bluuebunny/crossref_metadata_2025 huggingface dataset:
Analytical Study of the Band GAP and Optical Characteristics of Copper Sulphide Thin Film: Experiment and Computation
Authors: Ugwu Emmanuel Ifeanyi , Okwo John , Onah Daniel Ugadu , Ekpe John Elom
Published: February 2020

In this work, the analytical study of optical properties and band gap of copper sulphide thin film were carried out comparatively using two different but related depositional techniques done at room temperature. The techniques were (a) successive ionic layer adsorption and reaction and (b) chemical bath deposition. The film was characterized with emphasis on the optical properties within the spectral range of ultraviolet -infrared region of electromagnetic spectrum, Absorption coefficient depicts a maximal value of the band gap ranging from 1.45eV to 3.33 eV. Theoretically, scalar wave equation was used to analyze the behavior of wave propagated through the copper sulphide thin film for which computation of the optical properties such spectral transmittance, reflectance were computed. The band gap of the thin film was also computed for which all the computation was carried out within the same spectral range. In the analysis, it was observed that there was no significant deviation between the band gap obtained from the two different depositional techniques and the computed band gap

  Keywords;Analytical study, copper Sulphide, optical properties, band gap, Scalar wave, deposition, computation, wave propagation.
Cellular Toxicity Assessment and Environmental Impact of Pre- and Post-CMP Nanoparticle Slurries
Authors: Kosaraju Karshak , Tarannum Mubin , Crawford Steven , Aravamudhan Shyam
Published: February 2020

Engineered Nanoparticles (ENPs) of silica, ceria and alumina are used as polishing slurries for Chemical Mechanical Planarization (CMP). However, the regulations for use and toxic levels of ENPs in slurries are yet to be established. The objective of this work is to study and compare the cellular toxicity, uptake and environmental discharge levels of the CMP nanoparticle slurries before and after the CMP process and to formulate threshold levels of toxicity, namely half maximal inhibitory concentration (IC50). IC50 value is a measure that represents the effectiveness of a substance in inhibiting 50% of specific biological/biochemical function. ENPs’ reactivity along with their cellular toxicity and uptake are largely dependent on their physicochemical characteristics. This paper will also present the correlation between physicochemical properties of ENPs and toxicity level so as to design and develop benign CMP ENPs. The current study will present a comparison between pre- and post-CMP slurries containing colloidal silica, fumed silica and ceria ENPs. Post-CMP slurry waste were generated by polishing patterned test wafers of HDP oxide and copper (MIT 864 and MIT 854) for 2, 4, 6, 8 and 10 minutes on IPEC Avanti 472 CMP tool. First, pre- and post-CMP slurries and waste were comprehensively characterized using DLS, zeta potential, BET, XRD, FTIR, Raman, SEM and TEM. Next, slurries and waste were exposed to A549 lung epithetical cell lines for 6-48 hours to determine IC50 for cytotoxicity (cell viability and membrane integrity). It was observed that colloidal and fumed silica ENPs in slurries showed dose- and time-dependent IC50 for cytotoxicity. Next, using label-free analytical techniques such as confocal Raman and ICP spectroscopy, we observed that pre- and post-CMP ceria ENPs in slurries, exhibited dose-dependent uptake in A549 cells. Lastly, we studied the waste discharge to understand the constitution and concentration of various elemental species, ions and organic materials in environmental discharge.
Fabrication of Large Scale Silver Nanowire Network By Ion Beam Irradiation
Authors: Honey Shehla , Thema F.T. , Ahmad Ishaq , Naseem Shahzad , Malik Maaza
Published: February 2020

A random two-dimensional nano-network of silver nanowires (Ag-NWs) was fabricated by MeV Hydrogen (H+) ion beam irradiation. Ag-NWs were irradiated under H+ ion beam at different fluences at room temperature. Ag-NWs network was fabricated by H+ ion beam induced coalescence of Ag-NWs at the crossing and the parallel positions. H+ ion beam induced coalescence was confirmed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Moreover, structure of Ag NWs remains stable under H+ ion beam. Threshold dose for the stability of Ag NWs structure under H+ ion beam irradiation was 5x1015 protons/cm2 at room temperature, confirmed by TEM, and XRD. Morphology also remains stable under H+ ion beam irradiation. No slicing, cutting of Ag-NWs were observed under MeV H+ ion beam irradiation. This observation is useful for using Ag-NWs based devices in upper space where protons are abandon in MeV to GeV energy ranges. The results exhibit that the formation of Ag-NWs network proceeds through three steps: ion beam induced local heating, formation of simple junctions, and the formation of large scale network. This high quality network will also be useful as a transparent electrode for optoelectronics devices.
High Resolution 3-Dimensional Chemical and Morphological Imaging of Single Li
x
FePO4 Particles
Authors: Yu Young-Sang , Shapiro David , Farmand Maryam , Kim Chunjoong , Liu Yijin , Cabana Jordi
Published: February 2020

Understanding chemical and morphological transitions within single nanoparticles of electrochemically active materials is crucial to overcome the performance limitations and degradation of batteries. Techniques that afford high chemical resolution at the nanoscale are ideally suited for this goal. Soft X-ray ptychographic microscopy combined with X-ray absorption spectroscopy (XAS) is a powerful suite which affords chemical and structural information on large volumes of material at spatial resolutions better than 5 nm.1 However, to date, this technique has been intrinsically limited to 2 dimensional observations in transmission mode, which causes complications during interpretation, especially in the case of overlapped particles, because the projection images represent an average over the X-ray penetration path within the crystals.

