bluuebunny/crossref_metadata_2025 huggingface dataset:
Confined Lithium-Sulfur Reactions in Narrow-Diameter Carbon Nanotubes
Authors: Guo Juchen
Published: February 2020

We demonstrate an unusual electrochemical reaction of sulfur with lithium upon encapsulation in narrow-diameter (sub-nanometer) single-walled carbon nanotubes (SWNTs). Our study provides mechanistic insight on the synergistic effects of sulfur confinement and Li+ ion solvation properties that culminate in a new mechanism of these sub-nanoscale-enabled reactions (which cannot be solely attributed to the lithiation-delithiation of conventional sulfur). Two types of SWNTs with distinct diameters, produced by electric arc (EA-SWNTs, average diameter 1.55 nm) or high-pressure carbon monoxide (HiPco-SWNTs, average diameter 1.0 nm), are investigated with two comparable electrolyte systems based on tetraethylene glycol dimethyl ether (TEGDME) and 1,4,7,10,13-pentaoxacyclopentadecane (15-crown-5). Electrochemical analyses indicate that a conventional solution-phase Li-S reaction occurs in EA-SWNTs, which can be attributed to the smaller solvated [Li(TEGDME)]+and [Li(15-crown-5)]+ ions within the EA-SWNT diameter. In stark contrast, the Li-S confined in narrower diameter HiPco-SWNTs exhibits unusual electrochemical behavior which can be attributed to a solid-state reaction enabled by the smaller HiPco-SWNT diameter compared to the size of solvated Li+ ions. Our results of the electrochemical analyses are corroborated and supported with various spectroscopic analyses including operandoRaman, X-ray photoelectron spectroscopy, and first-principles calculations from density functional theory. Taken together, our findings demonstrate that controlled solid-state lithiation-delithiation of sulfur and an enhanced electrochemical reactivity can be achieved by sub-nano encapsulation and one-dimensional confinement in narrow-diameter SWNTs.
Corrosion Monitoring and Control in Molten Chloride Based Concentrated Solar Power Systems
Authors: Guo Jicheng , Hoyt Nathaniel C. , Williamson Mark A.
Published: February 2020

Molten mixtures of MgCl2-KCl-NaCl are promising heat transfer fluid (HTF) candidates for the next generation concentrated solar power systems (Gen3 CSP), because of their low cost, high decomposition temperature, and favorable heat transfer characteristics. However, if not properly controlled, molten chloride salts can cause the corrosion of high-temperature metal alloys, such as Inconel, in CSP systems. Here we demonstrate an automated corrosion monitoring and control system that can be used to maintain the health of the structural alloys over long durations. The monitoring system includes a multifunctional voltammetry sensor that is able to measure the redox potential of molten MgCl2-KCl-NaCl mixtures as well as the presence of corrosion products. The sensor is capable of detecting corrosion products, such as Cr2+ and Fe2+, quantitatively at low concentrations (less than 100 ppm) with less than 2% error. The corrosion control capability is facilitated by the in-situ electrolytic production of Mg metal that is automatically initiated when the sensor indicates salt conditions favorable to corrosion. The results show that the corrosion is effectively mitigated when the salt potential is maintained to be sufficiently cathodic.

The submitted abstract has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan. http://energy.gov/downloads/doe-public-access-plan
Understanding the Scales Formation Inhibition Mechanism on C-Steel in a Sour Media
Authors: Al-Qahtani Noora , Qi Jiahui , Abdullah Aboubakr Moustafa , Laycock Nick , Ryan Mary P.
Published: February 2020

Corrosion control in sour environments is a severe challenge for the oil and gas industries with respect to sour media. One of the approaches to mitigate such a problem is to use corrosion inhibitors (CI). The selection of a single (or a mixture of) CIs for a particular oil or gas production, transportation system or storage facility depends on its condition. In sour oil or gas media, depending on the ratio between carbon dioxide and hydrogen sulfide in the gas, pH, pressure, temperature, and brine chemistry, various kinds of iron sulfide and iron carbonate product layers can be formed. To control such formation scales of iron sulfides, it is essential to understand the mechanisms of corrosion inhibition in H2S systems. In this work, the electrochemical behaviour of C-steel in sour (i) de-ionised water (DIW) and (ii) in different NaCl solutions were examined in an H2S system. A series of experiments were conducted at ambient (RT), 50 oC and at 80 oC using different combinations of inhibitors (A and B). The corrosive behaviour of C-steel was investigated by measuring the open circuit potential (OCP), linear polarisation resistance (LPR), and potentiodynamic polarisation (PDP) in addition to scanning electron microscopy (SEM) coupled with an energy dispersive X-ray (EDX) and Raman spectroscopy (RS). The outcome has shown that the corrosion rate of C-steel initially decreased and then stabilised with time in the CI solution that might be linked to the inhibition effect of the corrosion product layers on the iron surface. SEM analysis shows that no film of corrosion products existed. CIs control the corrosion process and prevent passive film formation (iron sulfide), even with the presence of H2S in all tests.
(Invited) Operando Investigation of All-Solid-State-Batteries Using Li3PS4 Solid Electrolyte
Authors: Hoeltschi Laura , Wu Xiaohan , Billaud Juliette Marie , Villevieille Claire
Published: February 2020

All-solid-state batteries have been presented as the ideal solution to address i) the safety limitations of conventional Li-ion batteries by suppressing the flammable organic electrolytes and ii) the problem of insufficient energy densities. To date, two types of solid Li-ion electrolytes have been mainly studied, namely, sulfur-based and ceramic-based materials. Despite the progress in the development of superionic conductor, many aspects of their reaction mechanisms and stability upon cycling still remain non-elucidated.

