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Understanding aging phenomena in batteries is crucial to the design of efficient, safe, and reliable energy storage devices as a part of the current green energy transition. Among the different aspects of a battery, the behavior of the electrolyte is a key parameter. Therefore, screening the aging characteristics of different electrolytes is of major interest. However, few screening studies exist because these are time‐consuming and require the monitoring of numerous charge and discharge cycles. It has been demonstrated here that radiation chemistry, i.e., the interaction between ionizing radiation and matter, is a valuable tool to screen the behavior of various electrolytes within a few hours. Indeed, the rapid radiolysis of electrolytes leads to the production of the same gases as produced by electrochemical cycling (i.e., H2, CO2), and the ranking of electrolytes by their H2 production yields similar performance ratings to those reported in the literature. Therefore, this direct comparison of electrolytes alone, lasting a few hours without any manufacturing operations such as the fabrication of electrochemical cells, demonstrates that controlled irradiation makes it possible to predict battery cycling behavior. Additionally, mechanisms involved in the degradation processes of different electrolytes are proposed. [ABSTRACT FROM AUTHOR]

In recent decades, rechargeable Mg batteries (RMBs) technologies have attracted much attention because the use of thin Mg foil anodes may enable development of high‐energy‐density batteries. One of the most critical challenges for RMBs is finding suitable electrolyte solutions that enable efficient and reversible Mg cells operation. Most RMB studies concentrate on the development of novel electrolyte systems, while only few studies have focused on the practical feasibility of using pure metallic Mg as the anode material. Pure Mg metal anodes have been demonstrated to be useful in studying the fundamentals of nonaqueous Mg electrochemistry. However, pure Mg metal may not be suitable for mass production of ultrathin foils (<100 microns) due to its limited ductility. The metals industry overcomes this problem by using ductile Mg alloys. Herein, the feasibility of processing ultrathin Mg anodes in electrochemical cells was demonstrated by using AZ31 Mg alloys (3 % Al; 1 % Zn). Thin‐film Mg AZ31 anodes presented reversible Mg dissolution and deposition behavior in complex ethereal Mg electrolytes solutions that was comparable to that of pure Mg foils. Moreover, it was demonstrated that secondary Mg battery prototypes comprising ultrathin AZ31 Mg alloy anodes (≈25 μm thick) and MgxMo6S8 Chevrel‐phase cathodes exhibited cycling performance equal to that of similar cells containing thicker pure Mg foil anodes. The possibility of using ultrathin processable Mg metal anodes is an important step in the realization of rechargeable Mg batteries. [ABSTRACT FROM AUTHOR]

This paper deals with the occurrence of a graphite irreversible degradation mechanism in commercial Graphite (C) / lithium Nickel Manganese Cobalt oxide (NMC) lithium-ion batteries, challenging metallic lithium deposition as the major aging mechanism at low temperature cycling. In this study, commercial 16 Ah C/NMC Li-ion cells were aged during cycling at 5°C at a rate of 1C between 2.7 V and 4.2 V (namely between 0 and 100% of state of charge (SOC), respectively), with significant performance fading after 50 cycles only, while up to 4000 cycles can be performed at 45°C with the same commercial cells. The monitoring of the potential of each electrode during cycling has been performed through the successful introduction of lithium metal as reference electrode into the commercial cell. This technique demonstrated that it was more and more difficult to extract lithium ions from graphite particles to intercalate into the positive electrode as the number of cycles increased. Graphite electrodes remained unexpectedly lithiated after cells were dismantled in discharged state. A part of exchangeable lithium detected being trapped into the negative electrode as graphite intercalation compounds was observed with X-Ray Diffraction (XRD). Lithium-7 Nuclear Magnetic Resonance (7Li NMR) performed on graphite electrode led to the distinction between lithium intercalated into graphite, oxidized lithium in the Solid Electrolyte Interphase (SEI) and metallic lithium present in low amounts. Coupling Focused Ion Beam (FIB) / Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Photoelectron Spectrometry (XPS) techniques demonstrated the presence of an untypical layer composed of electrolyte degradation products, hindering graphite electrode pores, particularly concentrated in the regions corresponding to interparticle cavities where lithium was found enriched and trapped. [ABSTRACT FROM AUTHOR]