In this study, soft X-ray tomography combined with ptychography, developed at beamline 5.3.2.1 at the Advanced Light Source (Berkeley, CA) is applied to assess the chemical and morphological consequences of electrochemical delithiation of aggregated nano-sized lithium iron phosphate (LiFePO4) plates (Figure 1). Our work provides quantitative analysis of oxidation states in 3 dimensions at the 10 nm scale. After segmentation, statistical analysis of the chemical phase for any given individual particle was achieved, and information was extracted of the particle interior. The ability to visualize the nanoscale chemical state distribution over functional volumes will revolutionize the study of energy storage materials and enable the design of optimized morphologies for the next generation of devices.

Figure 1. 3 dimensional chemical volume rendering of Li
x
FePO4 crystals. Chemical phase information were extracted from 3 dimensional volumes collected at 708.25 eV and 710.25 eV. The red and blue areas indicate the highest content of LiFePO4 and FePO4, respectively.

1. D. A. Shapiro, Y.-S. Yu, T. Tyliszczak, J. Cabana, R. Celestre, W. Chao, K. Kaznatcheev, A. L. D. Kilcoyne, F. Maia, S. Marchesini, Y. S. Meng, T. Warwick, L. L. Yang, H. A. Padmore, Nat Photon
8, 765 (2014).

Figure 1
Development of Equivalent Circuits for Litihum-Air Battery Impedance Using Mixed and Isolated Diffusion Models
Authors: Nelson Ruben , Weatherspoon Mark H
Published: February 2020

Typically, equivalent circuit models of electrochemical impedance spectroscopy (EIS) measurements include components that describe kinetic and diffusion behavior.  Often, they may be depicted as a series combination of a charge-transfer resistance and a diffusion impedance element to represent a mixed diffusion process.  Alternatively, diffusion-independent schematics also model impedance of electrochemical systems.  Because equivalent circuit modeling is an inexact description of the electrochemical impedance, either schematic may or may not indicate a good fit of the measured spectra, depending on the parameters of the circuit components. The figure below shows the significance of a mixed diffusion circuit model versus a diffusion-independent circuit model fitting the impedance of a twice cycled lithium-air battery. An appropriate circuit model must not only fit the EIS measurement, but also consider the design of the physical system to account for possible side reactions that introduce ambiguity to the model.  To overcome the impact of model uncertainty, however, alternative analysis techniques can help to verify the model of choice, such as the graphical analysis [1].

A graphical analysis of the complex impedance add additional support for a proposed physical model and its circuit parameters.  With this method, the imaginary part of the impedance versus frequency, on the logarithmic scale, are plotted to determine the frequency ranges where the impedance is linear.  The linear portions of these plots indicate separate electrochemical processes and distributed time constants, or constant phase element (CPE) behavior, with the slope of the line being the value of the CPE coefficient, α. This is helpful in determining the most accurate fit model with reasonable results. Since the focus is on the placement of the diffusion component in the circuit model, more emphasis will be on the low frequency range, where the diffusion impedance dominates.

In this study, the impedance of a lithium-air battery is measured after various cycles, and Nyquist plot and the impedance versus frequency plot are presented.  Fitted equivalent circuit models of mixed diffusion and isolated diffusion are fitted to the Nyquist plots and are compared to the results of the graphical analysis technique. 

Acknowledgment

This work was supported by the FREEDM ERC program of the National Science Foundation under award number EEC-08212121.

Reference

[1] M. E. Orazem, N. Pebere, B. Tribollet, J. Electrochem. Soc., 153, B129 (2006).

Figure 1
Interpretation of Complex Capacitance Using Equivalent Circuit Involving Constant Phase Element
Authors: Hoshi Yoshinao , Tabei Kozue , Shitanda Isao , Itagaki Masayuki
Published: February 2020

An electrochemical impedance spectroscopy (EIS) is powerful tool to evaluate the electrochemical parameters of inside the energy conversion devices. The electric-double layer capacitance C
dl can be estimated by the curve fitting of the impedance spectrum generally. It is important to obtain the C
dl of the electrode because it is related to the surface area and structure of electrode/electrolyte interface. The performance of energy conversion devices can be investigated by the capacitance plots calculated from the impedance.
(1-5) Our group
(6) previously reported the calculations of the electrochemical impedance and complex capacitance corresponding to typical equivalent circuits involving a transmission line model (TLM) in order to determine the precise value of the C
dl of electrochemical capacitor. In the present work, theory of complex capacitance were summarized by calculations using equivalent circuits. The complex capacitance calculated by equivalent circuit involving the constant phase element (CPE) was also discussed theoretically.