In order to get a better insight about their stability upon cycling, the development of a reliable electrochemical cells is thus of a prime importance when studying battery materials in operando mode during cycling. This is never an easy task, since the design of such cells has to be adequate to the technique of a choice and meet all necessary requirements. However, once a proper design is found, the surface, the bulk, the interfaces, and finally the combination of those can be studied and lead to the elucidation of the reaction mechanisms, thus further improving the battery technology.

Unfortunately, in most cases the electrochemical cells used for operando measurement are not ideal and suffer from low internal pressure (i.e. poor contact between the electrodes). It shorts the lifespan of the cell, especially in the case of all-solid-state-batteries. Herein we present different cell designs developed in our laboratory and used for operando studies.

Through this presentation, we will use bulk, surface and imaging techniques to better understand the limitation of all solid state batteries. As an example, Operando neutron imaging has been employed to understand the Li diffusion within the electrode and inside an all-solid state batteries employing Li3PS4 as solid electrolyte whereas operando X-ray microscopic tomography was employed to follow the possible electro-mechanical fracture occurring during cycling and the possible impact on the electrochemical performance.
(Invited) In-Situ X-Ray Imaging Analysis of Diffusion Phenomena in All-Solid-State Battery Using Ag-Ion
Authors: Orikasa Yuki , Kandori Koji , Yamashige Hisao , Furuta Noritoshi , Nonaka Takamasa
Published: February 2020

All-solid-state rechargeable battery is one of the candidates of post-lithium-ion batteries. In recent years, the intrinsic charge-discharge performance of active materials and the ionic conductivity of solid electrolytes have dramatically improved; however, the dynamic behavior of carrier ion in the composite electrode has not been understood for the performance of battery pack. If the transport number in the solid electrolyte is almost one, it is considered that salt concentration distribution does not occur in principle. Due to this advantage, the thicker electrodes can be realized for all-solid-state rechargeable battery. However, as far as the authors know, the direct observation of carrier ions during operation of all-solid state rechargeable batteries has not been reported. This is because it is difficult to observe the behavior of lithium ions which are general carrier ions but are light elements. Therefore, in this research, as a model of all-solid-state rechargeable batteries, we used silver ion conductor which shows much high ionic conductivity. The dynamic behavior of silver ion in solid electrolyte and electrode during battery operation was investigated by high energy X-ray imaging method with synchrotron radiation.

Ag6I4WO4 was used as the solid electrolyte, and in the case of the electrolyte observation, silver used as both electrodes. The pressed cell component was sliced with the thickness of 300 mm. In the case of the electrode observation, TiTe2 was used as the working electrode and silver was used as the counter electrode. X-ray transmission imaging measurements were performed in SPring-8.

Compared with the reference samples of Ag6+xI4WO4 (x = 0, 0.06, 0.17, 0.31), it was shown that noticeable ion concentration distribution similar to that of the battery using the organic electrolytic solution as the electrolyte during charge / discharge does not occur. On the other hand, dendrite growth in the solid electrolyte due to silver deposition and reaction distribution in the electrode were observed. In this presentation, we will provide the direct observation of silver ion diffusion in composite electrode.
(Keynote) A Path Forward to Low-Cobalt or Cobalt-Free Cathodes for Lithium-Ion Batteries
Authors: Manthiram Arumugam
Published: February 2020

Lithium-ion batteries have become the choice of power source for portable electronics as they offer much higher energy density than other rechargeable systems. They are also in the process of transforming the transportation sector and beginning to penetrate the utility industry for grid storage of electricity produced from renewable sources like solar and wind. The lithium-ion battery industry is now based on layered LiMO2 cathodes with fractions of M = Mn, Co, and Ni as each of them has its own advantages and disadvantages. For example, Mn offers good chemical stability without oxygen release, while Co suffers from oxygen release on charging LiCoO2 beyond ~ 50% as the Co3+4+: t2g band overlaps with the top of the O2-:2p band. In contrast, Co offers good structural stability without migrating from the transition-metal layer to the lithium layer via the neighboring tetrahedral sites due to the high octahedral-site stabilization energy, while Mn migrates readily to the lithium layer resulting in a layered to spinel-like phase transition due to the low octahedral-site stabilization energy. Also, Mn is abundant, environmentally benign, and less conductive, while Co has limited abundance, is relatively toxic, and becomes metallic on charging. Ni is in between Co and Mn in all these criteria. To make use of the best out of each of these three ions, the industry is now based on LiNi1-y-zMnyCozO2 with (1-y-z) < 0.6 and a significant fraction of Co (z > 0.2). There is a significant drive to reduce the fraction of Co or eliminate it altogether and increase the fraction of Ni. However, LiMO2 cathodes with a high fraction of Ni suffer from a few serious issues: capacity fade, thermal instability, and air-reactivity due to (i) a series of phase transitions causing internal stress, (ii) high surface reactivity with the electrolyte resulting in the formation of thick solid-electrolyte interphase, and (iii) high surface reactivity with ambient air resulting in a significant amount of LiOH and LiHCO3 on the surface.