Metallic lithium deposition is a typical aging mechanism observed in lithium-ion cells at low temperature and/or at high charge rate. Lithium dendrite growth not only leads to strong capacity fading, it also causes safety concerns such as short-circuits in the cell. In applications such as electric vehicles, the use of lithium-ion batteries combines discharging, long rest time and charging phases. It is foremost a matter of lifetime and safety from the perspective of the consumer or the investor. This study presents the post-mortem analyses of commercial 16 Ah Graphite/NMC (Nickel Manganese Cobalt layered oxide) Li-ion pouch cells. The cells were degraded by calendar aging at high temperature with or without periodic capacity tests. Unexpected local depositions of metallic lithium were confirmed on graphite electrodes by Nuclear Magnetic Resonance (NMR). Biphenyl, a monomer additive present in the liquid electrolyte, generates gas during its polymerization reaction occurring at high temperature and at high state of charge. As a result, dry-out areas are present between the electrodes leading to high impedance regions and no charge transfer between the electrodes. It is at the border of these areas that lithium metal is deposited. [ABSTRACT FROM AUTHOR]

The ageing phenomena occurring in various diethyl carbonate/LiPF6 solutions are studied using gamma and pulse radiolysis as a tool to generate similar species as the ones occurring in electrolysis of Li-ion batteries (LIBs). According to picosecond pulse radiolysis experiments, the reaction of the electron with (Li+, PF6−) is ultrafast, leading to the formation of fluoride anions that can then precipitate into LiF(s). Moreover, direct radiation-matter interaction with the salt produces reactive fluorine atoms forming HF(g) and C2H5F(g). The strong Lewis acid PF5 is also formed. This species then forms various R1R2R3P=O molecules, where R is mainly −F, −OH, and −OC2H5. Substitution reactions take place and oligomers are slowly formed. Similar results were obtained in the ageing of an electrochemical cell filled with the same model solution. This study demonstrates that radiolysis enables a description of the reactivity in LIBs from the picosecond timescale until a few days. [ABSTRACT FROM AUTHOR]

A quantitative analysis of in situ and operando X‐ray diffraction studies allows for deeper insight into the mechanism of Li2S formation and consumption. A two‐step reaction process is proposed for both discharge and charge. Changing selectivity for Li2S formation is estimated, with solely Li2S being formed during the earliest step, followed by possible concurrent formation of Li2S2 intermediate in the further step of discharge. [ABSTRACT FROM AUTHOR]

Abstract: The formation and the evolution of lithium-containing species on the surface of grains of a layered 4V material such as LiNi1/2Mn1/2O2 along the electrochemical cycling have been followed using 7Li MAS NMR, electrochemical impedance spectroscopy (EIS) and XPS. Materials displaying different specific surface areas and stored in different atmospheres have been investigated in order to study the influence of the surface/volume ratio and the influence of the initial surface state, respectively. It is shown that the presence of an initial interphase of Li2CO3 influences the electrochemical behavior of the electrode, emphasizing the importance of the history of the electrode prior cycling. 7Li MAS NMR experiments performed upon cycling indicate the formation of interphase species in reduction and their partial removal in oxidation, indicating the dynamic character of the interphase upon cycling. Combined NMR, EIS and XPS experiments show the strong influence of the electrode/electrolyte interphase evolution on the electrochemical performance. Such results lead us to draw conclusions on the optimal storage conditions of layered 4V materials for Li-ion batteries such as LiNi1/2Mn1/2O2. [Copyright &y& Elsevier]

Abstract: The changes appearing for LiFePO4–C nano-composites exposed to atmosphere at 120°C have been structurally and chemically examined by the use of TGA, XRD, XPS, Mössbauer, 7Li MAS NMR and electrochemical methods. The results conclude that a highly disordered phase resulting from the aging of LiFePO4 appears on the surface of the grains of the material, is assigned to a phosphate phase and can insert lithium around 2.6V with poor reversibility. The essential role of water has been investigated and clearly demonstrated. Thus, the aging mechanism occurring in hot humid air is completely different from a simple oxidation as well as from the aging process observed above 150°C and involves the incorporation of hydroxyl groups. In addition, Fe2O3 formation has not been observed for such an aging in mild conditions. [ABSTRACT FROM AUTHOR]

Abstract: The evolution of lithium-containing species on the surface of grains of 500nm LiFePO4 and 100nm carbon-coated LiFePO4 materials during the aging process in LiPF6 electrolyte has been followed using coupled 7Li MAS NMR, EIS (Electrochemical Impedance Spectroscopy) and XPS for materials synthesized with and without carbon coating. LiFePO4 undergoes surface reactivity upon immersion in classical LiPF6 electrolyte, although its open circuit voltage (∼3.2V) lies in the thermodynamical stability voltage range. The evolution of the NMR signal shows that the reaction of formation of the interphase is very slow as no evidence of passivation could be found even after 1 month of contact with the electrolyte. 7Li MAS NMR combined with XPS indicates that carbon coating has a strong protective role towards formation of surface species on the material and hinders iron dissolution at elevated temperature. Coupled NMR, EIS and XPS experiments showed that the surface of the material grains is not covered by an homogenous layer. Increasing the storage temperature from 25°C to 55°C promotes the formation of organic species on the surface, most probably covering inorganic species such as LiF, Li x PF y and LiPO y F z . No evidence of the formation of a resistive film is deduced from the evolution of EIS measurements. The interphase growth can accelerate the degradation of the electrochemical performance, leading to a loss of electrical contact within the electrode. [Copyright &y& Elsevier]

