bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) P-Type Transparent Conducting Oxide Protection Layers for Sustainable Photoelectrochemical Water Oxidation
Authors: Chen Le , Yang Jinhui , Lee Lyman , Klaus Shannon , Woods-Robinson Rachel , Lum Yanwei , Cooper Jason K. , Sharp Ian D. , Bell Alexis T. , Ager Joel W.
Published: February 2020

Achieving stable operation of high efficiency photoanodes used as components of solar water splitting devices is critical to realizing the promise of this renewable energy technology.  Here, we show that a p-type transparent conducting oxide (p-TCO) can function as a selective hole conduct and corrosion protection layer on photoanodes used for light-driven water oxidation. We selected NiCo2O4 with the inverse spinel structure was used as the p-TCO and show that this material, when integrated with Si-based photoanodes, has the requisite electronic structure, stability, transparency, and hole conductivity to achieve sustained and efficient solar water oxidation. 

NiCo2O4 was deposited on n-Si (100) and np-Si (100) by reactive sputtering at a substrate temperature of 70-100 °C.  The film structure was amorphous, as shown by the lack of XRD and Raman features. P-type conductivity was confirmed by measurement of a positive Seebeck coefficient. Light transparency of >70% (l > 400 nm) was achieved with a NiCo2O4 thickness of 40 nm.  The hole conductivity was 50-60 S/cm and, as expected, p-NiCo2O4 forms a rectifying contact to n-Si. 

Photoelectrochemical (PEC) evaluation was performed in aqueous 1M NaOH (pH 14) with simulated AM1.5 illumination; these conditions would rapidly corrode the n-Si photoanodes in the absence of a protection layer.  PEC performance of the np-Si/p-NiCo2O4 structures is excellent, particularly when a thin NiFe oxygen evolving catalyst is applied.  An onset potential of 0.95 V vs. RHE is observed, which is one of the lowest reported for a Si-based photoanode.  The current density at the reversible potential for water oxidation (+1.23 V vs. RHE) is >25 mA cm-2, and the current rises to a limiting value of 30 mA cm-2 at more anodic potentials, which demonstrates the attractive combination of transparency and low-resistance hole conductivity in the NiCo2O4.  Long-term testing indicates multi-day stability with minimal decrease in performance or observable corrosion of the Si photoanode.  In depth characterization of both the solid-solid interfaces between NiCo2O4 and light absorber/catalyst and of the solid/electrolyte interface will be discussed. 

This work demonstrates that p-TCOs are promising as corrosion protection layers for stable water oxidation photoanodes.  

This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993.
(Invited) Exploration of Structure-Function Relationships for Electrocatalytic Water Oxidation By Molecular [Mn12O12] Clusters
Authors: Yan Yong
Published: February 2020

Abstract: A series of Mn12O12(OAc)16-xLx(H2O)4 molecular clusters (L = benzoate, benzenesulfonate, diphenylphosphonate, dichloroacetate) were electrocatalytically investigated as water oxidation catalysts on an FTO glass electrode. Four of the compounds demonstrated water oxidation activity at pH 7.0 at varying overpotentials (640–820 mV at 0.2 mA/cm2) and with high Faradaic efficiency (85–93%). For the most active complex (L = diphenylphosphine), more than 200 turnovers were observed after 5 min. A known water oxidation catalyst Mn4O4L6 (L=diphenylphoshine) was also explored and compared under the same electrochemical profile. Two structure-function relationships for these complexes were developed. First, these complexes must undergo at least 1-electron oxidation to become active catalysts, and complexes that cannot be oxidized in this potential window were inactive. Second, a greater degree of distortion at cubane-like Mn1 and aqua-ligated Mn3 centers correlated with higher catalytic activity. From this distortion analysis, either or both of these two Mn centers are proposed to be the catalytically active site. Finally, these findings support utilization of cluster complexes as models for oxide-based catalysts to investigate key structural features, and to extend this approach towards the elucidation of catalytic mechanisms and intermediates to aid the design of next-generation oxide catalysts.
(Invited) Investigations into the Formation of Germanene Using Electrochemical Atomic Layer Deposition (E-ALD)
Authors: Ledina Maria , Liang Xuehai , Kim Youn-Geun , Jung Jin , Perdue Brian , Tsang Chu , Soriaga Manuel , Stickney John Lewellen
Published: February 2020

Germanene would be the Ge analogue of Graphene.   A number of ab-initio calculations in the literature suggest that Germanene sheets would display unique properties, similar to those observed in Graphene.  Those reports indicate the deposits should have a buckled structure, where half the atoms are about 0.7 nm higher than the other half.   MicroRaman, electrochemistry and in-situ scanning tunnelling microscopy (EC-STM) have been used to better understand the electrochemical growth of Ge from aqueous solutions, from the first atomic layers on Au(111).    The studies to be discussed have resulted in some interesting, though not clearly understood results, such as why only about 3 ML of Ge can be formed by direct electrodeposition on Au, depending on the pH. Subsequent deposition, under those aqueous conditions, simply stopped after three ML. Reports in the literature indicate that thicker deposits of Ge can be formed on other electrode surfaces, though it is not clear why growth on Au is different.  In-situ STM studies of the first atomic layers of Ge have shown a number of processes which are not yet well understood, such as the formation of nanoscopic atomically flat chips on the surface.  There are suggestions that Germanene is being formed.  In addition, there is clear evidence of the formation of a surface alloy with the Au substrate, though the phase diagram suggests no significant alloying at room temperature, used in these studies.  Further, though Au(111) displays the expected reconstructed (√3X23) “herringbone” structure expected, incorporation of Ge into the this structure occurs very slowly by reduction at relatively high potentials, starting at defects and step edges.  Previous work by this group, lead to development of an electrochemical ALD cycle for the growth of thicker Ge films.   That cycle is being further investigated, as some spots in early deposits displayed a Raman spectrum indicative of the presence of germanene.
A Study on the Seed Step-Coverage Enhancement Process (SSEP) of through Silicon Via (TSV) Using Electrophoretic Deposition (EPD) of Pd/PVP Colloids
Authors: Lee Dongryul , Lee Yujin , Cho Hyungkoun , Lee Min Hyung
Published: February 2020