This presentation will first focus on a fundamental understanding of the bulk and surface instability of layered LiMO2 cathodes, employing advanced characterization tools, such as time-of-flight secondary ion mass spectrometry, x-ray photoelectron spectroscopy, and aberration-corrected transmission electron microscopy, to probe both the layered oxide cathode and graphite anode subjected in full lithium-ion cells to extended cycling (up to 1,500 cycles). The presentation will then focus on developing LiMO2 cathodes with a cobalt content of as low as 6% with appropriate cationic doping and surface stabilization. Finally, it will also present a path forward to develop cobalt-free LiMO2 cathodes. Based on the strategies, cathodes with capacities of as high as 220 mAh/g with good cycle life and air stability will be presented.
(Invited) Identification of Cathode Materials for Ca Batteries
Authors: Torres Arturo , Luque Javier , Tortajada José , Arroyo-de Dompablo M. Elena
Published: February 2020

In the last years, concerns on Li availability have aroused the search for suitable alternatives to rechargeable Li-ion batteries. An attractive alternative is to combine sustainability with prospects of high energy density and develop metal anode technologies based on multivalent abundant elements such as Ca. The development of the Ca-ion technology requires technical advances to overcome the existing hurdles concerning electrolytes, electrodes and cell design1-3. Identifying cathode materials enabling effective diffusion of Ca2+ ions is far from being evident and, to the date, none of the investigated materials develops a stable high specific capacity with cycling 1-3.

In order to identify potential cathode materials for the Ca batteries, we have carried out a Density Functional Theory investigation to quickly screen a variety of structures and compositions. The screening started with a pre-selection of candidate compounds from the Inorganic Crystal Structure Database (ICSD). For the selected compounds, the general strategy is firstly to calculate average voltage and volume changes associated to the redox reaction. In a second step, DFT calculations for the promising materials are performed to gain information of electronic and ionic conductivities, crystal structure of reduced/oxidized phases and possible phase transformations. Fifty Ca-transition metal compounds including oxides, sulphides, nitrides, carbonates and phosphates were preselected from the ICSD. Out of this set, 25 ternary oxides and the minerals belonging to the pyroxene, garnet and double carbonates groups have been analysed in deep. The results will be discussed in this communication.

Acknowledgments: Authors are grateful for financial support from European Union H2020-FETOPEN funded project CARBAT-766617.

References:

A. Ponrouch and M. R. Palacin, Current Opinion in Electrochemistry, 2018, 9, 1-7.

R. J. Gummow, G. Vamvounis, M. B. Kannan and Y. He, Advanced Materials, 2018, 30, e1801702.

P. Canepa, G. S. Gautam, D. C. Hannah, R. Malik, M. Liu, K. G. Gallagher, K. A. Persson and G. Ceder, Chemical Reviews, 2017, 117, 4287-4341.
(Invited) Understanding Interfacial Reaction of LiCoO2 Positive Electrode in Aqueous Lithium-Ion Batteries
Authors: Byon Hye Ryung , Oh Hyunjung , Yamagishi Hirona , Yamanaka Keisuke , Ohta Toshiaki
Published: February 2020

Since the risk of catch fire using non-aqueous electrolyte solution, aqueous solution-based rechargeable lithium batteries (ARLB) have been highlighted. However, the conventional positive electrodes of lithium transition-metal oxide such as LiCoO2 (LCO) and LiNi1/3Mn1/3Co1/3O2 (NMC) have suffered from poor cyclability in aqueous medium. Representatively, the layered two-dimensional structure of LCO shows notably poor stability, possibly due to the surface degradation from water [1] and proton [2]. The understanding of interfacial reaction of LCO in the aqueous electrolyte solution is still superficial however.

Here we present degradation phenomena of LCO electrode in aqueous medium using various X-ray measurement techniques, and suggest the solution to avoid such an irreversible electrochemical reaction. The aqueous solution was prepared with 0.5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and pH was controlled to ~6.8 and 10. In both cases, there was no evidence for the formation of cathode-electrolyte interphase (CEI) on LCO in contrast to the one with non-aqueous electrolyte solution. The direct contact of aqueous electrolyte solution to LCO surface results in the short-range disorder of LCO structure such as the distortion of octahedral CoO6, and irreversible Li+ desertion during 10 cycles. To improve electrochemical reversibility and structural stability of LCO, we prepared the organic protection layer that opened the Li+ mass transport route while inhibiting H2O contact from hydrophobic surface. As a result, the capacity retention was improved to ~85% during 30 cycles at pH ~ 6.8. Furthermore, we developed the way to protect LCO surface by anion engineering and in the absence of protection layer, which give insight into the inner Helmholtz plane (IHP) structure and its effect for LCO degradation in aqueous medium.
(Plenary) Materials for High Energy Density Li and Li-Ion Batteries
Authors: Whittingham M. Stanley
Published: February 2020

