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Instability of nickel-rich layered oxides at high voltages is an impediment to their wider use in Li-ion batteries. HF generated via LiPF6 hydrolysis accelerates corrosion, further destabilizing th...

Safe, fast, and energy efficient cycling of lithium ion batteries is desired in many practical applications. However, modeling studies predict steep Li+ ion gradients in the electrodes during cycling at the higher currents. Such gradients introduce heterogeneities in the electrodes, which make it difficult to predict cell lifetimes as different portions of the cell age at different rates. There is a dearth of experimental methods to probe these concentration gradients across the depth of the electrode. Here we use spatially resolved energy dispersive X-ray diffraction to obtain a “movie” of lithiation and delithiation in different sections of the cell and quantify lithium gradients that develop in a porous graphite electrode during cycling at a 1C rate. Inhomogeneity in the total Li content, and in the individual ordered LixC6 phases formed during lithium insertion into (and extraction from) the graphite, has been observed in an operando fashion. The complex dynamics of lithium-staging in graphite with the distinct front propagation of phase changes have been characterized and new features of these dynamics are highlighted here. As large Li+ ion gradients contribute to cell polarization, our results suggest that Li plating conditions can be met near the graphite electrode surface, even when the cell is charged at a moderate (1C) rate.

Rapid charging of lithium-ion batteries being developed for electric vehicles is a formidable challenge. Electrochemical polarization of cells during fast charging favors deposition of metallic Li onto the surface of the graphite electrode, and this Li plating compromises safety and accelerates performance degradation. Observing the onset of Li nucleation is essential for elucidation of mechanisms and defining conditions favoring this Li plating, but presently available methods are not sufficiently sensitive and selective while also allowing satisfactory spatial resolution. Here we demonstrate the use of Raman spectroscopy as a sensitive means to identify Li nucleation and map Li deposition. Metallic Li is detected indirectly by probing the vibrations in an acetylide species (represented as Li—C≡C—X) that is formed on the exposed surface of Li nuclei in contact with the solid electrolyte interphase on graphite. Surface-enhanced Raman scattering (SERS) involving this species on Li nuclei appears to dramati...

Temperature imposes a diversified set of problems to the successful operation of Li-ion batteries. Graphite anodes, in particular, are especially fragile at elevated temperatures, as continuous electro-reduction processes cause detrimental transformations in the solid electrolyte interphase (SEI). In the present work, we investigate the factors that contribute to the performance decay of graphite in cells containing a pyrrolidinium-based ionic liquid, exploring the effect of different lithium salts, electrode formulations and test conditions on the thermal resilience of the system. We show that the contribution of FSI anions to the SEI provides remarkable protection to graphite particles, preventing the electronic isolation of electrode domains. We further propose that the positive activity exhibited by these species is associated with their specific decomposition pathway. A coulombic efficiency of 99.4% could be achieved in Li/graphite half-cells at 90 °C, demonstrating that compositional control of the solid electrolyte interphase is essential to extend the environmental range of Li-ion batteries.

Structural and stoichiometric alterations in cathode materials with high intercalation voltages have been a bottleneck for next generation lithium ion batteries. Moreover, structure damage with the slightest of temperature elevation is predominant in known cathode systems. Monoclinic Li3V2(PO4)3 (LVP) with high intercalation voltage (>4.0 V) is a potential high-power cathode for lithium ion batteries owing to extraordinary stability of the phosphate anion framework. However, severe vanadium dissolution and lattice re-arrangement remains the biggest nuisance. Modification of electron conduction pathways by doping LVP lattice with Cr3+ is studied here and the efficacy of Cr3+ to stabilize the structure is understood. Vacant d-orbital sites in Cr3+ promote de-localization of electrons suppressing disproportionation and hence vanadium dissolution resulting in improved electrochemical performance for robust cycling conditions. Significant enhancement in specific capacity retention (from 26% to 84%) and improved cycle life of 400 high power cycles was observed on doping suggesting excellent performance of the cathode at high temperature (60 °C) environments.