Abstract: The impact of air exposure on LiFePO4–C nanocomposites has been investigated at moderate temperature. We show here that the storage in 120°C hot air for 30days leads not only to the material delithiation but also to the formation of an amorphous ferric phosphate side-phase, accounting for 38% of the total iron. The formed phase is found to be partially hydrated, suggesting a water-driven aging mechanism and a proposed hypothetic formula: Li x FePO4(OH) x . The side-phase displays new electrochemical activity but poor cyclability and the overall battery performance is thus deteriorated. The regeneration of pristine structure, together with the performance recovery can be achieved by a simple thermal treatment under inert atmosphere. [Copyright &y& Elsevier]

The evolution of lithium-containing species on the surface of grains of layered LiNi[sub1/2]Mn[sub1/2]O[sub2] material during the aging process in LiPF[sub6] (ethylene carbonate/dimethyl carbonate, I M) electrolyte has been followed using [sup7]Li magic angle spinning NMR spectroscopy. Materials displaying different surface areas have been investigated in order to study the influence of (he surface! volume ratio. The evolution of the NMR signal shows that the reaction of the active material with the electrolyte is extremely fast during the first moments of exposure and tends to slow down for longer exposure times. Coupled NMR, electrochemical impedance spectroscopy, and transmission electron microscopy experiments showed that the surface of the material grains is not covered by a homogeneous layer, indicating that the reaction with electrolyte cannot be considered as a real passivation reaction. The aging process performed on a sample initially stored in ambient atmosphere clearly demonstrates the dissolution of a pristine Li[sub2]CO[sub3] surface layer and the growth of an interphase made primarily of fluorinated compounds. [ABSTRACT FROM AUTHOR]

Abstract: 7Li MAS NMR, usually a bulk characterization technique, is used here to analyze the positive electrode/electrolyte interphase. The sharpening of the NMR spectra line shape as the amount of surface species increases shows that the observed signal is clearly the sum of signals due to the distribution of lithium ions in the interphase in terms of distance from the bulk of electrode active material. This technique is then used to compare characteristics of the interphase coming from the contact with LiPF6-based electrolyte in the case of storage or electrochemical cycling. A clear influence of the change of potential on the interphase configuration and in particular on its intimacy with the bulk of active material is deduced from the change in NMR spectra lineshape. This information is hardly obtained by other characterization technique, making NMR a powerful tool for the study of interphases and passivation layers in lithium batteries materials. [Copyright &y& Elsevier]

The growth and evolution of the interphase, due to contact with the ambient atmosphere or electrolyte, are followed using 7Li magic-angle spinning nuclear magnetic resonance (MAS NMR) in the case of two materials amongst the most promising candidates for positive electrodes for lithium batteries: LiFePO4 and LiMn0.5Ni0.5O2. The use of appropriate experimental conditions to acquire the NMR signal allows observing only the «diamagnetic» lithium species at the surface of the grains of active material. The reaction of LiMn0.5Ni0.5O2 with the ambient atmosphere or LiPF6 (1 M in Ethylene Carbonated/DiMéthyl Carbonate (EC/DMC)) electrolyte is extremely fast and leads to an important amount of lithium-containing diamagnetic species compared to what can be observed in the case of LiFePO4. The two studied materials display a completely different surface chemistry in terms of reactivity and/or kinetics of the surface towards electrolyte. Moreover, these results show that MAS NMR is a very promising tool to monitor phenomena taking place at the interface between electrode and electrolyte. [ABSTRACT FROM AUTHOR]

Keywords: batteries; electrochemistry; energy storage; Mg electrodes; rechargeable Mg batteries EN batteries electrochemistry energy storage Mg electrodes rechargeable Mg batteries 4611 4611 1 11/09/21 20211104 NES 211104 B The Cover Feature b shows the electrochemical performance of 25 m AZ31 alloy as anode, in a full magnesium cell with Chevrel phase as cathode, in 0.25 m APC as electrolyte. Batteries, electrochemistry, energy storage, Mg electrodes, rechargeable Mg batteries. [Extracted from the article]