Over the last decade the energy density of lithium-based batteries has gradually increased, but commercially available cells have now topped out at around 200-250 Wh/kg at the cell level. I will describe several materials-centered approaches that will allow in excess of 300-350 Wh/kg and 700 Wh/l. First the carbon-based anode must be replaced by a higher capacity material, preferably lithium metal itself; we have found that tin-based anodes can achieve 50-100% greater capacity than carbons with coulombic efficiencies over 99.5%. Second on the cathode side, I will describe two options: two-electron systems using lithium, and high nickel NMCAs, both of which have theoretical energy densities of around 1 kWh/kg and have the capability of attaining 1 kWh/liter. The safety aspects will also be covered, as will alternatives to lithium. This work is supported by SUNY, NYS-ESD, NYSERDA and US DOE, BES-EFRC and EERE-VTO-BMR.
(Invited) Distinguishing Productive and Parasitic Processes in Electrochemical Energy Storage Systems — Complementary Insights from Ex Situ, In Situ and Operando Spectroscopy, Diffraction and Electrochemistry Studies
Authors: Marschilok Amy C.
Published: February 2020

Conceptually, there are two related electrochemical storage mechanisms for electrochemical energy storage materials: insertion where an ion inserts into a structure on reduction and then is removed from the structural lattice upon oxidation, and conversion where there is a chemical reaction leading to a new material or phase. For some materials, each of these mechanisms may participate at different stages of the electrochemical redox process, where the kinetics for ion and electron transport can play a determinstic role regarding which process dominates at a particular state of (dis)charge. Parasitic side reactions can also make significant contributions to the function of the energy storage system, including through formation of resistive interfaces and consumption of redox active material/s. Complementary insights in distinguishing productive and parasitic processes gained from ex situ, in situ, and operando spectroscopy, diffraction and electrochemistry studies will be highlighted in this presentation.
Direct Liquid Fuel Cells By Using Hypophosphites
Authors: Wang Ren-He , Wu Meng-Jia , Haller Servane , Metivier Pascal , Wang Yong-Gang , Xia Yong-Yao
Published: February 2020

Direct liquid fuel cells (DLFCs) are promising power sources for future portable, wearable or implantable electronic devices owing to their high energy density and low emissions. Large efforts have been given for the development of DLFCs since 1990s, however the wide spread commercialization of DLFCs is still limited by the high cost coming from the expensive noble metal catalysts and proton exchange membranes. Furthermore, the safety risks related to organic fuels (methanol, ethanol and formic acid), such as toxicity and flammability, bring up tremendous consideration in fuel cell design, fuel distribution and transportation [1]. Finally, the emission of CO2 is inevitable by using organic fuels, which escalates to Green House Effect.

In this work, we proposed a new category of inorganic fuels for DLFCs. Hypophosphite is a type of food additive, therefore no safety hazards at all, and is also a strong reductant whose electrochemical oxidation reactivity is strongly correlated to metallic palladium [2]. Moreover, the inorganic fuels could realize “Zero Emission” after “Burning”. From thermodynamic calculations, the theoretical cell voltage and volumetric energy density at 1M are 2.05 V and 188 Wh/L at standard conditions, which are comparable and even better than the data of DMFCs (Direct Methanol Fuel Cells).

The unique electrochemical oxidation behavior of hypophosphites on Pd catalyst brings advantages in simplifying fuel cell structure and broadening our selections of cathodic catalysts for ORR (Oxygen Reduction Reaction). Herein, we report the investigation of catalyst design and cell design of a novel membrane-free Direct Hypophosphite Fuel Cell (DHPFC), which showed an open circuit voltage of 1.0 V and a maximum power density of 32 mW cm-2 under air flow at 25 oC. The oxidation mechanism of hypophosphites on Pd was also studied in this work.

This work is financially sponsored by Solvay and “Shanghai Rising-Star Program” (16QB1404600).

Reference:

[1] G. L. Soloveichik, Beilstein J. Nanotechnol.
2014, 5, 1399-1418.

[2] N. Fujiwara, Z. Siroma, T. Ioroi, K. Yasuda, J. Power Sources
2007, 164, 457-463.
Surface Modulation of PdCu Nanocatalysts Via the Crystal Structure Change for Lithium-Oxygen Battereis
Authors: Park Mihui , Liang Chaoping , Adjei Agyeman Daniel , Cho Kyeongjae , Kang Yong-Mook
Published: February 2020

Palladium-copper (PdCu) alloys have two representative crystal structures; one is body-centered cubic (bcc), the other is face-centered cubic (fcc) even though both Pd and Cu originally have fcc crystal. The fcc PdCu alloys have disordered structure within which Pd and Cu have solid-solution in fcc lattice, whereas the bcc PdCu alloys have ordered structure which consists of alternative layers with either Pd or Cu atoms.

In particular, bcc PdCu alloys have occasionally shown superior performance to fcc PdCu alloys since the unique ordered structure of bcc has isolated Pd on the surface. Most of bcc PdCu alloys have been synthesized for structural transformation by annealing or seed-growth method of fcc PdCu alloys with inevitable grain growth, uneven surface structure and particle size distribution. Despite these limitations, the Pd on the bcc surface which is provided charge flow from Cu serves as an active site for catalytic reaction, which is highly favorable for lithium-oxygen battery. However, the same size of fcc and bcc PdCu alloys is quite difficult to be obtained since the crystallites larger than 20 nm favor the ordered bcc structure with lower symmetry. Thus, bcc PdCu alloys in nanoscale have been rarely reported, consequently fcc and bcc PdCu nanoparticles (NPs) have never been properly compared until now.

