exchange with protons could reveal important conductivity information about these two charge carriers, enabling us to harness this seemingly detrimental behaviour to our advantage.

Spark Plasma Sintering Study on the Super Ionic Glass Ceramic Conductor: Li7P3S11

Solid-state electrolytes that can perform on par with conventional liquid electrolytes are highly sought after for use in all solid-state batteries. An all solid-state battery promises to operate without the possibility of catastrophic failure and have substantially longer self-life than conventional batteries. The Li7P3S11 glass-ceramic is one class of solid electrolytes that could meet the sought after power and reliable performances. We demonstrate a rapid synthesis and densification of the supersonic conductor electrolyte Li7P3S11via spark plasma sintering (SPS) technique. Dense solid-state electrolytes have been formed with a room temperature ionic conductivity is comparable to conventional liquid electrolyte. Hayashi, A., Ishikawa, Y., Hama, S., Minami, T. & Tatsumisago, M. Fast Lithium-Ion Conducting Glass-Ceramics in the System Li[sub 2]S-SiS[sub 2]-P[sub 2]S[sub 5]. Electrochem. Solid-State Lett. 6, A47 (2003).Seino, Y., Ota, T. & Takada, K. A sulphide lithium super ion conductor is superior to liquid ion conductors for use in rechargeable batteries. Energy … 7, 627 (2014).Hayashi, A., Minami, K., Mizuno, F. & Tatsumisago, M. Formation of Li+ superionic crystals from the Li 2S-P2S5 melt-quenched glasses. J. Mater. Sci. 43, 1885–1889 (2008).Minami, K., Hayashi, A. & Tatsumisago, M. Crystallization Process for Superionic Li7P3S11 Glass-Ceramic Electrolytes. J. Am. Ceram. Soc. 94, 1779–1783 (2011).Minami, K., Hayashi, A. & Tatsumisago, M. Crystallization Process for Superionic Li7P3S11 Glass-Ceramic Electrolytes. J. Am. Ceram. Soc. 94, 1779–1783 (2011).Eom, M., Kim, J., Noh, S. & Shin, D. Crystallization kinetics of Li2S–P2S5 solid electrolyte and its effect on electrochemical performance. J. Power Sources 284, 44–48 (2015). Acknowledgments This work was supported by the National Science Foundation under grant number ACI-1053575.

(Invited) Mechanical and Electrochemical Response of All-Solid-State Lithium-Ion Batteries

