Interface Investigations of a Commercial Lithium Ion Battery Graphite Anode Material by Sputter Depth Profile X‑ray Photoelectron Spectroscopy

Here we provide a detailed X-ray photoelectron spectroscopy (XPS) study of the electrode/electrolyte interface of a graphite anode from commercial NMC/graphite cells by intense sputter depth profiling using a polyatomic ion gun. The uniqueness of this method lies in the approach using 13-step sputter depth profiling (SDP) to obtain a detailed model of the film structure, which forms at the electrode/electrolyte interface often noted as the solid electrolyte interphase (SEI). In addition to the 13-step SDP, several reference experiments of the untreated anode before formation with and without electrolyte were carried out to support the interpretation. Within this work, it is shown that through charging effects during X-ray beam exposure chemical components cannot be determined by the binding energy (BE) values only, and in addition, that quantification by sputter rates is complicated for composite electrodes. A rough estimation of the SEI thickness was carried out by using the LiF and graphite signals as internal references

Different Efforts but Similar Insights in Battery R&D: Electrochemical Impedance Spectroscopy <i>vs</i> Galvanostatic (Constant Current) Technique

Electrochemical impedance spectroscopy (EIS) using alternating currents is a widely established technique to investigate kinetic aspects of batteries and their components, though it requires an interruption of battery operation with extra measurement time and effort. In this work, EIS is compared with the conventional galvanostatic (constant current) technique, which is based on direct currents, being the standard operation mode of batteries. Data from constant current measurements not only are representing application conditions but also are automatically and continuously generated during routine charge/discharge processes, i.e., without extra measurement efforts, and do give kinetic insights via the characteristic overvoltage (= resistance-reasoned voltage rise/decrease), as well. In fact, distinguishing between even very similar values for ohmic (RΩ), charge transfer (Rct), and mass transport (Rmt) resistances can be done via analysis of overvoltage data from constant current measurements, as exemplarily demonstrated in symmetric Li||Li and LiNi0.6Mn0.2Co0.2O2 (NMC622)||Li cells with poly(ethylene oxide)-based solid polymer electrolyte, finally proving their validity. From a practical point of view, direct-current methods can be beneficial for R&D of kinetic aspects in batteries, as data is directly obtained and, thus, application-oriented

Invasive species influence macroinvertebrate biomonitoring tools and functional diversity in British rivers

Biological invasions could have major implications for the management and conservation of freshwater systems if they lead to a misclassification of waterbodies. However, there is limited understanding of the sensitivity of existing biomonitoring tools to invasive species in rivers; and even less known regarding how they influence community taxonomic and functional measures. This research explores the response of freshwater macroinvertebrate communities to biological invasion using taxonomic and functional indices. Utilising a long-term dataset (spanning 2000–2019, 5,988 samples) from rivers in England, the performance of four biomonitoring tools (WHPT, WHPT-ASPT, LIFE and PSI) and two community functional indices (functional richness and redundancy) was examined before and after the colonisation of the invasive species, Dikerogammarus haemobaphes (Eichwald, 1841; Crustacea: Gammaridae). This species represents a recent (first record 2012) and highly successful invader, allowing its range expansion within waterbodies to be examined in detail. Spatial (national and basin level) and seasonal (spring and autumn) effects were investigated using a before–after control–impact (BACI) experimental framework and linear mixed effects models. Results indicated that invasion by D. haemobaphes resulted in significant reductions to the WHPT index and functional diversity metrics (richness and redundancy) while more subtle patterns were observed for other metrics. Analysis of seasonal and individual river basins (River Trent and R. Thames) identified largely consistent responses. The establishment of D. haemobaphes also resulted in some modifications to the functional composition of aquatic communities primarily associated with voltinism and resistance features. Synthesis and applications. Our findings indicate that Dikerogammarus haemobaphes should be considered a significant pressure to riverine communities. These results have implications for biomonitoring, which informs managerial actions as effects may not be detected using a single taxonomic index. Community functional measures are useful in characterising the effects of invasive species and may form a valuable part of the ‘toolbox’ used for studying biological invasions in rivers. The research illustrates the need to consider the wider threats posed by invasive species on the long-term integrity of freshwaters and the efficacy of freshwater biomonitoring tools