In this study, we successfully synthesize fcc and bcc PdCu alloys in nanoscale through precisely adjusting the driving force for reducing organometallic complex. The bcc PdCu NPs with higher surface energy govern the growth thermodynamics of discharge product and greatly improved battery performance based on density functional theory calculation and experimental proof. This study provides critical descriptor on material design in the perspective of modulating surface structure via crystal structure to tune its intrinsic properties.
Thermal-Runaway-Free Lithium Ion Battery Cell
Authors: Qiao Yu , Wang Meng , Yi Haozhe
Published: February 2020

For large-format high-energy lithium-ion battery (LIB), formation of internal short circuit (ISC) often results in catastrophic thermal runaway, leading to fire and/or explosion. It imposes touch challenges to system safety and robustness for electric vehicles, personal electronics, large-scale energy storage systems, to name a few. It is desirable to prevent thermal runaway at the electrodes level, through cell engineering.

Recently, we developed “super-safe” LIB cells with functional current collectors (FCC). Independent of the active materials layers, FCC contains physical features that can favorably control the damage mode of electrodes. Once ISC is formed, FCC works as an effective “fuse” that shuts down the internal short current immediately, before heat generation even begins.

The advantages of FCC include:

FCC is highly effective. Our experiments on FCC-based pouch cells showed only mild temperature increase upon severe impact penetration of metal; reference cells exploded instantaneously under the same abuse testing condition.

FCC does not affect the cell cycle life, since the thermal runaway mitigation process is non-chemical and decoupled from the electrochemical reactions.

FCC does not affect the mass production of active materials and other cell components. The failsafe mechanisms are carried entirely by the current collectors.

Similar FCC technique can be applied to a wide variety of battery chemistries, including future high-energy batteries.

FCC adds little mass or volume to battery cell, and is cost efficient.

FCC can be produced through a roll-to-roll procedure.
Studies of Rollover Failure in Lithium-Ion Cells
Authors: Ma Xiaowei , Harlow Jessie , Keefe Alison S , Li Jing , Glazier Stephen , Ma Lin , Hall David S , Aiken Connor P , Genovese Matthew , Cormier Marc , Dahn Jeff R
Published: February 2020

Sometimes lithium-ion cells show a very insidious type of failure where they display close to 100% of their capacity for about 1000 charge-discharge cycles and then lose most of their capacity in only 100 cycles or so with very little warning to the user. This is called “rollover failure” [1]. Experimental observations show that the likelihood of rollover failure increases with upper cut-off potential of lithium-ion cells and decreases with LiPF6 concentration in a reasonable range.

Since increasing the upper cut-off potential is essential to increase the energy density of lithium-ion cells, a full understanding of the causes of rollover failure is essential, but this is proving very difficult to attain.

The phenomenon of rollover failure during long-term cycling will be discussed based on a comparison among Li(Ni0.5Mn0.3Co0.2)O2/graphite pouch cells with different electrolyte and electrode designs undergoing different testing protocols. A few facts can be gleaned from the data:

For cells charged to the same upper cut-off potential, those showing the highest rates of electrolyte oxidation at the positive electrode (due to electrolyte or cell chemistry changes) are most prone to rollover failure.

Any cell is more prone to rollover failure if charged to a higher potential. This increases the rate of electrolyte oxidation at the positive electrode.

When rollover occurs, the impedance at the positive electrode always increases significantly while the impedance at the negative electrode side is relatively stable.

Lithium metal plating at the negative graphite electrode surface is not always observed during the initial stages of rollover failure.

Increasing the LiPF6 concentration properly can delay the occurrence of rollover failure. For example Figure 1 shows the impact of increasing salt concentration from 1.2 M to 1.5 M.

Based on these and other observations, some simple models that integrate electrolyte oxidation, impedance growth and lithium ion diffusion can be postulated but further experimental studies using a variety of methods are required for full understanding.

[1] J. C. Burns, A. Kassam, N. N. Sinha, L. E. Downie, L. Solnickova, B. M. Way, J. R. Dahn, J. Electrochem. Soc., 160, A1451-A1456 (2013).

Figure 1. Capacity (top panels), normalized capacity (middle panels) and ΔV (bottom panels) versus cycles of Li[Ni0.5Mn0.3Co0.2]O2/graphite pouch cells filled with 1.2 M LiPF6 or 1.5 M LiPF6 in EC:EMC:DMC (25:5:70 vol.%) and 2 wt.%VC+1 wt.%DTD. Cycling was performed between 3V and 4.1V or 4.3V at 20 oC with charging/discharging rates at 1C/1C.

Figure 1
Effect of Processing Route and Dopant on Capacity/Fading of Layered Oxide Cathode
Authors: Fung Kuan-Zong , Fung Kenneth , Yang Hui-Ju , Chang Chia Chin , Tsai Shu-Yi
Published: February 2020

Although several crystal structures have been demonstrated and shown reversible capabilities during lithiation/delithiation processes in cathode of Li ion batteries; oxides with layered structure still remain the ones that provide higher capacities.