The seed step-coverage enhancement process (SSEP) using Pd/PVP (Polyvinylpyrrolidone) colloids were investigated for the filling of through silicon via (TSV) without void. TEM analysis showed that the Pd nano-particles were well dispersed in aqueous colloidal solution with average diameter of 5.67 nm. These Pd nano-particles were uniformly deposited on the substrate of Si/SiO2/Ti wafer by electrophoresis with high frequency alternating current (AC). After electroless Cu deposition on the substrate treated with Pd/PVP colloids, the adhesive property between deposited Cu layer and substrate was evaluated. As a result of that, the Cu deposit showed superior adhesion property in comparison with that on treated substrate by the existing Pd ion catalyst. Finally, by implementing the SSEP using Pd/PVP colloids in TSV, we achieved 700% improvement of step coverage of Cu seed layer compared to PVD process, resulting in void-free fillng in high aspect ratio TSV.
Mechanistic Transition of Electron Transfer Kinetics from Quantum Electron Tunneling to Trap-Facilitated Hopping through TiO2 Films Grown By Atomic Layer Deposition on SnO2 Electrodes
Authors: Avila Jason Ryan , Katz Michael Jacob , Farha Omar K. , Hupp Joseph T.
Published: February 2020

The understanding of electron transfer (ET) phenomenon across semi-conductor interfaces is crucial for applications in photovoltaic systems and electrochemical heterogeneous catalysis . In order to probe ET mechanisms, we exploit atomic layer deposition (ALD) to conformally coat ultrathin films of TiO2 onto a lower conduction band (CB) SnO2 electrode. Between TiO2 film thicknesses of 1 to 10 Å, quantum tunneling through the insulating TiO2 layer is the kinetically preferred ET pathway.  At films thicker than 10 Å, there is little change to the ET rate as a function of TiO2 thickness.  To our surprise, annealing a 55 Å layer of TiO2 on SnO2, a 10x reduction in ET rate was observed compared to the as deposited TiO2.  At potentials near the CB edge of SnO2, electrochemical impedance spectroscopy of nominally flat amorphous TiO2 indicated the presence of nearly double the density of states (DOS) with respect to their crystalline counterpart; the relationship between ET and DOS was studied in depth. These findings show the first observation of change in ET mechanism across semi-conductor interfaces, and demonstrates the ineffectiveness of thick layers films grown by ALD at completely shutting off electron transfer without annealing post film growth.
Cleaning Solution Effect on Electrical and Reliability Properties of Dense and Porous Low Dielectric Constant Materials
Authors: Cheng Yi-Lung , Huang Chi-Jia
Published: February 2020

The effects of different cleaning solutions and various immersion times on the electrical and reliability characteristics of the low-k dielectrics are investigated in this study. After immersing in a wet cleaning solution, both dense and porous low-k dielectrics are needed a post-baking process to remove the physically-adsorbed water. The experimental results indicate that the acid HF solution and basic NH4OH solution have negative impact on low-k dielectrics. Moreover, the acid HF solution causes the low-k dielectrics to be modified and a longer immersion time have larger impact. The formation of chemically-adsorbed water and the increased pore size or porosity in the low-k dielectrics with HF solution immersion were observed. These phenomena become more obviously in the porous low-k dielectrics with a longer immersion time. Except the positive benefit in the reduction of the dielectric constant, these changes cause the degradation in electrical and reliability performance for low-k dielectrics.
In Situ Precipitated Organic Nanorod Electrodes for Sodium Ion Batteries
Authors: Luo Chao , Wang Jingjing , Fan Xiulin , Zhu Yujie , Han Fudong , Suo Liumin , Wang Chunsheng
Published: February 2020