In the evaluation of compatibility of different components of cell for high-energy and extreme-conditions applications, the highly focused are positive and negative electrodes and their interaction with electrolyte. However, for high-temperature application, the other components are also of significant influence and contribute toward the total health of battery. In present study, we have investigated the behavior of aluminum, the most common current collector for positive electrode materials for its electrochemical and temperature stability. For electrochemical stability, different electrolytes, organic and room temperature ionic liquids with varying Li salts (LiTFSI, LiFSI), are investigated. The combination of electrochemical and spectroscopic investigations reflects the varying mechanism of passivation at room and high temperature, as different compositions of decomposed complexes are found at the surface of metals.

Both flexible energy harvesting and storage devices have been widely reported separately to satisfy part of the needs in the emerging areas, including wearable electronics, and low-density applications such as rooftop solar collectors. However, a flexible energy system with mechanical robustness and light-weight is the integrated device that will serve the real demand. Herein, a flexible printable dye-sensitized solar cell/supercapacitor integrated energy device has been designed, fabricated and characterized. This new device has several advantages: flexible, portable, high voltage capacity (up to 1.8 V), lightweight, environmental friendly and expanded indoor-use capabilities. The device demonstrated very stable performances under various extreme mechanical loading conditions in outdoor testing. This work paves way for future development of highly flexible integrated energy system for many potential applications.

In this study, Auger electron spectroscopy (AES) combined with ion sputtering depth profiling, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) have been used in a complementary fashion to examine chemical and microstructural changes in graphite (Gr) and silicon/graphite (Si/Gr) blends contained in the negative electrodes of lithium-ion cells. We demonstrate how AES depth profiling can be used to characterize morphology of the solid electrolyte interphase (SEI) deposits in such heterogeneous media, complementing well-established methods, such as XPS and SEM. In this way we demonstrate that the SEI does not consist of uniformly thick layers on the graphite and silicon; the thickness of the SEI layers in cycle life aged electrodes follows an exponential distribution with a mean of ca. 13 nm for the graphite and ca. 20–25 nm for the silicon nanoparticles (with a crystalline core of 50–70 nm in diameter). A “sticky-sphere” model, in which Si nanoparticles are covered with a layer...

Recent interest in developing cathode materials for an elevated temperature operation of Li-ion batteries has motivated researchers to explore the possibility of using layered V2O5 as a potential candidate because of its high capacity and cyclic stability. Despite a wide lithiation voltage window of V2O5 (between 1.0 V and 4.0 V), compositional fluctuations, metal dissolution, and so on contribute to capacity loss at high temperatures. A first discharge of V2O5 to voltages below 2.0 V has been observed to be associated with a series of phase transformations at both room temperature and high temperature and has been characterized here. From structural characterization of harvested electrodes post–first discharge, a new Li-rich phase was observed to be formed at 120°C and the composition was estimated.

Three-dimensionally structured architectures are known to improve the performance of electrodes used in Li ion battery systems. In addition, integration of select 2D materials into 3D structures, for enhancing both electrical conductivity and electrochemical activity, will prove advantageous. Here a scalable one-step chemical vapor deposition technique is demonstrated for the controlled etching and simultaneous graphene growth on stainless steel substrates resulting in a 3D micro-mesh architecture that is ideal for high rate/high capacity electrodes; the graphene coated 3D stainless steel current collector is used with an MoS2 electrode material for demonstrating high stability and rate capacity in Li-ion batteries.

Extending operating voltage of Li-ion batteries results in higher energy output from these devices. High voltages, however, may trigger or accelerate multiple processes responsible for long-term performance decay. Given the complexity of physical processes occurring inside the cell, it is often challenging to achieve a full understanding of the root causes of this performance degradation. This difficulty arises in part from the fact that any electrochemical measurement of a battery will return the combined contributions of all components in the cell. Incorporation of a reference electrode can solve part of the problem, as it allows the electrochemical reactions of the cathode and the anode to be individually probed. A variation in the voltage range experienced by the cathode, for example, can indicate alterations in the pool of cyclable lithium ions in the full-cell. The structural evolution of the many interphases existing in the battery can also be monitored, by measuring the contributions of each electrode to the overall cell impedance. Such wealth of information amplifies the reach of diagnostic analysis in Li-ion batteries and provides valuable input to the optimization of individual cell components. In this work, we introduce the design of a test cell able to accommodate multiple reference electrodes, and present reference electrodes that are appropriate for each specific type of measurement, detailing the assembly process in order to maximize the accuracy of the experimental results.