References:

1. P. L. Taberna, P. Simon and J. F. Fauvarque, J. Electrochem. Soc., 150, A292 (2003).

2. J. H. Jang and S. M. Oh, J. Electrochem. Soc., 151, A571 (2004).

3. J. H. Jang, S. Yoon, B. H. Ka, Y. H. Jung and S. M. Oh, J. Electrochem. Soc., 152, A1418 (2005).

4. S. Yoon, J. H. Jang, B. H. Ka and S. M. Oh, Electrochim. Acta, 50, 2255 (2005).

5. C. Portet, P. L. Taberna, P. Simon and E. Flahaut, J. Electrochem. Soc., 153, A649 (2006).

6. M. Itagaki, S. Suzuki, I. Shitanda and K. Watanabe, Electrochemistry, 75, 649 (2007).
Using Internal Pressure Measurements to Fundamentally Understand the Aging of Lithium-Ion Batteries
Authors: Wetz David Alan , Matasso Anthony , Wong Derek Nathan
Published: February 2020

The sealed nature of lithium-ion batteries makes the in-situ study of their aging mechanisms challenging at best. Typically voltage, current, thermal, and impedance diagnostics are used to characterize cell aging mechanisms as they are cycled and post mortem analysis reveals the most compelling information however further cycling of the cells is of course prohibited. While these are promising, they do not reveal the full story. At the University of Texas at Arlington (UTA), research has been performed to evaluate how cell pressure can be used as a diagnostic to better understand cell aging mechanisms at elevated rates. The cells are punctured in an inert environment and inserted into a sealed chamber where they can be cycled while measuring their internal pressure. The studies presented here have shown a strong correspondence between capacity fade and pressure rise in LiCoO2 cells across a few different rates. These results as well as some ongoing work in which LiFePO4 cells are being studied will be presented. Analysis of the impedance growth as well as the gas generated while cycling the cells will also be discussed.
Electrolyte-Cathode Interactions
Authors: Russell Selena M. , Cresce Arthur v. , Xu Kang
Published: February 2020

As lithium-ion batteries evolve toward higher cell voltage and capacity, developing detailed knowledge of the electrolyte-electrode interface is critically important. The chemical composition and morphology of interphases dictate not only the reversibility (cycle or calendar life), but also the kinetics of the cell chemistry (power density), and it has been well-recognized that the complicated interplay among electrolyte components (solvent, salt anion, additive) and electrode surfaces affect interphasial properties. While there is general agreement on solid electrolyte interphase (SEI) formation on graphitic anodes, clear evidence of passivation at the cathode interface remains elusive. Primarily using in-situ electrochemical atomic force microscopy (EC-AFM) and confocal Raman spectroscopy, our studies focus on the in situ and in operando electrolyte-cathode interactions under various chemical and electrochemical environments with the goal of identifying factors that influence phenomena at the interface.
Effect of Anion Solvation on the Passivation Chemistry of Lithium Ion Electrodes
Authors: Cresce Arthur v. , Russell Selena M. , Xu Kang
Published: February 2020

Ion solvation in electrolytes is a key issue in the understanding of interfacial behavior in lithium ion batteries. It has been shown experimentally that the solvation of Li+ in binary electrolyte solutions directly influences the formation of the solid electrolyte interphase (SEI) layer at the surface of graphitic anodes, and likely other types of anodes as well. Anions in lithium salt systems, especially the important anion PF6
-, exhibit specific solvent preferences as well, though PF6
- and comparable anions (BF4
-, TFSI-, FSI-, ClO4
-) do not form strong or long-lasting interactions with solvent molecules. This talk will explore new evidence of anion-solvent interactions, and will summarize efforts to link anion solvation to cathode SEI formation. Passivation of cathode interfaces with SEI is an important topic, as cathodes are increasingly reaching higher oxidation potentials that cause degradation of electrolytes. New, higher-voltage lithium ion batteries will be limited by development and understanding of oxidation behavior at the cathode-electrolyte interface.
Electrochemical Charge Transfer Reaction Kinetics at Silicon Electrode Surfaces
Authors: Swamy Tushar , Chiang Yet-Ming
Published: February 2020

The volumetric lithiation capacity of silicon as an anode material is roughly ten times that of conventional graphite, while their densities are comparable. As a consequence, for a given particle size and C-rate, the current density required to cycle a silicon electrode at a given C-rate is about ten times greater than that of graphite. Such high current densities may cause the charge transfer kinetics at the silicon electrode surface to become rate limiting during use, depending on the magnitude of the corresponding Butler-Volmer exchange current density.  

Further motivated by the lack of consensus in the literature [1-4], we developed a novel approach to measure the exchange current density, using single crystal electronically conductive silicon wafers with well-defined crystallographic (100) orientation and active areas, and a cycling scheme to avoid stress-induced surface cracking and fragmentation upon lithiation. Electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy were used as characterization tools. It was demonstrated that the silicon electrode surface remains crack free during the first lithiation half cycle, with fracture being induced only during the following delithiation half cycle, which is in agreement with the observations made by Chon et al. [5]. Consequently, it was possible to grow the solid electrolyte interface (SEI) layer as is characteristic of silicon powder electrodes, while still using the geometric area as the electrochemically active surface area to evaluate the surface kinetic parameters from EIS experiments.

The exchange current density at the silicon electrode surface was found to be 0.1 ± 0.01 mA/cm2 for electrolyte consisting of 1 M LiPF6 in EC/DMC (1/1)w + FEC (10%)w + VC (2%)w. Figure 1 shows the corresponding kinetic overpotential as a function of particle diameter and C-rate for silicon and graphite. Clearly, the overpotential is much greater in the silicon case. The impact of these results on cell performance is discussed. The measured exchange current density values may be used as input for porous electrode models, and to devise electrode microstructures and cycling regimes for improved fracture tolerance and overall performance.

Acknowledgments

This work was supported as part of the NorthEast Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012583.