Organic electroactive materials derived from biomasses are promising candidates for next generation rechargeable batteries due to low cost, sustainability and environmental benignity. However, the organic electrodes still suffer from low power density and poor cycling stability, caused by low electronic conductivity and high solubility in liquid organic electrolytes. Herein, we firstly reported a unique in situ organic electrode fabrication technology for Na-ion batteries. Using the 2,5-Dihydroxy-1,4-benzoquinone disodium salt (DHBQDS) as an organic anode, the DHBQDS nanorod electrode is in situ formed during electrode fabrication process by precipitating DHBQDS from DHBQDS-sodium alginate-carbon black aqueous slurry film on a Cu current collector during drying process. In the slurry film, the sodium alginate binder and carbon black play a critical role in the formation of DHBQDS nanorods. Integrating the synthesis of nano-electrode materials into electrode fabrication process greatly simplifies the electrode preparation process and will significantly reduce the battery cost. Due to the fast ionic and electronic conduction of DHBQDS-carbon nanocomposite, the DHBQDS nanorod electrodes deliver a reversible capacity of 167 mAh g-1 at a high current density of 200 mA g-1 after 300 cycles, which is 87% of its initial capacity (capacity decay rate of 0.051% per cycle). To reduce the dissolution of DHBQDS in the electrolyte upon cycling, a thin layer of Al2O3 with thickness of 1nm or 2 nm was coated on the DHBQDS nanorod electrodes using atomic layer deposition (ALD). The Al2O3 coating remarkably suppresses the dissolution of DHBQDS nanorods as evidenced by the increased Coulombic efficiency from 94% to ~100% at a low current density of 50 mA g-1 after initial few activation cycles. The reversible capacity of Al2O3 coated DHBQDS nanorod electrodes remains at 212 mAh g-1 after 300 cycles with a very low capacity decay rate of 0.049% per cycle. The ALD enhanced organic nanorods exhibit the best reversible capacity and cycle life among the organic electrodes reported for Na-ion batteries.
Experimental and Theoretical Characterization of Electrode Materials That Undergo Large Volume Changes and Application to the Lithium-Silicon System
Authors: Verbrugge Mark W , Baker Daniel R. , Xiao Xingcheng , Zhang Qinglin , Cheng Yang-Tse
Published: February 2020

The life and performance of lithium-ion batteries is related to the mechanical expansion and contraction of the active materials, particularly for silicon-enhanced negative electrodes. In this work, we develop a theory and commensurate equations to describe how lithium diffuses within lithiated silicon, and we include the influence of active material expansion (upon lithiation) and contraction (upon delithiation). We employ thin-films of vapor-deposited Si to construct our electrodes. This allows us to isolate our analysis to the active material and avoids the necessity of treating binders, conductive diluents, and complicated geometries associated with conventional porous electrodes used in most practical lithium-ion batteries and in the construction and modeling of a Li-Si porous electrode. The model is shown to compare favorably with experimental results.

We have derived an equation system for the treatment of electrode materials that undergo large volume changes during operation. The approach is applied to a thin-film Li-Si system, wherein a volume change of about 270% is observed relative to pure Si and Li3.75Si. Good agreement is obtained when the model calculations are compared with experimental data obtained from Li-Si thin film electrodes (67-nm thickness) subjected to linear-sweep voltammetry experiments over current and potential ranges of interest for many applications, including electrified vehicles.

We ignore the influence of stress on the thermodynamics and transport of the Li-Si thin films. Instead, we use a one-dimensional model which assumes that stress does not impact the chemical potential, because the stresses are negligible within the infinitely thin film that is unconstrained at its interface with the electrolyte. However, the local expansion and contraction of the film, as a function of lithium content, is taken into consideration, and this leads to a moving boundary value problem, where the position of the film surface must be calculated.
Silicon/Carbon Nano-Composite Based Anodes for Advanced Lithium-Ion Batteries
Authors: Dobrowolny Sascha , Mahlendorf Falko , Heinzel Angelika
Published: February 2020

In the recent years, rechargeable lithium-ion batteries have gained in importance for electronic devices and electric vehicles. Thus, research and development focuses on improving energy and power densities as well as durability of lithium-ion batteries. Especially for high energy and power densities, the electrode materials must possess high specific storage capacities and coulometric efficiencies. However, state-of-the-art anode and cathode electrode materials, e.g. graphite and LiFePO4 exhibit high coulometric efficiencies but rather low theoretical storage capacities (372 and 170 mAh/g, respectively).

In the last decade silicon has become a promising anode material due to its high theoretical specific capacity of 3579 mAh/g at ambient temperature. However, this high specific storage capacity owing to host up to 3.75 lithium atoms per silicon atom leads to extreme volume expansion up to 280 % during lithiation, which results in pulverization and delamination of the electrode material after few cycles. Various approaches have been conducted to overcome these issues e.g. by using nano-sized active material or carbon coated silicon composite material.           

In addition to the materials science the electrode structure is of particular importance for the electrochemical performance. Electrode composition, binding mechanism due to the use of suitable binder polymers or particle size distribution of the active material are some exemplary parameters to stabilize the electrode structure and to handle such high mechanical stress during lithiation/delithiation.

Here we present electrochemical investigations of high capacity and high efficiency graphene coated silicon nanocomposite based electrodes prepared by using a wet chemical doctor blade manufacturing process. This active material provides a capacity of >2000 mAh/g with efficiencies >99% over more than 500 cycles. Investigations focus on influence of the stability of the electrode structure by using impedance spectroscopy, scanning electron microscopy, confocal microscopy and estimation of the coating adhesion strength. Cyclic voltammetry and galvanostatic cycling will show the applicability of improved Si/C composite based electrodes compared to conventional graphite based electrodes for lithium-ion batteries both in half cells as well as full cells in combination with commercially available cathode material.
In Situ Stress Measurements of Li-S Half-Cells during Electrochemical Cycling
Authors: Nation Leah , Tokranov Anton , Sheldon Brian W. , Woodford William H , Chiang Yet-Ming
Published: February 2020