Rechargeable batteries capable of operating at high temperatures have significant use in various targeted applications. Expanding the thermal stability of current lithium ion batteries requires replacing the electrolyte and separators with stable alternatives. Since solid-state electrolytes do not have a good electrode interface, we report here the development of a new class of quasi-solid-state electrolytes, which have the structural stability of a solid and the wettability of a liquid. Microflakes of clay particles drenched in a solution of lithiated room temperature ionic liquid forming a quasi-solid system has been demonstrated to have structural stability until 355 °C. With an ionic conductivity of ∼3.35 mS cm(-1), the composite electrolyte has been shown to deliver stable electrochemical performance at 120 °C, and a rechargeable lithium battery with Li4Ti5O12 electrode has been tested to deliver reliable capacity for over several cycles of charge-discharge.

A self-assembled MoSe2 nanolayers/reduced graphene oxide (MoSe2/rGO) foam was prepared using a hydrothermal method. The samples were systematically investigated by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and high-resolution transmission electron microscopy. Electrochemical performances were evaluated in two-electrode cells versus metallic lithium. It is demonstrated that the obtained MoSe2/rGO nanocomposites show three-dimensional architecture and excellent electrochemical performance as anode materials for Li-ion batteries. The specific capacity of MoSe2/rGO anode can reach up to 650 mAh g−1 at a current rate of 0.1C in the voltage range 0.01–3.0 V (vs. Li/Li+), which is higher than the theoretical capacity of MoSe2 (422 mAh g−1). Additionally, the fabricated half cells have shown good rate capability and long cycling stability with 10.9% capacity loss after 600 cycles under a current density of 0.5C. The excellent performance of the synthesized MoSe2/rGO is attributed to its unique nanostructure, including nanolayered MoSe2, highly conductive rGO networks and mechanically stable 3D architecture.

Nanosized silicon materials are being developed for use in the anodes of high-energy lithium-ion batteries. However, the high surface areas of these materials increase the rate of parasitic reactions in the electrode, which consume cyclable Li+ and degrade battery performance. Prelithiation offers a realistic strategy to compensate for this reactivity, by injecting additional charge into the cell to counterbalance the Li+ loss. Interestingly, the benefits offered by prelithiation extend beyond its more obvious purpose. Here, by using a reference electrode in NMC532//Si–Gr cells, we show how prelithiation alters the cycling potentials experienced by the Si-containing anode and how that translates into gains in cycle life. The rate of consumption of the prelithiated charge is lower than that expected from the behavior of non-prelithiated cells. Curiously, the Si particles become partially unresponsive during the C/3 cycling apparently because of kinetic constraints. Electrochemical studies on harvested electrodes in half-cells show that capacities are intact after the long-term cycling and that most of the lithium reservoir is still present in the anode. We conclude that the high capacity retention displayed by the prelithiated cells mainly results from a higher participation of graphite particles during the extended electrochemical cycling.

Symmetric cells provide complementary means to probe electrochemical processes in lithium-ion batteries. Here, positive and negative electrodes harvested from conventional oxide/graphite cells are cross-paired, and the assembled reference-electrode-bearing symmetric cells are cycled/aged. For graphite symmetric cells, the electrode potentials and impedances remain nearly constant during calendar aging and the parasitic currents are typically small. However, at higher cell voltages when the “positive” graphite potential exceeds 1.0 V vs. Li/Li+, the capacity loss is higher, indicating that even a mild (but prolonged) overdischarge can damage the SEI. For the layered-oxide symmetric cells there are strong parasitic currents and a persistent slide of the electrode potential over time during calendar aging. Significant cell impedance rise, especially at higher hold voltages, is also observed. Curiously, the impedance rise in the “negative” oxide electrode, which experiences potentials below 4.0 V vs. Li/Li+, is greater than in the “positive” oxide electrode that experiences much higher potentials. We postulate that electrolyte oxidation is responsible for the behavior of these oxide symmetric cells, as it supplies electrons (that bind more Li+ into the cathode, causing the potential slide) and protons (that contribute to impedance rise). These insights can guide the development of future lithium-ion cell chemistries.