A suitable theory is required to identify the electro-chemo-mechanical limits of Li-ion batteries performance in realistic electrode-electrolyte configurations. In all-solid cells, the battery life depends in larger measure on the mechanical integrity of the composite system[1]. The proposed fully coupled electro-chemo-mechanical model can contribute to the mesoscale optimization of such composite microstructures [2]. All-solid-state rechargeable lithium-ion batteries have attracted much interest because they have features partic- ularly favorable for large-scale application. The replacement of an organic liquid electrolyte with a non-flammable and more reliable inorganic solid electrolyte (SE) simplifies the battery design and improves safety and durability of the system[3]. However, the mechanical behavior of such electrodes will be considerably different than their liquid electrolyte counterparts. Direct stacking of solid-state cells enables the achievement of high operating voltages in a reduced volume. Furthermore, all-solid-state batteries allow the use of large-capacity electrode materials, for instance sulfur positive electrode paired with a lithium metal negative electrode, which are difficult to employ in conventional liquid electrolyte batteries. A key development to the success of all-solid-state batteries is a SE with high Li+ ion conductivity at room temperature[4, 5, 6]. In recent years, several solid electrolytes having level of conductivity comparable to organic liquid electrolytes have been discovered and tested with many active materials. The durability of a cohering solid- solid interface between electrode and electrolyte is likely to be important practical consideration. Notwithstanding the several techniques investigated to increase the contact area at the interface[7], interface cohesion and its effects on the rate capability and the overall performance throughout the expected life cycles needs to be maintained. The present research focuses on the development of a nonlinear continuum model able to account for the com- bined effects of Li diffusion and for the consequent volumetric expansion of the hosting material. The electrode and electrolyte are modeled as idealized as elastic materials, with elastic properties varying with lithium concentration. The complexity and the multi-physical nature of the problem requires numerical modeling strategies and poses several challenges. To address this, we have established a computational framework based on large deformation theory and in a thermodynamically consistent fashion. This is implemented in an in-house, object oriented C++ numerical code that incorporates three-dimensional finite element calculations. The numerical analysis allows for delamination at the interface between electrode particles and solid electrolyte. Crack formation and propagation is predicted by means of a cohesive zone model extended to include decreased Li flux across interfaces due to their loss of mechanical integrity. Our simulations indicate trends of mechanical reliability of all-solid state batteries realized with some of the most promising solid electrolyte materials (e.g. Li2S-P2S5 [1], LIPON [4], garnet SE [8]); our calculations are based on the mechanical properties available in literature. When physical values for the solid electrolyte’s mechanical behavior are not available, our calculations indicate trends of how mechanical reliability correlates with the battery design and operating conditions (i.e., charging rate). [1] Akitoshi Hayashi, Kousuke Noi, Atsushi Sakuda, and Masahiro Tatsumisago. Superionic glass-ceramic electrolytes for room-temperature rechargeable sodium batteries. Nature Communications, 3, 2012.[2] Giovanna Bucci, Yet-Ming Chaing, and W. Craig Carter. Formulation of the coupled electrochemical-mechanical boundary-value problem, with applications to transport of multiple charged species. Acta Materialia, 2015. (accepted). [3] KazunoriTakada.Progressandprospectiveofsolid-statelithiumbatteries.ActaMaterialia,61(3):759–770,2013. [4] J.B Bates, N.J Dudney, B Neudecker, A Ueda, and C.D Evans. Thin-film lithium and lithium-ion batteries. Solid State Ionics, 135(1 - 4):33 – 45, 2000.[5] Yoshikatsu Seino, Tsuyoshi Ota, Kazunori Takada, Akitoshi Hayashi, and Masahiro Tatsumisago. A sulphide lithium super ion conductor is superior to liquid ion conductors for use in rechargeable batteries. Energy Environ. Sci., 7:627–631, 2014. [6] Noriaki Kamaya, Kenji Homma, Yuichiro Yamakawa, Masaaki Hirayama, Ryoji Kanno, Masao Yonemura, Takashi Kamiyama, Yuki Kato, Shigenori Hama, Koji Kawamoto, and Akio Mitsui. A lithium superionic conductor. Nature materials, 10(9):682–6, September 2011.[7] Masahiro Tatsumisago, Motohiro Nagao, and Akitoshi Hayashi. Recent development of sulfide solid electrolytes and interfacial modification for all-solid-state rechargeable lithium batteries. Journal of Asian Ceramic Societies, 1(1):17 – 25, 2013.[8] Ezhiyl Rangasamy, Jeff Wolfenstine, and Jeffrey Sakamoto. The role of Al and Li concentration on the formation of cubic garnet solid electrolyte of nominal composition Li7La3Zr2O12. Solid State Ionics, 206(0):28 – 32, 2012.

Silver nanowire purification and separation by size and shape using multi-pass filtration

Silver nanowire (AgNW) meshes produced by soft solution polyol synthesis offer a low-cost low-temperature solution deposited alternative to indium tin oxide (ITO) transparent conductors for use in solar cells. However, polyol synthesis typically produces both nanoparticles and nanowires during synthesis. Nanoparticles reduce optical transmission of nanowire meshes without any beneficial reduction to sheet resistance. This work describes a combined purification and separation multi-pass filtration process to efficiently remove nanoparticles from nanowire solutions before deposition. The filtered samples typically contains 86% nanowires (14% nanoparticles) compared to 67% nanowires in the standard centrifuge process and 55% nanowires in the original sample. The filtration method offers further benefits of reduced nanowire breakage and a generally lower sheet resistance after nanowire deposition.