Lithium polysulfide flow and semi-flow batteries are a candidate system for flow battery applications with the potential to achieve high energy and low cost. The insulating nature of lithium sulfide and the polysulfide shuttle process are challenges to feasibility. The formation of polysulfides and sulfides in Li-S half-cells are studied using thin-film graphitic carbon electrodes as a model surface. Raman spectroscopy is used to investigate the effect of carbon growth parameters and surface treatment on electrochemical performance. Stress evolution in a lithium polysulfide battery electrode is measured during electrochemical cycling using a Multi-beam Optical Stress Sensor (MOSS) through measurement of wafer curvature as an in situ technique to measure film growth. A significant reversible and irreversible stress response is observed during cycling. An irreversible stress is observed at lower potentials, which are associated with the formation of sulfides; a reversible stress response is seen during voltage holds at 2.6V during sulfur formation. Kinetic processes of the sulfur, polysulfide, and sulfide regimes are explored using potentiostatic holds. Multiple mechanisms can be distinguished in the voltage regimes explored as stress signatures and are shown to be influenced by prior voltage holds. Post-mortem samples are analyzed using electron microscopy and energy dispersive x-ray spectroscopy to provide insight into sulfide formation and stability.
(Invited) A Tale of Spinels: From Li-Ion to Mg Battery Electrodes
Authors: Cabana Jordi
Published: February 2020

Since the discovery by Thackeray and co-workers of their ability to reversibly intercalate Li, spinel oxides have become a canonical electrode material in battery technologies. Phases with this structure typically present very stable cycle life in the bulk and fast kinetics. When used as positive electrodes, the downside of spinel electrodes is their fairly low capacity and their interfacial instability. In Li-ion batteries, the best performance is obtained with significant amounts of Mn in the structure. Ions of these element, when redox active, are prone to corrosion processes that undermine the cyclability of the electrochemical cell. Further, while full intercalation from M2O4 (M=Mn, Ni, Co...) to Li2M2O4 is possible, it is also poorly reversible. As a result, practical applications limit the utilization to processes between M2O4 and LiM2O4. In other words, this material highlights the barrier of two electron reactivity that is pervasive in battery electrodes based on intercalation reactions.

In this talk, we will overview the strategies we have followed to expand the versatility of spinel oxides as reversible intercalation electrodes. We will discuss our efforts to understand the kinetic limitations of the Mn2O4-Li2Mn2O4 transition using high resolution chemical imaging. We will describe strategies to understand and impart interfacial stability, especially against corrosion processes that damage full battery performance. Finally, we will introduce evidence that this family of oxides could provide a path to explore positive electrodes for emerging multivalent technologies, with emphasis on Mg batteries.
Thermal Study of Reaction Intermediate Stability during Electrochemical Sulfur Reduction in a Lithium-Sulfur Cell
Authors: Seo Jeongwook , Sankarasubramanian Shrihari , Kim Chisu , Zaghib Karim , Prakash Jai
Published: February 2020

One of the most promising cell chemistries in the quest to surpass Lithium-ion cells in capacity is the Lithium-sulfur cell. The use of Sulfur, due to its high theoretical specific capacity (1675 mAh/g) and natural abundance, is the basis for this future potential. A step towards future development of this cell is the understanding of the complex reactions that occur at the sulfur cathode. The overall mechanism is the electrochemical reduction of octa-sulfur (S8) to Li2S with several intermediate lithium-sulfur composites. Prior research has involved the study of the plateaus and characteristics of the voltage profiles of these cells to try and elucidate the reaction mechanism.  Isothermal micro-calorimetry is a versatile tool to study reactions and understand their thermal behavior. Thermodynamic study of these reactions had been reported by the authors elsewhere. Herein we examine the stability of each intermediate by calculating the entropy change of their reaction step.  

The entropy change has negative value in the first and second electrochemical reaction stages which generate soluble lithium sulfur (Li2S8 and Li2S4). It changes to positive value when the electrochemical reaction produces insoluble lithium sulfur (Li2S2 and Li2S). The entropy change drops when DOD is 70%. This entropy change pattern exactly corresponds with the voltage profile with various potential plateaus which represents the electrochemical reaction stages. The entropy change values provide a fundamental understanding of the drivers of the electrochemical reaction, can be used to understand the stability of the various intermediates and also predict any new intermediates or reaction steps.
Elucidating the Requirements for Reversible Magnesium Electrodeposition and Dissolution
Authors: Barile Christopher J. , Barile Elizabeth C. , Spatney Russel , Zavadil Kevin R , Nuzzo Ralph G. , Gewirth Andrew A.
Published: February 2020

We compare the electrochemistry of Mg deposition and stripping from three Mg-battery electrolytes: EtMgBr, Mg(AlCl2EtBu)2, and MgCl2-AlCl3. These electrolytes represent three generations of progress in Mg-battery development, and include a simple Grignard reagent, an organohaloaluminate, and an all inorganic system, respectively. Our electrochemical measurements coupled with surface and bulk analytical techniques elucidate the requirements for reversible Mg deposition and definitively establish that voltammetric cycling of the electrolyte significantly alters their composition and performance.

In the cases of EtMgBr and Mg(AlCl2EtBu)2, electrochemical quartz crystal microbalance measurements demonstrate that mass is gained and lost from the electrode with relatively high efficiency. However, the charge passed during stripping is consistently less than that passed during deposition, resulting in chronoamperometric charge efficiencies between 80-100% for EtMgBr and 50-70% for Mg(AlCl2EtBu)2. SEM-EDS analysis of electrode surfaces demonstrates irreversible Mg deposition and stripping. GC-MS and NMR analysis of electrolytes reveal decomposition of the solvent-electrolyte system.