Safe and energy efficient fast charging of lithium ion batteries is desired in many practical applications such as portable electronics and electrified transportation. However, diffusive transport modeling predicts steep intercalant gradients in the electrodes during high-current cycling. The heterogeneities in the electrodes created by these gradients negatively impacts battery lifetimes as mechano-chemical stresses develop in the structure of the cell’s electrodes. Direct experimental measurement of these gradients is lacking to steer pragmatic optimization of Li-Ion electrodes for gradient-free fast utilization. In this talk, we will discuss the novel use of spatially resolved energy dispersive X-ray diffraction to obtain a direct spatiotemporal "movie" of insertion and de-insertion in different sections of the cell and quantify gradients in lithium distribution that develop in a typical graphite electrode during one-hour full charges and discharges. We discovered, even at this moderate charge/discharge rate, that unexpectedly large spatial inhomogeneities in the ordered LixC6 phases and thereby in Li-content are prevalent causing mechano-chemical stresses in the cell. In the specific case of the typical graphite with reversible potential perilously close to that of metallic lithium, these steep gradients polarize the battery cell on charge and lithium plating conditions can be met near the electrode surface resulting in the potential for dendrite-induced short circuits and compromised fire safety. Figure 1

The demand for high energy densities in Li-ion batteries (LIBs) necessitates exploring bottlenecks of cell performance. Layered oxide positive electrodes, such as LiNixCoyMn1-x-yO2 (NCM), and silicon-graphite composite (Si-Gr) negative electrodes in a LIB undergo a series of complex structural and compositional changes during electrochemical cycling. The induced changes have a direct influence on the energy and power output from a battery and a profound dependence on the cycling or aging conditions. The promise of multifold enhancement in energy densities of LIBs using Si based negative electrodes is accompanied by the limited stability of the electrode-electrolyte interface. In commercial LIBs, the solid electrolyte interphase (SEI) layer on the graphite negative electrode facilitates Li+ ion conduction and minimizes reduction of the electrolyte. In cells with Si- containing negative electrodes, the large volume changes of Si during cycling results in continuous degradation of the SEI layer. The formation of a new SEI on the newly-exposed Si surfaces during subsequent cycling causes further trapping of Li+ ions, contributing to performance loss. In the present study, full cells with NCM 523 cathode, Si-Gr (containing 15 wt% Si) anode, and a baseline electrolyte (1.2 M LiPF6 in Ethylene Carbonate/Ethyl Methyl Carbonate, 3:7 w/w) were tested under calendar life ageing and cycle life ageing protocols between 3 and 4.1 V. The cycle-life cells showed ~92% capacity loss after 100 cycles, while the calendar-life cells showed ~13% capacity loss; the reasons for this difference will be highlighted during the presentation.1 In order to further improve capacity retention we studied the effect of various additives to the baseline electrolyte, and also examined EC-free electrolyte systems. Advanced diagnostic techniques, including X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM) were used to examine the effect of these additives on the SEI layer.2,3 Insights from electrochemical response in conjunction with post-mortem characterization studies have fostered deeper understanding of the charge transfer mechanisms and the properties of the interfacial layers in the blended negative electrodes. Fundamental knowledge of the nature of this dynamic SEI layer is essential to design better surface films and achieve stable electrochemical cycling. Support from David Howell, Brian Cunningham, and Peter Faguy of the U.S. Department of Energy’s Office of Vehicle Technologies is gratefully acknowledged. This work was performed under the auspices of the US Department of Energy, Office of Vehicle Technologies, Hybrid and Electric Systems, under Contract No. DE-AC02-06CH11357 K. Kalaga et al., manuscript in preparation (2017). K. Kalaga, I.A. Shkrob, R.T. Haasch, C. Peebles, J. Bareño, D.P. Abraham, “Auger Electrons as Probes for Composite Micro and Nanostructured Materials: Application to Solid Electrolyte Interphases in Graphite and Silicon-Graphite Electrodes”, J. Phys. Chem. C 2017, 121, 23333−23346. J. Bareño, I.A. Shkrob, J.A. Gilbert, M. Klett, D.P. Abraham, “Capacity Fade and Its Mitigation in Li-ion Cells with Silicon-Graphite Electrodes”, J. Phys. Chem. C 121 (2017), pp 20640-20649.