Revealing Conduction Mechanisms in Lithium-Rich Garnets Using Aliovalent Dopants

Lithium stuffed garnets such as Li7La3Zr2O12 (LLZO) show promise as solid state lithium ion conductors for use in high energy density storage applications due to their chemical and thermal stability and electrochemical performance versus current technology electrolytes. Much work has focused on improving the conductivity of these systems by optimizing the lithium content in the cubic garnet phase rather than the less conducting tetragonal polymorph1. Despite extensive studies on these materials, there is uncertainty as to the preferred migration of Li; whether the ions move from one octahedral (Oh) site to another via a neighbouring tetrahedron (Oh-Td-Oh path), or hop directly across Oh sites, bypassing the Td site (Oh-Oh path), is still up for debate2,3. We seek to confirm the lattice site occupancy of the mobile lithium ions and their associated conduction pathways by varying the lithium-substituted dopant species (Ga, Zn, Ge), thereby blocking Li movement through one of the two paths. The effect of dopant charge and ionic radius on cubic phase stabilization (as a result of Li concentration) and lattice strain is studied. Moreover, the moisture sensitivity of Li-conductor ceramics has been recently associated with a deterioration of Li transport4 and density of the material, of great importance in battery applications5. In this study, we use an argon-supplied glove box coupled to a furnace for processing and synthesis, preventing proton exchange with Li, thus avoiding the creation of proton charge carriers and improving the densification to above 90% relative density. This is fundamental to analyze the real Li-conduction mechanism and optimize the Li conductivity in garnets. To study the degradation process of lithium displacement by protons in moisture, and the effect of the protons on the ionic conductivity, we conduct isotopic exchange experiments on the samples using H2O and D2O followed by secondary ion mass spectroscopy. The total conductivity of the samples is found by AC impedance in a range of humidities and temperatures. X-ray diffraction and neutron diffraction are employed to determine the structural features, specifically to localize the dopants, Li and protons and to analyse the conduction pathways as a function of the dopant. References 1J. Awaka et al.(2009) J. Solid State Chem. 182, 2046-2052 2 Han, J. et al. (2012) Chem. Commun., 48 (79), 9840–9842 3 Xu, M. et al. (2012) Phys .Rev. B, 85, 052301 4Aguesse, F. et al. (2014) Adv. Mater. Interfaces, 1 (7), 1300143 5 Bernuy-Lopez, C. et al. (2014) Chem. Mater., 26 (12), 3610-3617 Figure 1

Modeling the Mechanical and Electrochemical Response of All-Solid-State Lithium-Ion Batteries

