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Silicon is a very good candidate for the next generation of negative electrodes for Li-ion batteries, due to its high rechargeable capacity. An important issue for the implementation of silicon is the control of the chemical reactivity at the electrode/electrolyte interface upon cycling, especially when using nanometric silicon particles. In this work we observed improved performances of Li//Si cells by using the new salt lithium bis(fluorosulfonyl)imide (LiFSI) with respect to LiPF6. The interfacial chemistry upon long-term cycling was investigated by photoelectron spectroscopy (XPS or PES). A nondestructive depth resolved analysis was carried out by using both soft X-rays (100-800 eV) and hard X-rays (2000-7000 eV) from two different synchrotron facilities and in-house XPS (1486.6 eV). We show that LiFSI allows avoiding the fluorination process of the silicon particles surface upon long-term cycling, which is observed with the common salt LiPF6. As a result the composition in surface silicon phases is modified, and the favorable interactions between the binder and the active material surface are preserved. Moreover a reduction mechanism of the salt LiFSI at the surface of the electrode could be evidenced, and the reactivity of the salt toward reduction was investigated using ab initio calculations. The reduction products deposited at the surface of the electrode act as a passivation layer which prevents further reduction of the salt and preserves the electrochemical performances of the battery. [ABSTRACT FROM AUTHOR]

Recently unveiled 'alkali metal fluorosulphate (AMSOF)' class of compounds offers promising electrochemical and transport properties. Registering conductivity value as high as 10 S cm in NaMSOF phases, we explored the fluorosulphate group to design novel compounds with high Li-ion conductivity suitable for solid electrolyte applications. In the process, we produced sillimanite-structured LiZnSOF by low temperature synthesis ( T ≤ 300 °C). Examining this phase, we accidentally discovered the possibility of improving the ionic conductivity of poor conductors by forming a monolayer of ionic liquid at their particle surface. This phenomenon was studied by solid-state NMR, XPS and AC impedance spectroscopy techniques. Further, similar trends were noticed in other fluorosulphate materials like tavorite LiCoSOF and triplite LiMnSOF. With this study, we propose 'ionic liquid grafting' as an interfacial route to enable good Li-ion conductivity in otherwise poor conducting ceramics. [ABSTRACT FROM AUTHOR]

Mg metal anode‐based battery is a more sustainable, lower cost, and higher energy density alternative to Li‐ion. However, this battery chemistry also faces several challenges associated with the high charge density of Mg2+, including achieving high reversibility and low voltage hysteresis for Mg metal plating/stripping. While significant improvements are achieved in last decades, they involve rather complex electrolyte formulations and/or Mg salts difficult to produce, and the use of unpractical substrates such as platinum. Here, significant improvement in terms of Mg plating kinetics is achieved in electrolytes containing commercial magnesium bis(trifluoromethanesulfonyl)imide salt (Mg(TFSI)2) by using titanium substrate with similar crystal structure and lattice parameter as Mg leading to lower nucleation overpotential. Low salt concentration electrolyte and addition of dibutyl magnesium (Mg(butyl)2) also enable the formation of thinner interphase, richer in solvent based decomposition products, further improving Mg plating kinetics. This work highlights the complex role of Mg(butyl)2, often considered as a simple drying agent, and how it impacts ion solvation favoring the mobility of electroactive cationic species, paving the way toward better electrolyte design with improved cation transference number. [ABSTRACT FROM AUTHOR]