Electromobility demands higher energies and power densities, greater thermal safety, and lower cost compared to the ubiquitous LiCoO2 batteries. This demand is fueling the development of new intercalation cathode materials for Li-ion batteries. The LixNi(1-y-z)CoyMnzO2 (NCM) series oxides have garnered interest in this regard for the following reasons: (i) their high capacities approaching 200 mAh·g-1 NMC afforded by the double redox center of Ni1, 2 is significantly greater than that of LiCoO2 (LCO) which has stable capacities of ~140 mAh·g-1 LCO;3 (ii) their anticipated cost is lowered by partial substitution of Co with Ni and Mn; (iii) exothermic thermal reactivity is pushed up to ~270 °C compared to ~190 °C for LiCoO2.2, 4 With their advantages clear, the choice of an NCM oxide is a tradeoff between transition metal ratios, relative capacities, relative stability, relative cost, and relative power capability. Fast charging/discharging is becoming more and more central to the practicality of electric vehicles; hence, knowledge of Li+ ion diffusion through the oxide structure is important. We investigated the influence of transition metal ratios on Li+ ion diffusion as a function of state of charge in NCM424, NCM523, NCM622, and NCM811 using the galvanostatic intermittent titration technique. An example for the NCM523 oxide is shown in Figure 1. We utilized synchrotron-based operando energy dispersive X-ray diffraction (EDXRD) to relate the Li+ ion diffusion coefficients to crystallographic evolution during the oxide delithiation-lithation process. We will describe these relationships during our presentation. Additionally, the diffusion coefficient values are related to the fast charging performance of the oxides to elucidate their importance to practical applications. References: 1. Wei, Y., et al., Kinetics Tuning of Li-Ion Diffusion in Layered Li(NixMnyCoz)O2. J. Am. Chem. Soc., 2015. 137(26), 8364. 2. Yabuuchi, N. and T. Ohzuku, Novel lithium insertion material of LiCo1/3Ni1/3Mn1/3O2 for advanced lithium-ion batteries. J. Power Sources, 2003. 119–121, 171. 3. Ozawa, K., Lithium-ion rechargeable batteries with LiCoO2 and carbon electrodes: the LiCoO2/C system. Solid State Ionics, 1994. 69(3), 212. 4. Cho, J. and G. Kim, Enhancement of Thermal Stability of LiCoO2 by LiMn2O4 Coating. Electrochem. Solid-State Lett., 1999. 2(6), 253. Acknowledgement: The electrodes and electrolytes are from Argonne’s Cell Analysis, Modeling and Prototyping (CAMP) Facility, which is supported within the core funding of the Applied Battery Research (ABR) for Transportation Program. We acknowledge the assistance of S. Trask, B. Polzin, A. Jansen, and D. Dees during the course of this work. Support from the U.S. Department of Energy’s Vehicle Technologies Program (DOE-VTP) is gratefully acknowledged. This document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. Figure 1 Caption: Diffusion coefficients in NCM523 oxide as a function of Li content using GITT. In order to account for the effect of duration of the polarization step, diffusion coefficients were estimated as the average of values calculated from the GITT formula using 300, 350, 400, 450, 500, 550, 600 seconds of the polarization step. Each curve contains the average data obtained from three separate cells. Error bars are three standard deviations resulting from the averaging of three cells. Note that the scatter (standard deviation) on averaging three separate cells is generally greater than the scatter from averaging the various time intervals selected. Square symbols indicate charging while circle symbols indicate discharge. Figure 1