References

[1] L. Baggetto et al., J. Power Sources, 189, 402–410 (2009)

[2] L. Baggetto, R. A. H. Niessen, and P. H. L. Notten, Electrochim. Acta, 54, 5937–5941 (2009)

[3] V. A. Sethuraman, V. Srinivasan, and J. Newman, J. Electrochem. Soc., 160, A394–A403 (2013)

[4] R. Chandrasekaran, A. Magasinski, G. Yushin, and T. F. Fuller, J. Electrochem. Soc., 157, A1139 (2010)

[5] M. J. Chon, V. A. Sethuraman, a. McCormick, V. Srinivasan, and P. R. Guduru, Phys. Rev. Lett., 107, 045503 (2011)

Figure 1
(Invited) Insight into Bulk and Interfacial Structure of Electrolytes and SEI Components from Molecular Modeling
Authors: Borodin Oleg , Olguin Marco , Henderson Wesley A
Published: February 2020

Obtaining fundamental understanding and ultimately controlling bulk and interfacial properties of battery electrolytes is important for increasing battery power and energy density. Molecular dynamics simulations using many-body polarizable APPLE&P force field and ab initio Born Oppenheimer Molecular Dynamics (BOMD) simulations were used to examine the relationship between the structure of lithium solvates and ion transport in a wide range of electrolytes with potential applications in lithium battery. The solvate structures are systematically examined for electrolytes doped with LiFSI, LiTFSI, LiTriflate, LiPF6 and other salts in multiple solvents. Structural properties of SEI compounds will be also discussed. Previously reported1 interfacial properties for the dilithium ethylene dicarbonate (Li2EDC) – electrolyte interface will be contrasted with the interfacial properties for the Li2EDC – LiF interface. Transport mechanism including grain-boudary diffusion in the Li2EDC – LiF composite will be discussed.

References

 1. O. Borodin, in Electrolytes for Lithium and Lithium-Ion Batteries, T. R. Jow, K. Xu, O. Borodin and M. Ue Editors, p. 371, Springer New York (2014).
(Invited) Expanding Electrochemical Stability Window of Electrolytes
Authors: Xu Kang , Cresce Arthur v. , Russell Selena M. , Wang Chunsheng
Published: February 2020

As the essential component in any energy storage device, electrolyte determines a number of key performances of the device, including temperature range for service, rate of electrochemical reaction, safety under both normal and abusive operations, cycle/calendar life as well as the maximum voltage and capacity allowed. Among these, the electrochemical stability window is perhaps the most intriguing property, because in almost all electrochemical devices, the electrodes operate at potentials far beyond what thermodynamics allowed. This group at ARL has been trying to understand this basic phenomenon and exploring various means to affect the surface chemistry at electrode/electrolyte junctions, so that this stability window could be expanded. This talk will summarize these recent efforts.
Controlled Release of Encapsulated Additives for Enhanced Performance of Lithium-Ion Batteries
Authors: Lim Taewook , White Scott R. , Sottos Nancy R.
Published: February 2020

Autonomous strategies are developed for controlled release of encapsulated vinylene carbonate (VC) to promote beneficial interfacial reactions for SEI (Solid-Electrolyte Interphase) formation. Typically, VC is incorporated in a lithium-ion battery when it is manufactured but its initial concentration is usually limited to a maximum of a few wt% to avoid increased cell resistance due to a reaction of surplus VC. This initial concentration of VC is rapidly consumed during the initial charge and discharge cycles and cannot be utilized effectively for subsequent cycles. In our approach, microcapsules containing VC additive are designed for release of the additive into electrolyte over time. The diffusion-based release of VC from the microcapsules into electrolyte leads to a relatively low VC concentration during initial charge and discharge cycles, and additional VC is available for subsequent cycles.

The VC microcapsules are successfully prepared by a solvent-exchange method that allows VC to diffuse through the microcapsule shell-wall at elevated temperature. VC concentration profiles in electrolyte at three different environments (pouch cell with 2wt% VC, pouch cell with 5wt% VC microcapsules, and electrolyte with 5wt% VC microcapsules) were evaluated at room temperature by taking aliquots of electrolyte at fixed intervals and measuring the VC concentration by NMR. In pouch cells where 2wt% VC liquid was added directly to electrolyte (not encapsulated), the VC concentration decreased significantly after the first cycle at C/10 rate. In great contrast, in pouch cells that contained VC microcapsules, the VC concentration increased from 0 to 3wt% due to timed-release of encapsulated VC in electrolyte.

To evaluate the electrochemical performance for the additive release from microcapsules, we conducted EIS (Electrochemical Impedance Spectroscopy), cycling tests at various C-rates, as well as long-term cycling tests for pouch cells containing no VC (0wt%), VC liquid (5wt% not encapsulated) and VC microcapsules (5wt%). Comparison of the impedance spectra (Fig. 1a) showed that interfacial resistance for pouch cells with 5wt% VC microcapsules was much lower than pouch cells with same amount of VC liquid added directly, which results from lower initial VC concentration in pouch cell with VC microcapsules. In cycling tests at various C-rates, the pouch cell with 5wt% VC microcapsules has even better rate capability, where its discharge capacity was over 2.5 times higher at 5C-rate compared to pouch cell with 5wt% VC liquid. After 400 cycles at 1C-rate (Fig. 1b), the pouch cell with VC microcapsules showed similar capacity retention as the pouch cell including same amount of VC liquid (not encapsulated). This result provides preliminary evidence that the rate capability of lithium-ion batteries can be enhanced without trade-off for capacity retention through time release of microencapsulated additives.