The intricate relationship between local atomic arrangements and electronic states significantly influences the electrochemical properties of Li‐ion battery cathode materials. Despite decades of investigation, a consensus regarding the local atomic and electronic structure of LiNiO2 remains elusive. This ambiguity stems from the potential distortion of Ni sites, either via Jahn‐Teller (JT) distortion or bond disproportionation (BD), complicating the understanding of the charge compensation mechanism involving Ni and O. This study compares the structures of LiNiO2 and NaNiO2, a JT system, using an innovative approach that integrates bulk spectroscopy techniques on standardized interoperable samples for enhanced reliability. While X‐ray absorption spectroscopy and theoretical calculations fail to differentiate between the proposed scenarios, Raman spectroscopy highlights local structural distinctions between monoclinic NaNiO2 and rhombohedral LiNiO2. HAXPES confirms various formal oxidation states for Ni, supported by RIXS data indicating 3d8 states, emphasizing negative charge transfer from Ni and some bond disproportionation in LiNiO2. Regarding charge compensation, XRS and RIXS suggest oxygen hole involvement in redox activity, whereas Raman spectroscopy does not detect molecular oxygen. This comprehensive spectroscopic analysis highlights the importance of correlative characterization workflows in elucidating complex structural‐electrochemical relationships. [ABSTRACT FROM AUTHOR]

Mg fluorinated alkoxyborate-based electrolytes are promising candidates for rechargeable Mg batteries. In this work, we investigate a series of Mg alkoxyborates with a different degree of anion fluorination in terms of their physicochemical properties, Mg metal anode, and organic cathode electrochemical performance, as well as Mg metal/electrolyte interphase. The results underscore the significant influence of the anion fluorination degree on the transport properties of electrolytes. Notably, the anion with the lowest degree of fluorination exhibits one order of magnitude lower ionic conductivity than electrolytes with more fluorinated anions. Interestingly, the same electrolyte demonstrates the second-best electrochemical performance, with the Mg plating/stripping efficiency close to 99 %. XPS analysis of the Mg metal deposit surface reveals that the high Coulombic efficiency is associated with a high amount of boron-containing species in the metal/electrolyte interphase of the best-performing electrolytes. Additionally, it has been noted that inorganic boron species result in a larger interfacial resistivity for Mg plating/stripping compared to boron species in an organic environment. Testing in combination with organic cathodes reveals the superior performance of the most fluorinated electrolyte in terms of cycling stability and Coulombic efficiency. The present work underlines the interplay of different phenomena affecting the overall electrochemical performance of electrolytes and strategies for the design of next-generation Mg electrolytes. [Display omitted] • Investigation of the ligand fluorination degree on the performance of Mg alkoxyborate electrolytes. • Low ionic conductivity and limited dissociation of the electrolyte with least fluorinated ligand. • Mg plating/stripping efficiency close to 99 % for two best performing electrolytes. • Beneficial effect of higher amount of boron species in the Mg metal/electrolyte interphase. • Best organic cathode cycling performance with most fluorinated alkoxyborate electrolyte. [ABSTRACT FROM AUTHOR]

The demonstration of reversible anionic redox in Li-rich layered oxides has revitalized the search for higher energy battery cathodes. To advance the fundamentals of this promising mechanism, we investigate herein the cationic-anionic redox processes in Li2Ru0.75Sn0.25O3—a model Li-rich layered cathode in which Ru (cationic) and O (anionic) are the only redox-active sites. We reveal its charge compensation mechanism and local structural evolutions by applying operando (and complementary ex situ) X-ray absorption spectroscopy (XAS). Among other local effects, the anionic-oxidation-driven distortion of the oxygen network around Ru atoms is thereby visualized. Oxidation of lattice oxygen is also directly proven via hard X-ray photoelectron spectroscopy (HAXPES). Furthermore, we demonstrate a spectroscopy-driven visualization of electrochemical reaction paths, which enabled us to neatly decouple the individual cationic-anionic dQ/dV contributions during cycling. We hence establish the redox and structural origins of all dQ/dV features and demonstrate the vital role of anionic redox in hysteresis and kinetics. These fundamental insights about Li-rich systems are crucial for improving the existing anionic-redox-based cathodes and evaluating the ones being discovered rapidly. [ABSTRACT FROM AUTHOR]