Improvements in the energy density of lithium-ion batteries (LIBs), through the adoption of novel high capacity anodes as alternatives to graphite, are being widely pursued. Silicon, with a theoretical capacity of 3579 mAh g-1, lithiation voltage comparable to that of graphite, and high abundance, is considered the most appropriate alternative. The advantages of high energy density are countered by severe capacity fade, limiting the cycle life of Si-containing cells. Fundamental mechanistic understanding of lithiation and de-lithiation processes in Si-electrodes is essential to identify causes of capacity loss. Several in-situ and ex-situ microscopy and spectroscopy techniques have provided information on structural, chemical, and morphological changes of electrodes at specific states of charge and during calendar/cycle life ageing. We adopted Energy Dispersive X-ray diffraction (EDXRD) to track structural changes in all components of pure Graphite (Gr) and Silicon/Graphite (Si/Gr = 15/73 w/w) based lithium-ion cells. Beamline 6 A-B at the Argonne Photon Source (APS), equipped with a fixed 3º angle single element Ge detector and incident white X-ray beam was used to obtain in operando EDXRD spectra from CR2032-type coin cells. The coin cells were assembled with a Li metal counter electrode, and 1.2 M LiPF6 in EC/EMC (3:7 w/w) + 10 wt% FEC as the electrolyte, and underwent electrochemical cycling at a ~C/8 rate. Lattice parameters corresponding to the spectral peaks were derived from the energy of the diffracted X-rays. Variations in the average Gr layer spacing during lithiation of the pure Gr half-cell was used to calibrate an “average layer spacing vs. state of lithiation” in the Gr-component. The lattice parameters of different phases formed upon lithiation and delithiation of Si and graphite were estimated which can, thus, be used to obtain the extent of lithiation in Si and in graphite quantitatively at every state-of-charge. The consequences of this lithiation-delithiation behavior will be highlighted during our presentation. Acknowledgement: The authors acknowledge colleagues at Argonne, especially S. Trask, B. Polzin, A. Jansen, and D. Dees. The electrodes and electrolytes are from Argonne’s Cell Analysis, Modeling and Prototyping (CAMP) Facility, which is supported within the core funding of the Applied Battery Research (ABR) for Transportation Program. Support from the U.S. Department of Energy’s Vehicle Technologies Program (DOE-VTP), specifically from Peter Faguy, is gratefully acknowledged. This document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357.

Lithium-ion cells containing layered-oxide based positive electrodes and graphite-based negative electrodes are being cycled at high voltages (> 4.30 V) to increase energy density. In this presentation we will detail performance changes in these cells during cycling, with a particular focus on the crosstalk between electrodes. We show that the dissolution of transition metal (TM) ions from the positive electrode, and their migration and incorporation into the solid electrolyte interphase (SEI) of the negative electrode, accelerates markedly as the upper cutoff voltage (UCV) exceeds 4.30 V. At voltages ≥ 4.40 V there is enhanced fracture of the oxide during cycling that creates new surfaces and causes increased solvent oxidation and TM dissolution. Despite this deterioration, cell capacity fade still mainly results from lithium loss in the negative electrode SEI. Among TMs, Mn content in the SEI shows a better correlation with cell capacity loss than Co and Ni contents. We estimate that each Mn ion deposited in the SEI causes trapping of ~100 additional Li+ ions thereby hastening the depletion of cyclable lithium ions. During the presentation we will highlight an electrocatalysis mechanism through which the deposited Mn ions accelerate electrolyte reduction and increase Li trapping in the negative electrode SEI. Methods to mitigate this cross-talk, through the use of coatings and additives, will also be discussed.