Figure 1
Lithium-Ion Polymer Batteries Assembled with a Cross-Linked Composite Polymer Electrolyte Using a Vinyl-Functionalized SiO2 Nanoparticles
Authors: Shin Won-Kyung , Cho Jinhyun , Yoo Ji-Hyun , Lee Yoon-sung , Kim Dong-Won
Published: February 2020

Recently, a safety of lithium-ion batteries has been a critical issue as the demand of high capacity batteries for electric vehicles and energy storage systems has increased.  The electrolyte commonly used in current lithium-ion batteries is lithium salts (mostly LiPF6) in a mixture of carbonate-based organic solvents.  However, the high flammability of the organic solvents in liquid electrolyte can lead to fires and explosions when short circuits or local overheating accidentally occurs [1].  Furthermore, HF can be generated by thermal decomposition and hydrolysis of LiPF6 by trace moisture in the electrolyte solution, which leads to degradation of the cycling performance of lithium-ion batteries at high temperature [2, 3].  Among the various electrolyte systems for lithium-ion batteries, the cross-linked polymer electrolyte is one of the promising candidates due to its high ionic conductivity, good interfacial properties and thermal safety with no electrolyte leakage.  In this work, we synthesized the vinyl-functionalized SiO2 particles and coated them onto the fibrous polymer membrane or the microporous polyolefin separator.  The SiO2 particles on polymer participated in free radical polymerization with tri(ethylene glycol) diacrylate in a gel electrolyte precursor to form a cross-linked composite polymer electrolyte.  An in-situ cross-linking reaction using these reactive SiO2-coated separators promoted strong interfacial adhesion between electrodes and separator, and allowed effective encapsulation of liquid electrolyte, resulting in low interfacial resistances.  In addition, the silica nanoparticles played a role as HF scavengers to reduce HF content in the electrolyte at high temperature.  The lithium-ion polymer cells assembled with a SiO2-coated separator exhibited superior cycling performance to cell prepared with a conventional polyethylene separator due to the strong interfacial adhesion between the electrodes and separator, as well as suppression of deleterious reactions during cycling.

References

1.  J.Wen, Y.Yu, C.Chen, Mater. Express, 2, 197 (2012).

2. E.Zinigrad, L.Larush-Asraf, J.S.Gnanaraj, M.Sprecher, D.Aurbach, Thermochim Acta, 438, 184 (2005).

3. S.F.Lux, I.T.Lucas, E.Pollak, S.Passerini, M.Winter, R.Kostecki, Electrochem. Commun., 14, 47 (2012).
A Novel Class of All Inorganic Solid State Lithium Ion Conductors
Authors: Klein Iolanda Santana , Davidowski Stephen Kyle , Angell Charles Austen
Published: February 2020

Most commercial lithium batteries use electrolytes that are organic solutions of lithium salts, the classic example being the lithium hexafluorophosphate (LiPF6). Although those electrolytes satisfy the requirements of high conductivity and practical chemical window, there are numerous safety issues (including leakage and flammability) that call for alternative materials. In this work, we present a novel class of all inorganic, solid state lithium-ion conductors with very high conductivities (on the order of 6 mS.cm-1 at room temperature) made from inexpensive materials. The new materials are rotator phases in which lithium is the most mobile species. The all inorganic nature of the new compounds result in a higher operating temperature range than that achieved when organic solvents are used, and the new materials retain competitive conductivities even at very low temperatures (46 µS.cm-1 at -30oC). The new materials were characterized by magic angle spinning solid-state nuclear magnetic resonance (MAS NMR), Raman spectroscopy, powder X-ray diffraction, differential scanning calorimetry and electrochemical impedance spectroscopy (EIS).
Exceptionally Stable, Non-Aqueous, Sodium-Based Electrolytes for High Energy Electrochemical Capacitors
Authors: Sun Che-Nan , Ruther Rose Emily , Delnick Frank , Nanda Jagjit
Published: February 2020

Current-generation, acetonitrile-based electrolytes for supercapacitors have a practical voltage window around only 2.7 V. Extending the electrochemical window can significantly increase energy density, since the energy stored in a capacitor increases quadratically with voltage. We report on electrolytes consisting of sodium salts in linear polyether (glyme) solvents which clearly show a 4 V electrochemical window. Electrolyte conductivities range between 1-10 mS/cm, which are comparable to ionic liquids or propylene carbonate-based electrolytes.  Importantly, all salts and solvents are commercially available. This family of electrolytes has the potential to double the energy density of supercapacitors, while remaining as cost-effective and scalable as today’s commercial electrolytes.