For the all inorganic system containing MgCl2-AlCl3 in THF, elemental analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy (SEM-EDS) results demonstrate that irreversible Mg and Al deposits form during early cycles. Electrospray ionization-mass spectrometry (ESI-MS) data show that inhibitory oligomers develop in THF-based solutions. These oligomers form via the well-established mechanism of a cationic ring-opening polymerization of THF during the initial synthesis of the MgCl2-AlCl3 electrolyte and under resting conditions. In contrast, solutions containing MgCl2-AlCl3 in 1,2-dimethoxyethane (DME), an acyclic solvent, do not evolve as dramatically at open circuit potential. From these results, we propose a mechanism describing how the conditioning process of MgCl2-AlCl3 in THF improves its performance by both tuning the Mg:Al stoichiometry and eliminating oligomers. We also explore the role that other solvents and metal chlorides play in the properties of inorganic Mg-battery electrolytes.
Direct Observation of Magnesium Ion Intercalation into a Spinel-Structured Î»-Manganese Oxide at the Multi Length Scale
Authors: Kim Chunjoong , Phillips Patrick J , Yi Tanghong , Key Baris , Key Baris , Yu Young-Sang , Klie Robert F , Cabana Jordi
Published: February 2020

The growing market of electric vehicles and grid storage requires the current battery technology to be further advanced. However, LIBs, the best energy storage system based on redox reactions, are intrinsically limited in their charge storage capacity by structural and/or electronic factors. Multivalent ion storage systems are attractive among the alternative systems because, while they closely resemble systems using Li-ion, they can store more charge per mol of intercalated species. In particular, Mg-ion batteries are of great interest to surpass the current performance barriers of Li-ion technology. There is only one proven working positive electrode material, Chevrel phase, for Mg ion battery at a relatively low working voltage window.1, 2 When searching for high voltage Mg-intercalation positive electrodes, most previous studies of the possible electrochemistry of oxide compounds Mg2+ electrolytes have provided little information on the reaction mechanisms leading to the electrochemical data.3  In this work, direct evidence of the reversible intercalation of Mg2+ into a spinel host was obtained. The structural changes observed after intercalation/deintercalation into the cubic spinel structure, λ-MnO2, and from tetragonal Mg
x
Mn3-x
O4 nanoparticles will be discussed.  Experimental observations by XRD, XAS, STEM-EDX, PDF and NMR were used to provide a robust understanding of the electrochemical reactions (see representative STEM-EDX in Figure 1).  The results confirm that spinel oxides are a potential cathode material for Mg batteries. They point at needs in the understanding of the mechanisms involved in multivalent ion storage, as well as the most efficient ways to characterize these reactions.

 ADDIN EN.REFLIST 1.            D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich, and E. Levi, Nature,
407 (6805), 724-727 (2000).

2.            H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour, and D. Aurbach, Energ Environ Sci,
6 (8), 2265-2279 (2013).

3.            C. Yuan, Y. Zhang, Y. Pan, X. Liu, G. Wang, and D. Cao, Electrochimica Acta,
116 (0), 404-412 (2014).

Figure 1
Electrolyte Additives for Reducing the Irreversible Capacity Loss, Impedance and Polarization of a Doped LiCoPO4 Cathode
Authors: Allen Joshua L. , Allen Jan L. , Delp Samuel A. , Jow T. Richard
Published: February 2020

High voltage cathode materials show promise for improving the energy density of the state-of-the-art lithium ion battery. One notable cathode material that displays a discharge voltage of ~4.8V, and has the potential to improve the specific energy to ~802Wh/kg, is the olivine-structured LiCoPO4. One significant issue, however, that has plagued LiCoPO4-based systems is the irreversible electrolyte decomposition that occurs at higher voltages. The electrolyte decomposition is further perpetuated by the requirement of a constant voltage charging step (trickle charge) that is necessary due to a lower electronic conductivity of the material and increasing interfacial impedance from the unstable electrolyte.

We have previously demonstrated that Fe-doped LiCoPO4 performs significantly better than neat LiCoPO4 by stabilizing the cathode structure and improving the electronic conductivity of the material (1). These structural changes, however, do not solve the problem of perpetual electrolyte decomposition that leads to polarization and loss of cycleable lithium.

In order to promote a low resistance passivation layer that prevents electrolyte decomposition, many researchers have incorporated electrolyte additives (2-3). We previously demonstrated that using electrolyte additives improves the performance of doped-LiCoPO4 half cells by forming a protective passivation layer on the cathode (4). The cathode half-cell performance can be somewhat misleading, however, because it does not take into consideration the loss of cycleable lithium due to irreversible redox reactions on the electrodes.

The present study serves as a next-step for demonstrating the viability of our doped-LiCoPO4 cathode for the production of high specific energy Li-ion batteries. Full coin cells were fabricated and tested, including a next-generation LiCoPO4-doped cathode (developed by ARL) and a standard graphite anode. Various electrolyte additives were examined with the new cathode to minimize the first cycle irreversible capacity loss, reduce the interfacial impedance, and promote a long cycle life. These additives include tris(hexafluoro-iso­-propyl)phosphate (HFiP), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), fluoroethylene carbonate (FEC), trimethylboroxine (TMB), and other ARL-proprietary additives. These additives significantly improved the performance when compared to the baseline electrolyte.