With its exceptional theoretical charge capacity, silicon holds great promise as an anode material for realization of high energy density Li-ion batteries. However, extensive volume expansion and poor cycle stability of silicon compromise its actual use. In an effort to tame volume expansion and structural disintegration during cycling, an innovative 3D electrode assembly is fabricated involving continuous layer of graphene coated on porous current collector and Si nanoparticles sealed in as an active material. Graphene deposition and pore formation in metal current collector is achieved in a unique single step synthesis. All the active components like current collector, reacting material, and conducting material are manipulated in a way to produce synergistic architecture in a chemical vapor deposition process. Highly pure graphene deposited in this process enables efficient electron transfer from allover of the surface of silicon nanoparticles and prevents continuous solid electrolyte interphase layer formation. This binder free anode assembly shows extremely stable lithium storage performance for over 1000 cycles with 88% of initial capacity retention and 100% Coulombic efficiency.

One of the most promising materials for fabricating cold cathodes for next generation high-performance flat panel devices is carbon nanotubes (CNTs). For this purpose, CNTs grown on metallic substrates are used to minimize contact resistance. In this report, we compare properties and field emission performance of CNTs grown via water assisted chemical vapor deposition using Inconel vs silicon (Si) substrates. Carbon nanotube forests grown on Inconel substrates are superior to the ones grown on silicon; low turn-on fields (similar to 1.5 V/mu m), high current operation (similar to 100 mA/cm(2)) and very high local field amplification factors (up to similar to 7300) were demonstrated, and these parameters are most beneficial for use in vacuum microelectronic applications.

A simple and scalable method of decorating 3D-carbon nanotube (CNT) forest with metal particles has been developed. The results observed in aluminum (AI) decorated CNTs and copper (Cu) decorated CNTs on silicon (Si) and Inconel are compared with undecorated samples. A significant improvement in the field emission characteristics of the cold cathode was observed with ultralow turn on voltage (E-to similar to 0.1 V/mu m) due to decoration of CNTs with metal nanoparticles. Contact resistance between the CNTs and the substrate has also been reduced to a large extent, allowing us to get stable emission for longer duration without any current degradation, thereby providing a possibility of their use in vacuum microelectronic devices.

This chapter provides an overview of different filtration processes (Sect. 31.1) and the mechanism of nanofiltration (Sect. 31.2). In the following sections, we focus on nanofiltration based on carbon nanotube membranes. A brief introduction to carbon nanotubes and their structure and properties is given, with an emphasis on the different kinds of synthesis of membranes; their function in nanofiltration in gas–vapor transport, liquid transport, and some other filtration-like techniques for filtration of bacteria and viruses is also discussed in detail (Sect. 31.3). Finally, an outlook of future research is proposed.

Commercially available Li-ion batteries have limited thermal stabilities, with safe operation range limited to about 80 oC. Nevertheless, several industries, as aerospace, oil & gas, military and biomedical, require operations to be performed at extreme environments, with peak temperatures reaching 120-150 oC and above. The market for specialty batteries is currently dominated by primary cells, raising safety concerns, requiring extensive maintenance and limiting the power output of the energy storage units. The development of a Li-ion battery that fulfills the safety and cycle life requirements for these applications is a challenging scientific problem and a great market opportunity. The ubiquity of organic solvents in the vast majority of Li-ion cells greatly limits the temperature range, due to the volatility of the electrolyte. The use of ionic liquids has been proposed as an alternative to extend the thermal stability of batteries, but there are no thin film separators capable of offering the required mechanical stability at high temperatures. Similar problems are faced by polymer electrolytes, where volume change and thermal aging decrease cycle life of devices upon long exposure to high temperatures. While solid state ceramic electrolytes possess the desired stability at elevated temperatures, their poor interfacial and wetting properties tend to limit their use to thin film configurations. None of the electrolyte systems currently used meets the requirements for proper operation of large scale devices up to very high temperatures. To tackle this issue we developed a gel-like composite electrolyte containing hexagonal boron nitride (BN) and a solution of LiTFSI in the ionic liquid 1-methyl-1-propylpiperidinium bis(trifluormethane)sulfonimide (PP13). The BN acts as a binder, providing mechanical sustentation even at elevated temperatures, while the ionic liquid offer a medium for ion transport. The ionic conductivities ranged from 0.2 mS/cm at room temperature to 4 mS/cm at 150 oC, with an average Li-ion transference number of 0.10. The electrolyte held remarkable electrochemical stability even at 120 oC, presenting an anodic stability of 5.5 V and a reversible lithium plating/stripping behavior. Tests on a half-cell configuration using Lithium Titanate (LTO) showed negligible capacity fade for testing periods over a month at 120 oC, with high coulombic efficiencies attained. The accelerated lithiation kinetics at high temperatures allowed operation even at a high 3C rate, with great capacity retention even for 600 cycles. The half-cells were able to provide stable performance even at 150 oC, showing the superb electrochemical and thermal stability of the electrolyte system. The cells were still functional at room temperature, providing 60% of the full capacity, showing that our electrolyte system presents a record upper temperature limit for a Li-ion cell that can also operate at 25 oC. Preliminary tests on a full-cell configuration at 120 oC using LTO and Li1+xMn2O4 yielded good cyclic stability, with a capacity of 70 mAh/g and a voltage output of 2.2 V. The BN-PP13-based composite showed exciting and so far unmatched performance even at highly extreme conditions. Nevertheless, the development of a proper electrolyte system to allow high temperature operation of Li-ion batteries is just the first step of many. The level of performance required for commercial applications will only be achieved with optimization of all device components, including electrode binders and cell packaging.