Acknowledgement

This work is supported by Laboratory Directed Research and Development (LDRD) program of Oak Ridge National Laboratory under the seed project S12-056.
Determining the Transport Properties of Electrolyte Solutions By in-Situ NMR Imaging and Inverse Modeling
Authors: Halalay Ion C. , Sethurajan Athinthra K. , Protas Bartosz , Krachkovskiy Sergey , Goward Gillian
Published: February 2020

We used NMR imaging (MRI) combined with a data analysis by modeling of the inverse mass transport problem, to determine salt diffusion coefficients D+
and transference numbers t+
in electrolyte solutions of interest for Li-ion batteries. Sensitivity analyses have shown that accurate estimates of these parameters (as a function of concentration) are critical to the reliability of the predictions provided by models of porous electrodes. The inverse modeling (IM) solution was generated with an extension of the Planck-Nernst model for the transport of ionic species in electrolyte solutions. Concentration dependent diffusion coefficients and transference numbers were derived using concentration profiles obtained from in-situ 19F MRI measurements. Material properties were reconstructed with minimal assumptions, using methods of variational optimization to minimize the least-square deviation between experimental and simulated concentration values. Diffusion coefficients obtained by pulsed field gradient NMR (PFG NMR) fall within the 95% confidence bounds for the diffusion coefficient values obtained by the MRI+IM method. This demonstrates that PFG NMR determines chemical (Fickian) diffusion coefficients in concentrated electrolyte solutions and not self-diffusion coefficients. The MRI+IM method also yields the concentration dependence of the Li+transference number in agreement with trends obtained by electrochemical methods for similar systems and with predictions of theoretical models for concentrated electrolyte solutions, in marked contrast to the salt concentration dependence of transport numbers determined from PFG NMR data.

Acknowledgements

The authors acknowledge funding through the NSERC APC program and GM of Canada.

Figure 1
Degradation Behavior in Lithium Iron Phosphate Secondary Cells Under High Rate Pulsed Discharge
Authors: Wetz David Alan , Wong Derek Nathan
Published: February 2020

LiFePO4 secondary cells cycled under a ultra-high rate pulsed discharge profile are dismantled to study the changes in surface chemistry in pulse power load systems. Three cells lost the ability to charge (0 Ahrs) in less than 50 cycles at 15C (40A) pulsed discharge/continuous recharge conditions. Electrode samples show varying levels of solid electrolyte interphase growth. However, x-ray absorption near edge structure analysis conducted on the cathode material shows minimal loss of active lithium. A cell cycled under the same conditions with a 60°C operating temperature limit showed more gradual capacity fade and a higher degree of shift in the photon energy of the XANES spectrum. XPS analysis shows thicker SEI formation in the 60°cells. This indicates that the additional thermal energy in the 75°C cells provide more favorable conditions for the evolution of a degradation mechanism that is more complex than lost active material. Increased concentration in oxygen at the anode surface indicates heavy reduction in the electrolyte salt forming LixPFy-Oz. The 0 Ahr cells showed higher concentration of Fluorine and an SEI that contains mostly LiF. Results suggests that high temperature, ultra-high rate pulsed cycling favors LiPF6 reduction into LiF and thus the concentration of Li2CO3 in the SEI is reduced creating a high impedance film.
Complementary Operando Investigations of Graphite Cycled in Ionic Liquids By XPS and Raman Spectroscopy
Authors: Streich Daniel , Novák Petr , El Kazzi Mario
Published: February 2020

Stable electrochemical cycling of graphite in ionic liquid electrolytes has recently been achieved in  presence of bis(fluorosulfonyl)imide ([FSI]-) [1]. To get a better understanding of how FSI enables stable cycling, Raman spectroscopy (Raman) [2] and x-ray photoelectron spectroscopy (XPS) [3] were employed as two complementary operando techniques to monitor changes in the bulk structure and the chemical surface composition of graphite particle and HOPG model electrodes, respectively. These electrodes were cycled in 1-ethyl-3-methylimidazolium / bis(trifluoromethanesulfonyl)imide ([EMIM][TFSI] ionic liquid electrolyte containing either 1 M LiTFSI or 1 M LiFSI salt. The Raman experiments show that [EMIM]+ strongly competes with Li+ for intercalation sites in graphite and that Li+ intercalation only takes place at a detectable level in presence of [FSI]- (Figure 1.a). XPS at the IL/electrode interface suggests that both [TFSI]- and [EMIM]+ undergo reductive decomposition reactions resulting in the formation of a solid surface layer (Figure 1.b). A model describing the mechanism behind the cycling improvement in presence of FSI- will be presented based on these results.

[1] M. Ishikawa, et al, Journal of Power Sources
162, 658-662 (2006)

[2] P. Lanz, P. Novák, J. Electrochem.
Soc. 161, 10, A1555-A1563 (2014)

[3] D. Weingarth, A. Foelske-Schmitz, A. Wokaun, R. Kötz, Electrochem. Commun. 11, 619-622 (2011)

Figure 1
Elucidating the Interfacial Structure at the Ionic Liquid-Solid Interface Using Atomic Force Microscopy and Molecular Dynamics
Authors: Black Jennifer , Feng Guang , Zhang Yu , Okatan M. Baris , Zhang Pengfei , Dai Sheng , Kalinin Sergei V. , Cummings Peter T , Balke Nina
Published: February 2020

The structure and properties of ionic liquids (ILs) at the solid-liquid interface will govern their performance in all applications including energy storage and catalysis. Although it is well known that the interfacial structure of ionic liquids is very different to that of classical dilute electrolytes, a comprehensive understanding of the ion structure within the electrical double layer for this class of electrolytes is still lacking.  Therefore it is necessary to have experimental methods to elucidate the interfacial ion structure which can be related to electrochemical performance. Atomic force microscopy (AFM) force spectroscopy is capable of probing the layered ion structure formed at the interface, and offers advantages over other techniques (e.g. x-ray and neutron reflectivity, surface force apparatus) due to its high spatial resolution allowing for the ion structure to be examined in a spatially resolved manner. Although there are several studies demonstrating the impressive ability of AFM to probe the interfacial ion structure in ionic liquids, several questions remain regarding the measured AFM response. (e.g. what is the role of the AFM probe?, Do we measure cations or anions? Can we tune ion selectivity?)