However, higher charging capacity means the creation of more ionic/electronic defects in both cation and/or anion sublattices of layered structure. Higher defect concentration in either cation or anion sublattices tend to destabilize its crystal structure. As a result, the phase change is frequently observed in repeatedly cycled cathode. Furthermore, the phase-changing layered cathode tends to show the capacity fading after cycling tests. Based on defect consideration, the stability of highly defective materials may be enhanced by using dopant and/or better processing control. In this study, the electrical/electrochemical/structural properties of NMC 811 and LiNi0.8Co0.15Al0.05 will be investigated. Since Ni content is fixed at 80% in the transition metal ion layers in these cathode materials, the variation in electrochemical properties will be caused by the minor elements/dopants such as Mn and Al. First, the electrical measurement of NMC 811 and LiNi0.8Co0.15Al0.05 are conducted using sintered disc. Assembled cells using above-mentioned cathode and Li anode with desired liquid electrolyte will be tested and cycled. XPS, SEM and XRD analyses will be conducted on as-assembled as well as cycled cells. The analyzing results will be illustrated based on the chemical characteristics of doping ions and the accompanying defects created.
The Underlying Cause of Low Coulombic Efficiency in Li Metal Batteries and Mitigation Strategies
Authors: Fang Chengcheng , Zhang Yihui , Lee Jungwoo Z. , Yang Yangyuchen , Yang Fan , Alvarado Judith , Schroeder Marshall A. , Yang Li , Cai Mei , Gu Jing , Xu Kang C. , Wang Xuefeng , Meng Ying Shirley
Published: February 2020

Lithium metal batteries have high energy density but suffer from the capacity loss and short cycle life due to the formation of electrochemically inactive Li, which consists of Li
+ contained in solid electrolyte interface (SEI) and unreacted metallic Li0. Exactly Li+ or Li0 is dominant to the capacity loss has long been debated due to the challenges in accurately differentiating and quantifying Li+ in SEI and inactive metallic Li0 amount. Here, we introduce a new analytic method to accurately distinguish and quantify the contribution from metallic Li0 to total amount of the inactive Li. We uncover that the metallic Li0 is the major cause of low Coulombic efficiency, rather than the electrochemically formed SEI. Using cryogenic electron microscopies to further study the microstructure and nanostructure of inactive Li, we find that the unreacted metallic Li0 is indeed wrapped by insulating SEI, losing the electronic conductive pathway. Coupling the measurement of global content of metallic Li0 to observations of its local nanostructure, we reveal the formation mechanism of inactive Li in different types of electrolytes, identifying the true underlying cause of low efficiency in Li metal deposition and stripping. we ultimately propose strategies to enable highly efficient metallic Li deposition and stripping to enable Li metal anode for next generation batteries.
(Invited) Design of the Separators for Li-Ion and Lithium Metal Batteries
Authors: Edström Kristina , Pan Ruijun , Wang Zhaohui , Strømme Maria , Nyholm Leif
Published: February 2020

Functionalization of separators is one path to increase the performance of Li-ion (LIB) and lithium metal batteries (LMB). This is a research area within LIBs not very extensively explored. A separator should prevent direct contact between the positive and negative electrodes and provide good ionic transport pathways. Commercial separators are usually made of polyolefin with low thermal stability and low electrolyte wettability. In this study, cellulose of a green algae has been used to make new separator materials via a simple paper making method. The resulting separator material has several advantages compared to commercial separator materials in ionic conductivity, thermal stability, electrolyte wettability and type of pore distribution. With this material as the basis two types of advanced separator functionalities was designed and will be described in the presentation. 1) Redox-active separators based on the use of a redox-active conducting polymer, polypyrrole (PPy) and a natural polymer, polydopamine (PDA) where the PPy-based redox-active separator is designed to contribute capacity to the cathode of a LIB, while the PDA-based redox-active separator is proposed to be used on the anode side. 2) It is known that a homogeneous current distribution is beneficial for the battery performance. Therefore, separators with homogenous pore distributions have been manufactured to study the influence of the pore distribution on the Li deposition/stripping behavior and composite cathode utilization in LMBs. One example is a sandwich-structured separator composed of two cellulose nanofiber (CNF) surface layers and an intermediate glass microfiber (GMF) and then a CNF composite layer on the other side. The CNF surface layers, of the sandwich-separator, have homogeneous distribution of nano-sized pores, which favours a homogeneous current distribution at both electrodes. The intermediate GMF/CNF layer, however, has excellent ionic transport due to a macro porous structure of the material. This separator exhibits a good electrolyte wettability and better thermal stability compared to a classical Celgard separator. The reason for this is the use of the hydrophilic and thermally stable CNFs and GMFs. The combination of nano-sized and micro-sized fibers used in this separator yields a higher ionic conductivity than that for the commercial separator (1.14 vs. 0.49 mS cm−1). The performance is studied for both Li anodes and LiFePO4 composite cathodes and the results show that use of separators with high porosities and homogeneous surface pore distributions can improve the performances (e.g. capacities and stabilities) of LMBs considerably. The presentation will highlight the importance of proper separator/electrode interactions. The present approach constitutes a practical engineering strategy for the production of separators with nano/micro fibers and a promising route for the development of LMBs with improved safety and enhanced electrochemical performances.
Three-Dimensional Porous Si with in Situ Decorated Carbon Nanotubes As Anode Materials for Li-Ion Batteries
Authors: Su Junming , Huang Tao , Yu Aishui
Published: February 2020