Argyrodite Li6PS5Cl is a good candidate for being a solid electrolyte for bulk all-solid-state Li-ion batteries because of its high ionic conductivity and its good processability. However, the interface stability of sulfide-based electrolytes toward active materials (negative or positive electrodes) is known to be lower than that of oxide-based electrolytes. In this work, we investigate the interface stability of argyrodite toward several positive electrode materials: LiCoO2, LiNi1/3Co1/3Mn1/3O2, and LiMn2O4. All-solid-state half-cells were cycled, and the interface mechanisms were characterized by Auger electron spectroscopy and X-ray photoelectron spectroscopy. We show that Li6PS5Cl is oxidized into elemental sulfur, lithium polysulfides, P2Sx (x ≥ 5), phosphates, and LiCl at the interface with the positive electrode active materials. In spite of this interface reactivity, good capacity retention was observed over 300 cycles. Li6PS5Cl shows some reversible electrochemical activity (redox processes) that might contribute to the reversible capacity of the battery. [ABSTRACT FROM AUTHOR]

Argyrodite Li 6 PS 5 Cl is a good candidate as solid electrolyte for bulk all-solid-state Li-ion batteries due to its high ionic conductivity and its good processability, although it shows some interface reactivity towards electrode active materials. In this work we have cycled LiCoO 2 /Li 6 PS 5 Cl/Li 4 Ti 5 O 12 full cells and analyzed the interfacial mechanisms by surface-sensitive characterization techniques: Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS). We show that Li 6 PS 5 Cl has an electrochemical redox activity in the positive electrode. It is partially oxidized into LiCl, P 2 S 5 and polysulfides Li 2 S n upon charge, with some reversibility upon discharge. Li 6 PS 5 Cl also reacts with LiCoO 2 upon cycling, leading to the formation of phosphates at the interface. [ABSTRACT FROM AUTHOR]

In this paper, we report positive effect of Tris(2,2,2-trifluoroethyl) phosphite (TTFP) as additive during initial activation and cycling of Li-rich-NMC x Li 2 MnO 3 –(1 − x )LiMO 2 ( x >> 1; M = Ni, Co, Mn) cathode in EC/DMC + 1 M LiPF 6 electrolyte. Firstly conductivity and viscosity of electrolyte with x wt.% TTFP; 0 wt.% < x < 20 wt.% were studied. From the electrochemical characterization using cyclic voltammetry, galvanostatic charge/discharge and EIS we show that TTFP passives aluminum current collector and the acts as oxygen scavenger during the extended activation plateau up 4.7 V vs . Li + /Li (up to 301 mAh g −1 in charge). The beneficial effect of TTFP improves the long-term cycling stability of the cathode with more than 95% of initial capacity in Gr//Li-Rich -NMC full cell is maintained after 50 cycles at C rate. Finally, XPS analysis of Li-rich -NMC electrodes show presence of TTFP on the surface during cycling and confirm the presence of Mn 3+ at the end of discharge. The convergence of all characterizations indicates that TTFP should act as a catalyst to several surface reactions which are beneficial to long cycling cell performances. [ABSTRACT FROM AUTHOR]

Discharge/charge process of classical lithium sulphur battery proceeds through intermediate polysulphides which are soluble in classical electrolyte systems. Due to concentration gradient soluble polysulphides easily diffuse/migrate out from cathode composite forming non-uniform distribution of the sulphur within cathode. Eventually polysulphides can be completely reduced on the metallic lithium anode. In this work we compare the sorption properties of manganese modified zeolite silicalite-1 (MnS-1) with a cathode composite containing SBA-15 additive and a cathode composite without additive. Careful analysis using XPS and FIB microscopy equipped with EDX show improved retention of polysulphide species within cathode composite in the case of MnS-1 zeolite as an additive. Interestingly, the amount of sulphur species detected by XPS on the metallic lithium is very similar regardless on cathode composite we use. Finally, similar cycling behaviour can be observed if MnS-1 zeolite is used as an interlayer between composite cathode and separator. [ABSTRACT FROM AUTHOR]