In this work we examine the AFM force profiles of various ionic liquids at different substrates to examine how the substrate and ionic liquid properties affect the interfacial ion structure. We also use a series of different AFM probes of different geometry and chemistry to determine the effect on the measured force profiles. Our experimental results are compared directly with molecular dynamics simulations, and through a combination of experimental and theoretical approaches we are able to develop a better understanding of the measured force response and factors determining the interfacial structure at the ion-liquid solid interface.
High Capacity Li-Rich Cathode Materials
Authors: Luo Kun , Roberts Matthew , Hao Rong , Bruce Peter G
Published: February 2020

The need for better batteries has never been greater. Many automotive manufacturers now believe that limitations in the performance of current lithium-ion batteries represent the greatest barrier to the electrification of transport. Lithium batteries may also play a critical role in de-carbonization of the electricity grid.

Lithium rich layered cathodes, which offer increased capacity, have, for several years, been regarded as the next major advance, but they are still challenged by problems such irreversible first cycle capacity, voltage fade on cycling related to changes in the structure. Recently important work has been carried out to better understand the origin of the high capacity and the voltage fade.

In this contribution we shall present a new sol-gel synthesis for compositions such as Li1.2Mn0.54Ni0.13Co0.13O2 and discuss their limitations and operation. In addition the mechanisms of charge compensation, oxygen loss vs oxygen redox, will be considered. The electrochemical performance is shown in Figure 1. The characteristic load cure is seen with a significant first cycle irreversible capacity; the implications of this will be discussed. The cycling stability of the material is good with a capacity of ~250 mAh g-1 maintained after 100 cycles.

Figure 1
Charging Voltage Limit Effects on the Electro-Chemical Behavior of High Capacity Manganese-Rich Cathode in Lithium Ion Batteries
Authors: Mao Wen-feng , Fu Yanbao , Ai Guo , Battaglia Vince
Published: February 2020

Compared with normal cathode materials for lithium ion batteries (LIBs) (such as LiCoO2, LiMn2O4, Li[Ni1/3Co1/3Mn1/3]O2 and LiFePO4), the high capacity manganese rich cathode (HCMR) materials (xLi2MnO3• (1-x)LiMO2, M = Ni, Co, Mn) demonstrates the highest discharge capacity (~250 mAh g-1) along with cost reduction and safety enhancement. This material is therefore considered as a high promising cathode material for the next generation LIBs. However, the charging voltage limits effects on the electrochemical behavior have never been studied. And this material presents complex structural changes upon cycling that are still misunderstood. The purpose of this study is to investigate the charging voltage limit effects on the electrochemical performance and structure of HCMR cathode material.

HCMR electrodes were prepared with a composition of active material (85 wt%), acetylene black conductive additive (7%), and PVdF binder (8%).  The loading is about 1.0 mAh/cm2. 2325 coin cells were assembled for electrochemical measurement with Celgard 2400 as separator and lithium metal as counter electrode. Electrochemical measurements were performed using a Maccor battery cycler.

The charge-discharge curves and corresponding cycling performances between 2.0 V and five different upper voltage limits are shown in Fig. 1 and Fig. 2. There is an obvious voltage plateau around 4.5 V during the first charge process, which may be responsible for the activation of the HCMR. The capacities of this material improved with an increase in upper voltage limit up to 4.8 V. For the upper voltage limit of 4.5 V, the capacity of HCMR increased for the first 60 cycles, which may be related to the gradual activation of the HCMR. When the upper voltage exceeds 4.8 V, electrolyte oxidation involving the cathode is believed to cause an increase in resistance that and worse capacity retention. Considering both the discharge capacity and capacity retention, 4.7 V seems to be the best charging voltage limit, which exhibits a discharge capacity of ~240 mAh g-1and capacity retention of 99.88% after 350 cycles. It is well known that the voltage decreases with cycling. The dQ/dV curves (Fig. 3) indicate that both peak voltage and peak area, which are highly related to the HCMR structure and electrochemical performance, change with cycling and upper voltage limit.

Although an increase in the upper voltage limit can improve capacity, 4.7 V is the best upper cut-off voltage for long life and high energy LIBs containing HCMR. The structure changes will be discussed in further work.

Figure 1
Origins of the DC-Resistance Increase in HCMRTM Cathodes
Authors: Kostecki Robert , Battaglia Vince , Chen Guoying , Chen Wei , Liu Gao , Membreno Daniel , Persson Kristin A , Shukla Alpesh Khushalchand , Terborg Lydia , Yi Tanghong
Published: February 2020

High capacity manganese rich (HCMR™) materials are promising candidates for commercial Li-ion battery positive electrodes for applications in electric and plug-in hybrid electric vehicles.1 These oxides, also denoted as xLiMO2 - (1-x)LiMnO3 (M = Co, Mn, Ni), deliver a high discharge capacity (>240 mAh/g) at operating voltages exceeding 3.5 V vs. Li/Li+.2 However, these materials have significant limitations and suffer from high first cycle irreversible capacity loss, impedance rise and voltage fade during cycling.2-4 Extensive studies of HCMR™ electrodes indicated a structural modification/ rearrangement as one of the major reasons for the electrode/material degradation.