All-solid-state rechargeable lithium-ion batteries have attracted much interest recently for applications of much larger scale than previous thin-film batteries. The replacement of an organic liquid electrolyte with a non-flammable inorganic solid electrolyte (SE) may simplify battery design and improve safety and durability [2]. However, in all-solid cells, the battery life depends in large measure on the mechanical integrity of the composite system [1]. A suitable theory to identify the electro-chemo-mechanical limits of Li-ion batteries performance in realistic electrode-electrolyte configurations is therefore required. In this work, a fully coupled electro-chemo-mechanical model is developed to facilitate the mesoscale optimization of such composite microstructures. A key development in all-solid-state batteries has been the discovery of solid electrolytes with high Li+ ion conductivity at room temperature comparable to that of organic liquid electrolytes [3, 4, 5]. These have been tested with numerous electrode active materials.The durability of a coherent solid-solid interface between electrode and electrolyte is likely to be an important consideration. Notwithstanding the several techniques investigated to increase the contact area at the interface [6], interface cohesion and its effects on the rate capability and the overall performance throughout the expected life cycles needs to be maintained. In the present research, we develop a nonlinear continuum model able to account for the combined effects of Li diffusion and for the consequent volumetric expansion of the hosting material. The electrode and electrolyte are idealized as elastic materials with elastic properties varying with lithium concentration. The complexity and the multi-physical nature of the problem require numerical modeling strategies and pose several challenges. To address this, we have established a computational framework based on large deformation kinematics and posed in a thermodynamically consistent fashion. The model is implemented in an in-house, object oriented C++ numerical code that incorporates three-dimensional finite element calculations. The numerical analysis allows for delamination at the interface between electrode particles and solid electrolyte. Crack formation and propagation is predicted by means of a cohesive zone model extended to include decreased Li flux across interfaces due to their loss of mechanical integrity. Our simulations indicate trends of mechanical reliability of all-solid state batteries realized with some of the most promising solid electrolyte materials (e.g. Li2S-P2S5 [1], LIPON [3], garnet SE [7]), using mechanical properties available in literature. When physical values for the solid electrolyte’s mechanical behavior are not available, the simulations indicate trends of how mechanical reliability correlates with the battery design and operating conditions (i.e., charging rate). Acknowledgments The work was supported by the grant DE-SC0002633 funded by the U.S. Department of Energy, Office of Science. Keywords Lithium ion batteries, All-solid-state batteries, Nonlinear continuum mechanics; Diffusion; Thermodynamics References [1] A. Hayashi, K. Noi, A. Sakuda, and M. Tatsumisago. Superionic glass-ceramic electrolytes for room-temperature rechargeable sodium batteries. Nature Communications, 3, 2012. [2] K. Takada. Progress and prospective of solid-state lithium batteries. Acta Materialia, 61(3):759 – 770, 2013. [3] J.B Bates, N.J. Dudney, B. Neudecker, A. Ueda, and C.D. Evans. Thin-film lithium and lithium-ion batteries. Solid State Ionics, 135(1 - 4):33 – 45, 2000. [4] Y. Seino, T. Ota, K. Takada, A. Hayashi, and M. Tatsumisago. A sulphide lithium super ion conductor is superior to liquid ion conductors for use in rechargeable batteries. Energy Environ. Sci., 7:627–631, 2014. [5] N. Kamaya, K. Homma, Y. Yamakawa, M. Hirayama, R. Kanno, M. Yonemura, T. Kamiyama, Y. Kato, S. Hama, K. Kawamoto, and A. Mitsui. A lithium superionic conductor. Nature materials, 10(9):682–6, September 2011. [6] M. Tatsumisago, M. Nagao, and A. Hayashi. Recent development of sulfide solid electrolytes and interfacial modification for all-solid-state rechargeable lithium batteries. Journal of Asian Ceramic Societies, 1(1):17 – 25, 2013. [7] E. Rangasamy, J. Wolfenstine, and J. Sakamoto. The role of Al and Li concentration on the formation of cubic garnet solid electrolyte of nominal composition Li7La3Zr2O12. Solid State Ionics, 206(0):28 – 32, 2012. Figure 1: Simulation of a composite all-solid Li-ion battery microstructure upon lithiation. The diffusion fronts (white lines) appear perturbed due to partial delamination of the interface between electrode particles and solid electrolyte. Figure 1

Revealing the Li Conduction Pathway Using Dopants at the Li Sites in Stuffed Garnets