Rechargeable Li-ion Batteries have been widely used as energy storage devices for portable electronics owing to their higher energy density and long cycle life. However, higher capacity cathode and anode materials are required for their large-scale application in electrical vehicles (EVs)[1-3]. Currently, commercialized Li-ion batteries with graphite as an anode material are still far from practical use in EVs because of their limited capacity and unsatisfactory cycling performance. Many anode materials with higher theoretical capacities have been proposed. Among them, silicon is more attractive because of its highest theoretical specific capacity (~4200 mAh/g), low redox potential (< 0.5 V versus Li/Li+), and abundance as a mineral resource[4-5]. However, silicon has two main defects: low electronic conductivity and very large volume changes (~300%) during lithiation/delithiation. In this work, we prepared three-dimensional porous Si with in situ decorated carbon nanotubes. Si clusters were obtained from commercial Al-Si alloy spheres by pickling aluminum component. Then, carbon nanotubes were in situ grown on Si cluster by a chemical vapor deposition (CVD) process using toluene as a carbon source and Ni particles as a catalyst. The obtained material was denoted as Si cluster/CNTs. For comparison, Si cluster coated with carbon layers by the same CVD process without Ni catalyst was also prepared, denoted as Si cluster/C. The electrochemical results demonstrated that Si cluster/CNTs had longer life and higher rate cycling performance (2000 mAh g-1 at 0.5 A g-1 after 250 cycles) than Si cluster and Si cluster/C. The cluster structure could effectively relieve the volumetric change during charge-discharge process. The carbon nanotubes could improve the electronic conductivity and stabilize the structure of Si cluster in Si cluster/CNTs.

References

[1] Park, M.-H.; Kim, M. G.; Joo, J.; Kim, K.; Kim, J.; Ahn, S.; Cui, Y.; Cho, J. Nano Lett. 2009, 9, 3844−3847.

[2] Goodenough, J. B.; Kim, Y. Challenges for Rechargeable Li Batteries. Chem. Mater. 2010, 22, 587−603.

[3] Zuo, X.-X, Zhu, J., Muller-Buschbaum, P., Cheng, Y.-J., Nano Energy, 2017, 31, 113-143

[4] Zhou, M.; Cai, T.; Pu, F.; Chen, H.; Wang, Z.; Zhang, H.; Guan,S. ACS Appl. Mater. Interfaces 2013, 5, 3449−3455.

[5] Szczech, J. R.; Jin, S., Energy Environ. Sci. 2011, 4, 56−72.
(Invited) Generation and Evolution of Materials in the Anode Solid Electrolyte Interphase (SEI) of Lithium Ion Batteries
Authors: Lucht Brett
Published: February 2020

A solid electrolyte interphase is generated on the anode of lithium ion batteries during the first few charging cycles. The presence and stability of the solid electrolyte interphase (SEI) is critical to the performance of the battery. Despite thorough investigation of the SEI for over 20 years, the mechanism of formation and function are still relatively poorly understood. We have investigated the structure of the initial SEI on graphite and silicon electrodes along with changes which occur to the SEI upon additional cycling via a combination of ex-situ surface analysis techniques. The investigation of SEI provides significant insight into the structure and properties of the anode SEI.

The one electron reducing agent, lithium napthalenide has been used to independently prepare the reduction products which constitute the SEI. The initial reduction product of ethylene carbonate is lithium ethylene dicarbonate (LEDC). However, the thermal decomposition of LEDC and related lithium alkyl carbonates in the presence of LiPF6 generates a intricate mixture of compounds which greatly complicates the structure of the SEI. The reduction products and their subsequent thermal decomposition products have been thoroughly investigated via a combination of NMR, XPS, IR-ATR, TGA, and GC-MS. Mechanisms for the generation of the complicated mixture of products will be discussed.

Thermal behavior of the SEI on a silicon electrode for Lithium ion batteries has been investigated by TGA. In order to provide a better understanding of the thermal decomposition of the SEI on silicon, the thermal decomposition behavior of independently synthesized lithium ethylene dicarbonate (LEDC) was investigated as a model SEI. The model SEI (LEDC) has three stages of thermal decomposition. Over the temperature range of 50~300oC, LEDC decomposes to evolve CO2 and C2H4 gasses leaving lithium propanoate (CH3CH2CO2Li) and Li2CO3 as solid residues. The lithium propanoate decomposes over the temperature range of 300~600oC to evolve pentanone leaving Li2CO3 as a residual solid. Finally, the Li2CO3 decomposes over 600oC to evolve CO2 leaving Li2O as a residual solid. A very similar thermal decomposition process is observed for the SEI generated on cycled silicon electrodes. However, two additional thermal decomposition reactions were observed characteristic of LixPOyFz at 300oC and the polyimide binder at 550oC. TGA measurements of Si electrodes after various numbers of cycles suggest that the LEDC on Si electrodes thermally decomposes during cycling to form lithium propanoate and Li2CO3, resulting in increased complexity of the SEI.
Effect of Li2MnO3 Performance on Electrochemical Properties of Li-Rich Composite Layered Cathode
Authors: Fung Kuan-Zong , Tsai Shu-Yi , Chang Li-Fu , Liu Chi-Yang
Published: February 2020