ACKNOWLEDGEMENT

The authors wish to express their gratitude to the DOE ABR program for partial financial support.

REFERENCES

J.L. Allen, T.R. Jow and J. Wolfenstine, J. Power Sources,
196, 8656 (2011).

R. Sharabi, E. Markevich, K. Fridman, G. Gershinsky, G. Salitra, D. Aurbach, G. Semrau, M.A. Schmidt, N. Schall and C. Bruenig, Electrochem. Commun., 28, 20 (2013).

M. Hu, J. Wei, L. Xing and Z. Zhou, J. Appl. Electrochem., 42, 291 (2012).

J.L Allen, J.L. Allen, S.A. Delp, T.R. Jow, ECS Trans.
27, 63-68 (2014)
Invesitgation of the Gas Generation in Lithium Titanate Anode Based Lithium Ion Batteries
Authors: Fell Christopher Ryan , Sun Liyuan , Hallac Peter B , Metz Bernhard , Sisk Brian C
Published: February 2020

Lithium ion batteries containing lithium titanate (LTO), Li4Ti5O12 are promising energy storage systems for their high rate capabilities, safety, and long cycle-life. However, gas generation and associated swelling, which can be observed under high-temperature operation, present a challenge to the large-scale application of lithium ion batteries made from LTO anodes. Research has suggested various causes for gas generation,  including residual moisture in the electrodes and electrolyte [1] and catalysis involving the Ti3+/Ti4+ redox couple combined with water electrolysis.[2,3]  It is important to understand the source of gas generation so as to avoid it with proper manufacturing conditions, such as tight control over moisture levels.  However, at this time the mechanism of gas evolution from LTO anode based lithium ion battery systems is not well established.

Here we analyzed LTO cells following high temperature (80ºC) calendar life storage at 100% SOC. We explored the relationship between volume expansion and impedance increase following high temperature storage. The results in Figure 1 indicate that with increasing gas volume expansion, the performance of the cells degrades. The gas species and quantities resulting from the cell volume expansion were collected and analyzed post-mortem using quadrupole mass spectrometry (MS) and combined gas chromatography / mass spectrometry (GC/MS). With this method, we introduced varying levels of water content into the cathode and anode, as well as the electrolyte. To facilitate determination of the origin of gas generation, we utilized deuterated water (D2O) introduced into the electrodes and electrolyte as well as 5% deuterated dimethyl carbonate (DMC) and ethylene carbonate (EC) based electrolytes. Figure 2 illustrates a comparison of gas compositions obtained from cells with 1600ppm D2O added to the electrolyte and 5wt% deuterated DMC in the electrolyte. The preliminary results illustrate that deuterated DMC in the electrolyte shows negligible breakdown to yield D2 based gas when compared to samples that contain heavy water (D2O) added into the electrolyte. This indicates that the primary source of gas generation in LTO based cells originates from residual moisture in the electrodes and electrolyte.  This result reinforces the importance of maintaining low-moisture processing conditions for LTO-based lithium ion batteries.

(1) Belharouak, I.; Koenig, G. M.; Tan, T.; Yumoto, H.; Ota, N.; Amine, K. Journal of the Electrochemical Society
2012, 159, A1165.

(2) He, Y.-B.; Li, B.; Liu, M.; Zhang, C.; Lv, W.; Yang, C.; Li, J.; Du, H.; Zhang, B.; Yang, Q.-H.; Kim, J.-K.; Kang, F. Sci. Rep.
2012, 2.

(3) Bernhard, R.; Meini, S.; Gasteiger, H. A. Journal of the Electrochemical Society
2014, 161, A497.

Figure 1
Preferentially Orientated Li-Deficient Li4Ti5O12 Nanosheet Anode and Its Excess Charge Storage Properties
Authors: Chiu Hsien-Chieh , Zhou Jigang , Gu Lin , Reid Joel , Lu Xia , Gauvin Raynald , Zaghib Karim , Demopoulos George P.
Published: February 2020

Mesoporous Li deficient Li4Ti5O12 nanosheets with major [110] preferred orientation were prepared by a novel low T (<100 °C) aqueous synthesis process. Surface relaxation due to nanosize effect in the near surface region and 10 % deficiency of lithium were found to lead to local chemical bond length extension that influences the electronic structure and Li storage capacity. Thus the lithiated material over the potential range from 1 to 2.5 V vs. Li/Li+ reaches the following over-stoichiometrical composition: Li7.92Ti5O12. As determined by XANES the excess Li-ion storage is the result of preferential crystal orientation along the (110) and (111), facets. During lithiation, it was further determined the charge compensation to occur primarily by oxygen, rather than by titanium. Finally, both the oxygen and titanium in the near surface region exhibit different electronic structure from bulk. Those results point to the importance of surface reconstruction and relaxation in accommodating excess Li storage. As a consequence, the newly prepared Li4Ti5O12 nanosheets exhibit superior Li-ion storage performance exceeding by far most of the alternatively prepared LTO anode materials.
Tuning Particle Morphology of Lithium-Ion Battery Electrode Particles
Authors: Koenig Gary , Robinson Pierce
Published: February 2020