Lithium-rich garnets such as Li7La3Zr2O12 (LLZO) show promise as solid state lithium ion conductors for use in high energy density storage applications due to their chemical and thermal stability and electrochemical performance versus current technology electrolytes. Much work has focused on improving the conductivity of these systems by maximizing the lithium content but also through the introduction of lattice vacancies created by the addition of cation dopants (such as Ga1) in the Li sites. Additionally, the importance of stabilizing the cubic garnet phase as opposed to the less conducting tetragonal polymorph has been acknowledged and pursued in the search for high conductivities2. There is uncertainty with regard to the specific Li ion conduction mechanism in these systems however it is widely agreed that the Li ions in LLZO adopt tetrahedral (Td) and octahedral (Oh) positions in the lattice and that the conduction pathway is by a face-sharing network of these sites3, 4. It is yet unclear if the Li ions move from one Oh site to another via a neighbouring Td site (Oh-Td-Oh path), or whether they hop directly across Oh sites, bypassing the Td site (Oh-Oh path), and how this pathway is influenced by the lattice site occupancy of Li and dopants. The sensitivity to air and moisture during synthesis5as well as phase transformations of the garnet structure further complicate the picture. In this study, we determine the exact nature of the effect of dopants on the conductivity by investigating the dopant species Zn(II), Ga(III) and Ge(IV). An understanding of the lattice position adopted by these cations as determined by their size and/or charge will be achieved through analysis of the synthesized samples by neutron diffraction and solid state NMR. By tracking the dopant ion position, the corresponding Li conduction pathway can be found and related to that required for optimum conductivity. We also find the critical Li ion to vacancy ratio for optimum ionic conduction, by varying the stoichiometry of each dopant of a particular oxidation number and measuring the resultant electrolyte ionic conductivity using an AC impedance technique. Lattice strain effects will be a final consideration- how does the size of the dopant ion restrict or enhance the diffusion pathway of the Li ions, and is there a blocking effect seen above certain dopant concentrations? Control of the atmospheric conditions is achieved throughout by the use of an Argon-supplied glovebox coupled with a furnace (1600°C), preventing exchange of Li with H+during synthesis and processing. This has proven to improve the densification of the electrolyte and increase the Li-conductivity by between 1 and 3 orders of magnitude. Figure 1. a) Arrangement of polyhedra in the garnet Ga-doped LLZO cubic structure and b) Possible Li-pathways in the Td-Oh network.1 References [1] Bernuy-Lopez, C. et al. (2014) Chem. Mater., 26 (12), 3610-3617 2 J. Awaka et al.(2009) J. Solid State Chem.182, 2046–2052 3 Han, J. et al. (2012) Chem. Commun., 48 (79), 9840–9842 4 Xu, M., et al. (2012) Phys .Rev. B, 85, 052301 5 Aguesse, F. et al. (2014) Adv. Mater. Interfaces, 1 (7), 1300143 Figure 1

A sulphide lithium super ion conductor is superior to liquid ion conductors for use in rechargeable batteries

We report that a heat-treated Li2S–P2S5 glass-ceramic conductor has an extremely high ionic conductivity of 1.7 × 10−2 S cm−1 and the lowest conduction activation energy of 17 kJ mol−1 at room temperature among lithium-ion conductors reported to date. The optimum conditions of the heat treatment reduce the grain boundary resistance, and the influence of voids, to increase the Li+ ionic conductivity of the solid electrolyte so that it is greater than the conductivities of liquid electrolytes, when the transport number of lithium ions in the inorganic electrolyte is unity.

Characterization of Mechanical Properties of MgB2 conductor for Superconducting Link Project at CERN

In the framework of high luminosity upgrade of Large Hadron Collider at CERN, superconducting links are being developed. MgB2 wire is a candidate conductor for use in high- current cables. Mechanical properties of this material are of key importance for the definition of the cable design and operating conditions. In this study, we evaluated the Young’s modulus of MgB2 filaments extracted from ex situ processed composite wires. The wires were produced in unit lengths of about 1 km and used in high-current cables. Single fiber tensile test was carried out on fil- aments composed of MgB2, Nb barrier, and Nb–Ni reaction layer. From the unloading modulus of filament specimens measured with different gauge lengths, the Young’s modulus of composite filaments extracted from two different strands was determined to be 114 and 122 GPa at room temperature, respectively. By using the rule-of-mixture, the Young’s modulus of MgB2 was estimated to be lower than that reported for highly dense MgB2 bulks. The reason for such difference is discussed from the viewpoint of void fraction.