Batteries for high temperature applications capable of withstanding over 60 °C are still dominated by primary cells. Conventional rechargeable energy storage technologies which have exceptional performance at ambient temperatures employ volatile electrolytes and soft separators, resulting in catastrophic failure under heat. A composite electrolyte/separator is reported that holds the key to extend the capability of Li-ion batteries to high temperatures. A stoichiometric mixture of hexagonal boron nitride, piperidinium-based ionic liquid, and a lithium salt is formulated, with ionic conductivity reaching 3 mS cm−1, electrochemical stability up to 5 V and extended thermal stability. The composite is used in combination with conventional electrodes and demonstrates to be stable for over 600 cycles at 120 °C, with a total capacity fade of less than 3%. The ease of formulation along with superior thermal and electrochemical stability of this system extends the use of Li-ion chemistries to applications beyond consumer electronics and electric vehicles.

Growth of vertically aligned carbon nanotube (CNT) forests is highly sensitive to the nature of the substrate. This constraint narrows the range of available materials to just a few oxide-based dielectrics and presents a major obstacle for applications. Using a suspended monolayer, we show here that graphene is an excellent conductive substrate for CNT forest growth. Furthermore, graphene is shown to intermediate growth on key substrates, such as Cu, Pt, and diamond, which had not previously been compatible with nanotube forest growth. We find that growth depends on the degree of crystallinity of graphene and is best on mono- or few-layer graphene. The synergistic effects of graphene are revealed by its endurance after CNT growth and low contact resistances between the nanotubes and Cu. Our results establish graphene as a unique interface that extends the class of substrate materials for CNT growth and opens up important new prospects for applications.

Conventional thin film lithium ion batteries are built on a planar design where electrode material is coated on to a conducting current collector substrate. Contact resistance between the current collector and the electrode always hinders the overall performance of the battery. In order to better utilize the electrode material, 3D current collector architectures with nanoscale roughness have been proposed which would increase the electrode-current collector surface contact area thereby significantly reducing interfacial resistance. The nanoporous current collector configuration is one of several 3D designs which have shown high potential for the development of high energy and high power microbatteries. We present here a scalable process for the synthesis of three dimensional porous metallic current collectors with conformal graphene coating on the surface. One step chemical vapor deposition technique has been used for controlled etching and simultaneous graphene growth on the surface of metals such as copper and stainless steel. The 3D structures can be directly used as a cathode in lithium ion battery as graphene has lithium intercalating capability. The structural and morphology of the current collector/electrode hybrid structures were characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS) analysis, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The contribution of 3D current collectors resulted in excellent cyclic stability and capacity compared to using conventional 2D configuration.