Abstract: A synthesis method consisting of a mechanical ball milling activation process followed by a sintering heating treatment is proposed to obtain MnSn2 as anode material for Li-ion batteries. This two-step approach strongly reduces the amount of βSn impurities and provides a better material morphology. This improves the electrochemical performances, even at high C-rate, as shown from the comparison between electrode materials obtained with and without this preliminary activation process. The electrochemical reactions have been followed at the atomic scale by in situ 119Sn Mössbauer spectroscopy. The first discharge is a restructuring step that transforms the pristine material into Mn/Li7Sn2 nanocomposite which should be considered as the real starting material for cycling. The delithiation of this nanocomposite is characterized by two plateaus of potential attributed to the de-alloying of Li7Sn2 followed by the back reaction of Mn with poorly lithiated Li x Sn alloys, respectively. The composition and the stability of the solid electrolyte interphase were characterized by X-ray photoelectron spectroscopy. [Copyright &y& Elsevier]

Abstract: Li(Ni,Mn,Co)O2/carbon lithium-ion batteries designed to work at high temperature exhibit good performances for cycling at 85 °C but a strong impedance increase for cycling or storage at 120 °C. The effects of high temperature on the aging process of positive electrode''s binder, electrodes/electrolyte interfaces and positive active material were investigated by bulk and surface analysis techniques: X-ray diffraction, 7Li and 19F Nuclear Magnetic Resonance, Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy. The main phenomenon observed at 120 °C is a migration of PVdF binder from the outer part of the positive electrode which thus shows a bad Li reintercalation. Binder migration results in the formation of a PVdF layer at the extreme surface of the positive electrode, and in its diffusion and deposition on the surface of the negative electrode. Several changes in the composition of the Solid Electrolyte Interphase (SEI) were also evidenced between a cycle at 60 °C and cycling at 85 °C and 120 °C. Disappearance of carbonate species disappearance and increase of inorganic species, which both together may also affect battery''s performance. Though, since the battery can undergo 25 cycles at 120 °C, Li(Ni,Mn,Co)O2 seems to be an appropriate material for high temperature cycling. [Copyright &y& Elsevier]

Abstract: The performances and mechanisms of two types of anodes formed by FeSn2 microparticles and nanostructured FeSn2, respectively, were studied by Mössbauer spectroscopy and electrochemical testing. The specific capacity, which is within the range 400–600mAhg−1 even at high C-rate, did not vary with cycle number over 50–60 cycles for the microparticles but progressively decreased for the nanostructured material. In the two cases, the first discharge consists in the irreversible transformation of FeSn2 into Fe/Li7Sn2 nanocomposite. The capacity fade is attributed to the growth and/or coalescence of the particles during cycling. [Copyright &y& Elsevier]

The revival of the Na‐ion battery concept has prompted intense research activities toward new sustainable Na‐based insertion compounds and their implementation in full Na‐ion cells. Efforts are parted between Na‐based polyanionic and layered compounds. For the latter, there has been a specific focus on Na‐deficient layered phases that show cationic and anionic redox activity similar to a Na0.67Mn0.72Mg0.28O2 phase. Herein, a new alkali‐deficient P2‐Na2/3Mn7/9Zn2/9O2 phase using a more electronegative element (Zn) than Mg is reported. Like its Mg counterpart, this phase shows anionic redox activity and no O2 release despite evidence of cationic migration. Density functional theory (DFT) calculations show that it is the presence of an oxygen nonbonding state that triggers the anionic redox activity in this material. The phase delivers a reversible capacity of 200 mAh g−1 in Na‐half cells with such a value be reduced to 140 mAh g−1 in full Na‐ion cells which additionally shows capacity decay upon cycling. These findings establish Na‐deficient layered oxides as a promising platform to further explore the underlying science behind O2 release in insertion compounds based on anionic redox activity. The doping of layered sodium based oxide with Zn electronegative d10 ions allows adaptation of energy bands to create nonbonding O(2p) states that can be activated. Characterization carried out ex situ and in operando shows that P2‐Na2/3[Mn7/9Zn2/9]O2 demonstrates reversible cumulative cationic and anionic redox activity while, despite no O2 release, a migration of cations occurs progressively. [ABSTRACT FROM AUTHOR]