Supramolecular Self-Assembly of Methylated Rotaxanes for Solid Polymer Electrolyte Application

Li⁺-conducting solid polymer electrolytes (SPEs) obtained from supramolecular self-assembly of trimethylated cyclodextrin (TMCD), poly­(ethylene oxide) (PEO), and lithium salt are investigated for application in lithium-metal batteries (LMBs) and lithium-ion batteries (LIBs). The considered electrolytes comprise nanochannels for fast lithium-ion transport formed by CD threaded on PEO chains. It is demonstrated that tailored modification of CD beneficially influences the structure and transport properties of solid polymer electrolytes, thereby enabling their application in LMBs. Molecular dynamics (MD) simulation and experimental data reveal that modification of CDs shifts the steady state between lithium ions inside and outside the channels, in this way improving the achievable ionic conductivity. Notably, the designed SPEs facilitated galvanostatic cycling in LMBs at fast charging and discharging rates for more than 200 cycles and high Coulombic efficiency

Failure Mechanisms at the Interfaces between Lithium Metal Electrodes and a Single-Ion Conducting Polymer Gel Electrolyte

Polymer electrolytes have the potential to enable rechargeable lithium (Li) metal batteries. However, growth of nonuniform high surface area Li still occurs frequently and eventually leads to a short-circuit. In this study, a single-ion conducting polymer gel electrolyte is operated at room temperature in symmetric Li||Li cells. We use X-ray microtomography and electrochemical impedance spectroscopy (EIS) to study the cells. In separate experiments, cells were cycled at current densities of 0.1 and 0.3 mA cm–2 and short-circuits were obtained eventually after an average of approximately 240 cycles and 30 cycles, respectively. EIS reveals an initially decreasing interfacial resistance associated with electrodeposition of nonuniform Li protrusions and the concomitant increase in electrode surface area. X-ray microtomography images show that many of the nonuniform Li deposits at 0.1 mA cm–2 are related to the presence of impurities in both electrolyte and electrode phases. Protrusions are globular when they are close to electrolyte impurities but are moss-like when they appear near the impurities in the lithium metal. At long times, the interfacial resistance increases, perhaps due to additional impedance due to the formation of additional solid electrolyte interface (SEI) at the growing protrusions until the cells short. At 0.3 mA cm–2, large regions of the electrode–electrolyte interface are covered with mossy deposits. EIS reveals a decreasing interfacial resistance due to the increase in interfacial area up to short-circuit; the increase in interfacial impedance observed at the low current density is not observed. The results emphasize the importance of pure surfaces and materials on the microscopic scale and suggest that modification of interfaces and electrolyte may be necessary to enable uniform Li electrodeposition at high current densities

Toward Na-ion BatteriesSynthesis and Characterization of a Novel High Capacity Na Ion Intercalation Material

The rapid growth of the worldwide demand of lithium for batteries (LIBs) can possibly lead to a shortage of its reserves. Sodium batteries represent a promising alternative because they enable much higher energy densities than other battery systems, with the exception of LIBs, and are not limited by sodium availability. Herein, we present a novel, Na⁺ ion intercalation material, Na_0.45Ni_0.22Co_0.11Mn_0.66O₂ (space group <i>P</i>6₃/<i>mmc</i>) synthesized in air by a coprecipitation method followed by a thermal treatment and a water-rinsing step. This material performs a specific capacity of 135 mA h g^–1 with a Coulombic efficiency exceeding 99.7%. Upon long-term cycling tests the material shows excellent capacity retention after more than 250 cycles. Such an overall performance, superior to that of presently known sodium-ion cathodes, represents a step further toward the realization of sustainable batteries for efficient stationary energy storage

Highly Effective Solid Electrolyte Interphase-Forming Electrolyte Additive Enabling High Voltage Lithium-Ion Batteries