In order to improve the electrochemical performances of lithium–sulfur batteries, it is crucial to understand profoundly their working mechanism and the limitation factors. This communication presents synchrotron-based in situ XRD studies of structural modifications occurring inside the cell upon cycling, since the active material changes constantly its form between solid and liquid phases. [ABSTRACT FROM AUTHOR]

Ageing of electrolytes used in batteries is a major issue for researchers and industry, as it represents an important cost in the development of new batteries. Past failures to adequately characterize the degradation processes of the electrolyte have led to potentially disastrous safety issues. It is, therefore, paramount to have an in‐depth understanding of the underlying ageing phenomena. On the Inside Back Cover picture, we show that radiolysis techniques can induce similar mechanisms in the electrolyte, allowing for an accelerated assessment of the ageing phenomena within hours. More details can be found in the Full paper by Ortiz et al. on page 3605 in Issue 21, 2015 (DOI: 10.1002/cssc.201500641). [ABSTRACT FROM AUTHOR]

A correction to the article "Electrolytes Ageing in Lithium-ion Batteries: A Mechanistic Study from Picosecond to Long Timescales" that was published in the 2015 issue is presented.

Abstract: Decreasing particle size ensures a good accessibility of LiFePO4 to lithium ions and electrons and allows reaching the theoretical capacity and achieving high cycling rates. It nevertheless leads to an increase of the surface area and thus a subsequent amplification of the parasitic reactions at the interface between active material surface and electrolyte. The formation and evolution of the interphase on the surface of LiFePO4 may affect strongly its electrochemical performance. This work aims at monitoring the interphase forming on LiFePO4 upon its operation in a lithium battery, and correlating its evolution with the electrochemical behaviour of the active material. Combined XPS and multinuclear quantitative 7Li, 1H and 19F NMR indicate a trend for the interphase structure that can be described as a mostly stable inner interphase composed of fluorinated inorganic products while outer lithiated organic species undergo a reversible formation at high potential and dissolution at low potential. Although an irreversible accumulation of interphase occurs, spin–spin relaxation time analysis indicates that interphasial species tend to stack on the top of each other rather than cover the whole active material surface. Moreover, the dissolution/precipitation process seems to prevent a blocking of the electrode surface by resistive species such as LiF. [Copyright &y& Elsevier]

The behavior under irradiation of neat propylene carbonate (PC), a co-solvent usually used in Li-ion batteries (LIB), and also of Li salt solutions is investigated. The decomposition of neat PC is studied using radiolysis in the pulse and steady state regime and is assigned to the ultrafast formation, in the reducing channel, of the radical anion PC − by electron attachment, followed by the ring cleavage, leading to CO. In the oxidative channel, the PC( H) radical is formed, generating CO 2 . The CO 2 and CO yields are both close to the ionization yield of PC. The CO 2 and CO productions in LiClO 4 , LiBF 4 and LiN(CF 3 ) 2 (SO 2 ) 2 solutions are similar as in neat PC. In contrast, in LiPF 6 /PC a strong impact on PC degradation is measured with a doubling of the CO 2 yield due to the high reactivity of the electron towards PF 6 − observed in the picosecond range. A small number of oxide phosphine molecules are detected among the various products of the irradiated solutions, suggesting that most of them, observed in carbonate mixtures used in LIBs, arise from linear rather than from cyclical molecules. The similarity between the degradation by radiolysis or electrolysis highlights the interest of radiolysis as an accelerated aging method. [ABSTRACT FROM AUTHOR]

Abstract: Investigation of electrode/electrolyte interface of 5V spinel material LiNi0.4Mn1.6O4 was carried out in the presence of glutaric anhydride additive, using combined magic angle spinning NMR spectroscopy and electron energy-loss spectroscopy. After exposure to LiPF6 in EC/DMC liquid electrolyte, oxidation state of +III or lower has been evidenced by EELS for Mn ions, indicating that the presence of glutaric anhydride additive in the electrolyte, not only modifies the interphase, but does not prevent chemical reactions with the active material. Further investigation of the influence of the additive upon storage and cycling was performed using combined 7Li and 19F MAS NMR. The native interphase formed by simple contact of the active material with the electrolyte is partially destroyed at high potential but the new appearing interphase is overall increasing upon cycling, independently from the presence of glutaric anhydride. The use of glutaric anhydride is nevertheless beneficial as it clearly restrains the formation of lithiated interphasial species and alters the interphase composition since the formation of fluorophosphates is promoted, lowering the relative amount of resistive LiF. Although resistive LiF can be formed in significant amount, it is removed by the DMC rinsing while fluorophosphates display a stronger adherence to the active material. [Copyright &y& Elsevier]