Improving energy density and performance of lithium-ion battery electrodes is highly dependent on improvements in electrode and electrolyte chemistry, however, the morphology of the active materials also can play a major role.  Particle morphology has a major impact on factors such as the packing of particles into electrodes and the relative amount of surface area exposed to the electrolyte per mass of material.  In this presentation, we will describe our current efforts to synthesize lithium-ion battery electrode particles that are relatively monodisperse and have tunable overall shape and surface morphology.  Our group is taking advantage of inorganic solution chemistry methods and understanding particle nucleation and growth to control the final resulting particle morphology that will eventually serve as lithium-ion battery active materials.  This work will focus on our first efforts investigating a model system for building a library of particle morphologies for a single battery chemistry, in this case LiMn2O4.
In-Situ TEM Observation of Random Solid Solution Zone in LiFePO4 Electrode
Authors: Niu Junjie
Published: February 2020

Olivine structured LiFePO4 (LFP) as electrode material has attracted great interest in the Li-ion battery community. Recently there are debates on the presence and roles of solid solution zone (SSZ) in lithiation/delithiation, originating from the apparent high rate capability of LFP battery despite poor electronic/ionic conductivities of bulk LiFePO4 and FePO4. A potentiostatic in-situ transmission electron microscopy (TEM) technique was used to study the LiFePO4 electrode kinetics during delithiation. On the basis of real time high-resolution TEM analysis, SSZ forms quickly and reaches 10-25 nm × 20-40 nm on ac face that directly contacts the electrolyte, in lieu of sharp LiFePO4→FePO4 interfaces observed in some other situations. This 20 nm scale SSZ was apparently quite stable and persisted for hundreds of seconds duration of our experiment. In contrast to atomically sharp LiFePO4→FePO4 interface, the wide SSZ seen here contains no dislocations, so reduced fatigue and enhanced cycle life can be expected along with enhanced rate capability. These findings suggest that SSZ can dominate electrode transformation when the particle size reaches sub-100 nm; for larger particles, SSZ could still be important during fast charging, as it provides out-of-equilibrium but atomically wide avenues for Li+/e- transport (Nano Letters, 14 2014 4005).
First Principles Study of Hybrid Li-Ion/Li-O2 Battery Materials
Authors: Kinaci Alper , Trahey Lynn , Wolverton Chris , Thackeray Michael M. , Chan Maria K. Y.
Published: February 2020

Using first principles density functional theory (DFT) calculations, we explore a class of materials which facilitate both Li-ion and Li-O2 reactions. These "hybrid" materials contain high lithium and oxygen contents together with a transition-metal oxide component. The prototype hybrid Li-ion/Li-O2 material is Li5FeO4 which, when used as an electrocatalyst in Li-O2 cells, reduces overpotentials and demonstrates a high capacity of ~500 mAh/g unrelated to Li2O2 formation. While hybrid materials exhibit promising capacities of up to 1000 mAh/g, their reaction mechanisms remain unknown. We performed DFT investigations of the reaction mechanisms in several of these materials, including Li5FeO4, Li6MnO4, Li6CoO4, and Li8IrO6. DFT calculations are performed to investigate the thermodynamics of Li and Li-O removal from these materials, in order to establish the details of the charge reaction. Atomistic and electronic structural changes in the materials are tracked during the reactions. Results on the energetics indicate a cross-over between pure lithium removal and concomitant oxygen loss, which is electronically shown to be correlated with development of the peroxide-like character of oxygen.
Prussian Blue As Negative and Positive Electrode in Lithium and Sodium-Ion Batteries
Authors: Piernas-Muñoz María José , Castillo-Martínez Elizabeth , Armand Michel , Rojo Teófilo
Published: February 2020

Prussian Blue, ideally KFeIIIFeII(CN)6·xH2O, and its analogues, KMIIFeIII(CN)6·xH2O (M=Mn, Fe, Co, Ni, Cu, Zn), have been successfully proved to work as cathodes in lithium ion-batteries (LIB) or sodium ion-batteries (NIB), both in organic or aqueous media.[1],[2],[3],[4] The combination of the transition metals redox properties presents in the PB structure along with the large available channels for ion diffusion[5] make  it  a good candidate both for positive and negative electrode either in LIB or NIB.

We recently reported the performance of Prussian Blue (from now on abbreviated as PB) acting as anode versus lithium in organic media. In the low voltage window of 1.6 - 0.005 V, it exhibits a plateau at ca. 0.9 V and capacities comparable to those observed for graphite (450 mAh/g in the first cycle and 350 mAh/g after 50 cycles at 8.75 mA/g), which are 5 times higher than the theoretically expected for the insertion of 1 Li+ per formula unit through an intercalation mechanism. Based on several evidences observed when ex-situ experiments are carried out in the discharged electrodes, we proposed a conversion (or displacement) mechanism, for the first time reported, as the reaction probably taking place.[6]

On the other hand, the already contrasted performance of the potassium PB as cathode, in combination with the increasing interest in new alternatives to lithium, providing less expensive and more environmentally friendly materials, such as the NIB, led us to consider the sodiated phase of PB, ideally NaFeIIIFeII(CN)6·xH2O, to work as cathode material versus sodium in organic media. The presence of sodium ions in the crystal structure of the pristine material could facilitate the insertion/deinsertion of these alkali ions.[7] Herein, we will present the study on the optimization of the electrochemical behaviour of the sodium system, which shows 2 plateaus at 2.7 and 3.45 V and capacities up to 140 mAh/g, in NIB. The mechanism of insertion/deinsertion will be also discussed.