The electrochemical and thermal stabilities of commonly used LiPF₆/organic carbonate-based electrolytes are still a bottleneck for the development of high energy density lithium-ion batteries (LIBs) operating at elevated cell voltage and elevated temperature. The use of intrinsic electrochemically stable electrolyte solvents, e.g. sulfones or dinitriles, has been reported as one approach to enable high voltage LIBs. However, the major challenge of these solvents is related to their poor reductive stability and lack of solid electrolyte interphase (SEI)-forming ability on the graphite electrode. Here, 3-methyl-1,4,2-dioxazol-5-one (MDO) is synthesized and investigated as new highly effective SEI-forming electrolyte additive which can sufficiently suppress electrolyte reduction and graphite exfoliation in propylene carbonate (PC)-based electrolytes. With the addition of only 2 wt % MDO, LiNi_0.5Mn_0.3Co_0.2O₂ (NMC532)/graphite full cells containing a 1 M LiPF₆ in PC electrolyte reach a cycle life of more than 450 cycles while still having a capacity retention of 80%. In addition, MDO has proven to be oxidatively stable until potentials as high as 5.3 V vs Li/Li⁺. Further development of MDO and its derivatives as electrolyte additives is a step forward to high voltage stable electrolyte formulations based on alternative electrolyte solvents and high energy density LIBs

Supplemental_Material – Supplemental material for Automated MALDI Target Preparation Concept

<p>Supplemental material, Supplemental_Material for Automated MALDI Target Preparation Concept by Martin Winter, Robert Ries, Carola Kleiner, Daniel Bischoff, Andreas H. Luippold, Tom Bretschneider and Frank H. Büttner in SLAS Technology</p

Supplemental_Table_S1 – Supplemental material for Automated MALDI Target Preparation Concept

<p>Supplemental material, Supplemental_Table_S1 for Automated MALDI Target Preparation Concept by Martin Winter, Robert Ries, Carola Kleiner, Daniel Bischoff, Andreas H. Luippold, Tom Bretschneider and Frank H. Büttner in SLAS Technology</p

In Situ Diffuse Reflectance Infrared Fourier-Transform Spectroscopy Investigation of Fluoroethylene Carbonate and Lithium Difluorophosphate Dual Additives in SEI Formation over Cu Anode

The synergetic effect of fluoroethylene carbonate (FEC) and lithium difluorophosphate (LiPO2F2) dual additives on the cycling stability of lithium metal batteries has been previously reported. This study applies in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) to examine the impact of these two additives on SEI species formation over Cu anode using a base electrolyte of LiPF6 in ethylene carbonate (EC) and diethyl carbonate (DEC). The results indicate that all electrolyte components and additives can be electrochemically reduced over the Cu anode following a potential sequence of LiPO2F2 > FEC > EC > DEC. The results illustrate that LiPF6 likely interacts with the Cu anode upon contact, resulting in LixPFy, which can lead to a reduction peak at ∼1.44 V in CV. With the base electrolyte, reduced species from LixPFy lead to the formation of alkyl phosphorus fluorides (RPF), which can be suppressed by the presence of FEC and/or LiPO2F2. Similar to previous reports, FEC reduction in the 1st lithiation cycle leads to the continuous formation of poly(FEC), while EC is electrochemically reduced to (CH2OCO2Li)2 and Li2CO3 and DEC is reduced to CH3CH2OCO2Li and Li2CO3. With only the LiPO2F2 additive, the redox of LiPO2F2 can be found in CV with LixPOy as the possible reduced product. In addition, Li2CO3 formation from EC and DEC reduction was relatively suppressed by the presence of LiPO2F2. The simultaneous presence of the FEC additive can suppress the redox of LiPO2F2 and partly the decomposition of LiPF6 likely via the preferential adsorption of FEC on Cu. Similar DRIFTS observations are found over the Li anode. The electrolyte with dual additives demonstrates a possible advantage from poly(FEC) and LixPOy species formation, suppressing the reduction of LixPFy, EC, and DEC though not completely