Composite layered cathode materials formulated as xLi2MnO3-(1-x)LiMO2(M = Mn, Ni, Co, etc.) show their surprisingly high reversible capacity and have received much attention for Li-ion battery applications. It is known that Li2MnO3 has played important role of providing extra Li source for stabilizing the layered structure. However, single phase Li2MnO3 has shown very limited capacity during charging/discharging reaction. Very interestingly, there is a characteristic 1st charging plateau corresponding to the extended capacity contribution from oxygen oxidation in Li2MnO3. Furthermore, such oxygen oxidation also causes the formation of oxygen defects (vacancies) and may cause the subsequent capacity fading. In order to obtain a stable and high capacity Li-rich composite oxides cathode with layered structure, it is important to investigate and to improve the electrochemical properties of Li2MnO3 with a systematic study. Therefore, the main objective of this study is (i) to modify the defect structure of Li2MnO3 through changing oxygen partial pressure during synthesis, (ii) to use dopants to introduce more electrons to Li2MnO3 for better electronic conduction, (iii) to assemble and test cells using Li2MnO3 as the cathode and Li metal as the anode, (iv) to characterize and understand the electrochemical properties of Li2MnO3 that are under various treatments.

In this study, Li2MnO3 are prepared using sol gel process and followed by treatment with different atmospheres. Proper dopants with various concentrations will be added into Li2MnO3 for enhanced conduction and better stability. Impedance of Li2MnO3 will be measured using Electrochemical Impedance Spectroscopy (EIS). XRD analysis and SEM observation will be performed for synthesized Li2MnO3 particles. A full cell based on Li/ Li2MnO3 and Li/ 0.5Li2MnO3-0.5LiMO2 using treated or doped Li2MnO3 will be assembled and tested.
(Invited) Mitigating Oxygen Release in Anionic-Redox-Active Cathode Materials By Cationic Substitution through Rational Design
Authors: Meng Ying Shirley
Published: February 2020

In classical layered oxide cathodes, when substituting excess amount of lithium in the transition metal layer, oxygen extends its role as a structural framework, exhibiting electrochemical activity and enhancing the reversible capacities of layered oxides through anionic redox mechanisms. Nevertheless, if unoptimized, oxygen activity comes with instability in the form of oxygen loss, which is associated with irreversible voltage decay and capacity fade. To understand this irreversible loss and to increase the stability of lattice oxygen, density functional theory is applied to calculate oxygen vacancy formation energies in lithium rich transition metal layered oxides for a variety of dopants, noting increased stability upon doping with 4d elements Mo and Ru. Driven by these findings, Mo is co-doped with Co into Li[Li0.2Ni0.2Mn0.6]O2, showing notably reduced voltage decay and capacity fade without sacrificing energy density and cycle life, and evidence of Mo incorporation is presented. Calculations suggest this is due to a modified charge density distribution around anions upon incorporation of Mo, altering local band structure and impeding oxygen vacancy formation, while maintaining the anionic activity available for redox. We will demonstrate the other possible strategies to mitigate the oxygen loss in anion redox cathode materials for next generation lithium ion batteries.
Metal-Ion Batteries Based on New Copper and Nickel Coordination Polymers with Aromatic Polyamine Ligands
Authors: Kapaev Roman R. , Stevenson Keith J. , Troshin Pavel A.
Published: February 2020

Redox-active materials with high electron and ion conductivities are required for the new generation of metal-ion batteries (MIBs) with high energy density and high rate capability. Recently, a novel family of conductive (>1 S/cm) and electrochemically active metal organic frameworks (MOFs) composed of aryl amine ligands and bivalent transition metal ions (Cu2+, Ni2+, Co2+) has been reported. However, this class of MOFs remains virtually unexplored in metal-ion batteries. In particular, the only structures tested in MIBs are based on hexaaminobenzene, a molecule that readily decomposes or gets oxidized during synthesis or while handling, which limits its applicability.

Here we report new Ni(II) and Cu(II) coordination polymers derived from commercially available or easily synthesizable polyamines, e.g. 1,2,4,5-tetraaminobenzene tetrahydrochloride (TAB*4HCl), etc. A series of target MOFs was synthesized by simply mixing the ligand and the transition metal salt in the presence of air and ammonia. The novel materials are characterized using a set of complementary techniques including solid-state NMR, elemental analysis, IR spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and electron microscopy. Their electrochemical behavior is rationalized using impedance spectroscopy monitoring and ex situ XPS.

The obtained MOFs were successfully applied as both cathode and anode materials in lithium- and sodium-ion batteries and demonstrated ultra-high rate capability and stability. For example, a specific capacity of 83 mAh/g can be reached for the Ni(II) polymer derived from TAB*4HCl at 20 A/g current rate (>250 C) in 0.8-2.0 V vs. Li/Li+ range, while 79% of this capacity is retained after 20000 cycles. Another example is the Cu-TAB coordination polymer, which shows a specific capacity up to 262 mAh/g in 1.5-4.1 V vs. Li/Li+ range, which corresponds to the energy density of 616 Wh/kg.

The revealed correlations between the molecular structures of MOFs, their physicochemical properties and electrochemical performance pave a way to rational design of new coordination polymers for advanced metal-ion batteries.