[1] J. Electrochem. Soc., 2012, 159, A98. Colin D. Wessells, S.V. Peddada, M.T. McDowell, R.A. Huggins and Y. Cui.

[2] Inorg. Chem., 2002, 41, 5706. A. Widmann, H. Kahlert, I. Petrovic-Prelevic, H. Wulff, J.V. Yakhmi, N. Bagkar and F. Scholz.

[3] Chem. Commun.,
2012, 48, 6544. Y. Lu, L. Wang, J. Cheng and John B. Goodenough.

[4] Chem. Commun. 2013,49, 2750. T. Matsuda, M. Takachi and Y. Moritomo.

[5] J. Phys. Chem.
1981
, 85, 1225. D. Ellis, M. Eckhoff and V.D. Neff.

[6] J. Power Sources, 2014
, 271, 489. M.J. Piernas-Muñoz, E. Castillo-Martínez, V. Roddatis, M. Armand and T. Rojo.

[7] Energy Environ. Sci.,
2014
, 7, 1643. Ya You, Xing-Long Wu, Ya-Xia Yin and Yu-Guo Guo.
Simulations with an Accurately Calibrated Electrochemical Model of Li-Ion Battery to Determine Additional Aging Mechanisms
Authors: Edouard Clément , Forgez Christophe , Revel Renaud , Bernard Julien , Petit Martin
Published: February 2020

The growing number of electrified vehicles remains particularly constrained by the performance of the energy storage system, which is a complex and expensive component in the vehicle. Li-ion batteries seem to be the best candidates due to their suitable performances for plug in or full electric vehicle application. However, the aging phenomena in those batteries will have a direct impact on the autonomy, power and maintenance costs of the vehicle and are not yet clearly understood. For automotive industry, this kind of information is critical in determining the performance and durability of the battery in traction applications. For that reason, there is an urgent need of validated predictive models for the long term behavior of those electrochemical components, ensuring an optimal battery sizing on one hand, and a proper energy management onboard on the other hand.

The aging of a Li-ion battery is mainly due to a modification of its electrochemical properties which will lead to a loss of capacity (decrease of the autonomy) and an increase of its internal impedance (loss of power). A simplified electrochemical model has already been developed at IFP Energies Nouvelles[1] taking into account the loss of cyclable lithium due to the growth of the Solid electrolyte Interphase (SEI) and the modification of the porosity of the graphite electrode as aging mechanisms. This model allows us to estimate the evolution of the performance (power and autonomy) of a Graphite/LiFePO4-based battery as if it was used on a typical hybrid or electric vehicle. In order to ensure the reliability of this model, a sensitivity analysis based on Zhang et al. work[2] has been performed to find out the impact of the variation of each parameters on the model output (Voltage, Temperature) and determine the optimal testing conditions for this model calibration.

Moreover, the discrepancies observed during the validation of our properly calibrated model with experimental data highlighted an additional capacity loss due to another aging mechanism than SEI growth. According to our previous research and to the literature, we decided to add a mechanical stress based mechanism involving cracking into the electrode that leads to a loss of active materials or enhances the loss of lithium inventory. Therefore, specific experiments inducing stress during intercalation of lithium ions in the negative electrode have been carried out to gather data to identify parameters of the new mechanism added to our model. Afterwards, the behavior of this new aging model will be validated on dynamic PHEV duty profiles to ensure its good reliability.

References

[1]          E.Prada, Di Domenico D., Creff Y., Bernard J., Sauvant-Moynot V. et al., J.Electrochem.Soc. 160 (2013) A616-A628.

[2]          L.Zhang, Lyu C., Hinds G., Wang L., Luo W. et al., J.Electrochem.Soc. 161 (2014) A762-A776.
Electrophoretic LiFePO4/ Graphene Composite for Li-Ion Battery Cathode Application
Authors: Li Quan
Published: February 2020

LiFePO4 (LFP) is a most promising cathode material for lithium ion batteries (LIBs) due to its high theoretical capacity (170 mAh g-1), flat voltage plateau, long cycle life, abundant material supply, and excellent safety.  However, it suffers from low electronic conductivity, which results in sacrificed capacity and low rate performance of the cathode.  Finding efficient additives that enhances the electronic conductivity of LFP, while at the same time minimizing the content of both additives and binders, become a tempting goal as it would lead to high performance cathode with high packing density.  

In the present work, we demonstrate a binder free composite electrode of LiFePO4/ graphene with ultrahigh LiFePO4 mass ratio (91.5 wt% of LiFePO4) using electrophoresis. No additional additive (other than graphene) is introduced.  Enhanced capacity and improved rate performance have been demonstrated in the electrophoretic composite cathode, when compared to either the conventional one or composite cathode formed by mechanically mixing LiFePO4 and graphene. A number of key material/processing parameters have been investigated in a systematic manner in order to understand their effect on the final cathode electrochemical performance as well as identify the optimum composite cathode configuration. We also extend our discussion onto the beneficial effect of using three dimensional current collectors and the role of different ions employed during the electrophoresis process. The present methodology is simple and does not disturb the active material growth process. It can be generally applied to a variety of active material systems for both cathode and anode applications in Li-ion batteries. This work is supported by General Research Funding of the National Natural Science Foundation of China/ Research Grants Council Joint Research Scheme under project No. N_CUHK448/13.