In this work three possible scenarios for the origin of the DC-R rise are presented:

Evidence of Structural Transformation with Cycling and Proposed Strategies Using Lithium and Transition Metal Substitutions

In this section first-principle studies of the structural stability of Li2-xAx(Mn1-yBy)O3 and the effect of doping as well as the structure and possible structural changes of the pristine and aged HTMRTM material are discussed. Preliminary evaluations of the material suggest a single phase, aperiodic crystal consisting of monoclinic domains.

Ionic and Electronic Barriers at Interphases and Interfaces

In situ Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and potentiostatic intermittent titration technique (PITT) provide information about structural changes of the surface, surface layer formation and Li+ diffusivity.  Raman spectroscopy suggests transformation to a spinel like structure and FTIR spectroscopy indicates formation of a surface film composed of electrolyte decomposition products. The Li+ diffusivity in HCMRTM correlates strongly with the DC-R behavior within each cycle.

Loss of Mechanical Integrity in HCMRTM Material - Changes in Morphology and Topology

Discussion of how changes in morphology and topology during cycling correlate with long term impedance rise and changes in the unit cell parameters of the HCMRTM material.

Acknowledgements

This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, under the Applied Battery Research for Transportation (ABR) Program and Award Number DE-EE0006443.

References

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2.  Y. Li, M. Bettge, B. Polzin, Y. Zhu, M. Balasubramanian and D. P. Abraham, J. Electrochem. Soc., 160, A3006 (2013).

3.  K. J. Carroll, D. Qian, C. Fell, S. Calvin, G. M. Veith, M. F. Chi, L. Baggetto and Y. S. Meng, Phys Chem Chem Phys, 15, 11128 (2013).

4.  D. Mohanty, A. S. Sefat, S. Kalnaus, J. L. Li, R. A. Meisner, E. A. Payzant, D. P. Abraham, D. L. Wood and C. Daniel, J Mater Chem A, 1, 6249 (2013).
(Invited) Advances in Cathode Materials for High Energy Density Lithium-Ion Batteries
Authors: Nanda Jagjit
Published: February 2020

Advances in high energy density of lithium-ion technology hinges upon the development of next generation high capacity cathode materials. Current state-of-the-art cathodes like NMC have capacity in the range of 180 mAh/g within a voltage window of 2.5-4.2 V. This is a factor of two less than the capacity of the most commonly used anode material, carbon (372 mAh/g). Current high voltage cathode chemistries such as lithium-manganese rich NMC (LMR-NMC) cathodes though promise capacities > 270 mAh/g when cycled to 4.7 V but has a number of stability issues including phase transition and TM dissolution.  Mn-Ni high voltage spinel although structurally stable and more robust has relatively lower capacity 147 mAh/g.  More than anything these high voltage cathodes need to be cycled at voltages > 4.6 volts that is clearly above the electrochemical stability window for the most commonly used electrolytes (LiPF6 in carbonates). 

The talk will review the research progress made in the area of high voltage cathodes for lithium-ion namely, lithium-magnanese rich NMC and high voltage spinel, and the remaining challenges there-in. Topics include other alternative high capacity, 4 V cathodes chemistries that utilize multiple redox states of the host transition metals and thereby intercalate two or more lithium ions per formula unit of the TM.  To this effect, we report our recent work on solid-solution compositions of nickel-stabilized two lithium copper oxides having generic formula, Li2CuxNi1-xO2, where x = 0.4-0.6. Optimized composition of this family of cathodes show reversible capacities in excess of 200 mAh/g with good capacity retention but further work is needed to stablize the structure.
Synthesis of LiCoO2 and LiNi1/3Mn1/3Co1/3O2 2D Nanosheets By Osmotic Swelling for High Performance Lithium-Ion Batteries
Authors: Cheng Qian , Chan Candace K.
Published: February 2020

2D materials have attracted a great deal of attention for their unique electrical and magnetic properties, but may also play important roles in energy storage applications. Lithium-ion batteries and supercapacitors are widely used to power mobile devices, but the energy and power densities of the electrode materials still need improvement. Many conventional battery materials have layered structures, and hence can be readily exfoliated into 2D nanosheet materials.  The high surface area and short ionic diffusion distances in the 2D nanosheets may improve the charging/discharging rates and result in more lithium insertion or surface adsorption. Furthermore, hybrid electrode materials composed layers of different cathode materials may be possible by reassembling different nanosheets. These sandwich structures could potentially result in unique synergistic effects and novel redox behavior due to the interactions from different sheets. Finally, we can obtain better understanding of the structure of complex layered cathode materials through exfoliation and high resolution ex-situ microscopy studies.

Here we present our synthesis of 2D nanosheets of two common lithium-ion battery materials, LiCoO2 (LCO) and LiNi1/3Mn1/3Co1/3O2 (NMC). Nanosheets were obtained by exfoliation of LCO and NMC particles using traditional osmotic swelling with tetraethylammonium (TEA). TEM, SEM and AFM analysis showed that the particles were successfully exfoliated nanosheets with around 2 nm thickness. XRD and SADP[CKC1]  analysis showed that these materials had hexagonal structures with good crystallization. A reassembly process was developed and applied to obtain LCO, NMC, and LCO/NMC hybrid particles. Electrochemical evaluation of the particles as electrodes for lithium-ion batteries and supercapacitors were performed. Our work is a firm step forward on improving understanding of osmotic swelling processes for the synthesis of nanosheets from complex metal oxides as well as the design and fabrication of high performance hybrid electrodes for energy storage applications.