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Ni-rich layered oxides, in a general term of Li(Ni

Replacement of graphite with alloying and conversion materials, having high specific capacity, has emerged as versatile route to increasing the energy density of Li-ion batteries. A key challenge is the large volume change in these materials, which leads to an unstable solid electrolyte interphase (SEI). The use sacrificial electrolyte additives, such as fluoroethylene-carbonate (FEC), has been established as an effective strategy for considerably improving cycling stability, but a mechanistic understanding of the underlying processes has been lacking so far. Here, we present an in-depth chemical and morphological study of the FEC-based interphase on graphite and SnO2–graphite model electrodes. We found that the FEC decomposition products aggregate first into spherical particles, whose growth depends on the cell medium and follows the laws of crystal-growth theory, before forming a continuous carbonate-rich film. The discrimination of the chemical composition of the FEC-derived particles from the rest of the electrode was obtained by X-ray photoemission electron microscopy (XPEEM) due to the high lateral resolution of this technique. The obtained understanding of SEI formation in fluorine-rich electrolytes should help to guide future designs of sacrificial fluorine-based additives.

The growth of crystalline Li-based oxide thin films on silicon substrates is essential for the integration of next-generation solid-state lithionic and electronic devices including on-chip microbatteries, memristors, and sensors. However, growing crystalline oxides directly on silicon typically requires high temperatures and oxygen partial pressures, which leads to the formation of undesired chemical species at the interface compromising the crystal quality of the films. In this work, we employ a 2 nm gamma-alumina (γ-Al

All-solid-state lithium batteries are a promising alternative for next-generation safe energy storage devices, provided that parasitic side reactions and the resulting hindrances in ionic transport at the electrolyte-electrode interface can be overcome. Motivated by the need for a fundamental understanding of such an interface, we present here real-time measurements of the (electro-)chemical reactivity and local surface potential at the electrified interface (Li2S)3-P2S5 (LPS) and LiCoO2 (LCO) using operando X-ray photoelectron spectroscopy (XPS) supplemented by X-ray photoemission electron microscopy (XPEEM). We identify three main degradation mechanisms: (i) reactivity at open circuit potential leading to the formation of reduced Co in the +2 oxidation state at the LCO surface, detected in the Co L-edge, which is further increased upon cycling, (ii) onset of electrochemical oxidation of the LPS at 2.3 V vs InLix detected in the S 2p and P 2p core levels, and (iii) Co-ion diffusion into the LPS forming CoSx species at 3.3 V observed in both S 2p and Co 2p core levels. Concurrently, a local surface overpotential of 0.9 V caused by a negative localized charge layer is detected at the LPS-LCO interface. Furthermore, in agreement with previous theoretical results, the presence of a sharp potential drop at the interface between active materials and solid electrolyte is demonstrated in all-solid-state batteries.

The advancement of liquid electrolytes in Li-metal batteries is an important strategy to realize a robust and uniform solid electrolyte interphase (SEI) on the Li metal anode while simultaneously achieving high oxidative stability and addressing the shortcomings of traditional carbonate and ether-based electrolytes suffering from side reactions and high-voltage decomposition, respectively. To circumvent these challenges, here, a fluorinated dioxolane-based cyclic co-solvent, that is 2-(2,2,2-trifluoroethoxy)-4-(trifluoromethyl)-1,3-dioxolane (TTD), is developed. After pairing 1.5 M lithium bis(fluorosulfonyl)imide (LiFSI) with TTD and 1,2-dimethoxyethane (DME), the 1.5 M LiFSI-8TTD-2DME electrolyte exhibits remarkable oxidation stability up to 6 V and a Coulombic efficiency of 99.4% over 210 cycles at 3 mA cm–2with a cut-off capacity of 3 mA h cm–2in the Li|Cu half-cell originating from efficient regulation of the electrolyte solvation structure and consequent anion-derived inorganic SEI layer formation. Full cells with advanced electrolytes, using 20 μm of Li foil paired with the NCM811 cathode by a negative and positive capacity ratio (N/P) of 2.5, achieve 75% capacity retention after 160 cycles at 0.5 C. Furthermore, even at an ultra-high charge cut-off voltage of 4.7 V, the Li|NCM811 full cell still realizes 80% retention at 0.5 C after 100 cycles.

We experimentally determine the redox reactions during (de-)lithiation of the SnO2 working electrode cycled in (Li2S)3-P2S5 solid electrolyte by combining operando X-ray photoelectron spectroscopy and in situ X-ray absorption spectroscopy. Specifically, we have accurately determined the composition changes in the SnO2 working electrode upon cycling and identified the onset voltage formation of the various phases. Starting from the open-circuit potential, we find that, on lithiation, the Sn M-edge absorption spectra reveal unequivocally the formation of SnOx (x ≤ 1) and Li2SnO3 already at a potential of 1.6 V vs Li+/Li, while Sn 3d/Sn 4d, O 1s, and Li 1s core-level spectra show the formation of Sn0 and Li2O along the first potential plateau at 0.8 V vs Li+/Li and of Li8SnO6 at lower potentials. Below 0.6 V vs Li+/Li, an alloying reaction takes place until the end of the lithiation process at 0.05 V vs Li+/Li, as shown by the formation of LixSn. During delithiation, both the conversion and alloying reactions are found to be partially reversible, starting by the re-formation of Sn0 at 0.3 V vs Li+/Li and followed by the re-formation of Li8SnO6 and SnOx above 0.5 V vs Li+/Li. The conversion and alloying reactions are found to overlap during both lithiation and delithiation. Finally, we validate the theoretical prediction for the SnO2 conversion and alloy (de-)lithiation reactions and clarify the open questions about their reaction mechanism.

Improving the interfacial stability between the electrode and the electrolyte at high voltage is a key to successfully obtain high energy-density Li-ion batteries. Therefore, this study is dedicated to a novel multifunctional electrolyte additive, methoxytriethyleneoxypropyltrimethoxysilane (MTE-TMS), able to stabilize the interface of both Ni-rich layered LiNi0.85Co0.1Mn0.05O2 (NCM851005) cathode and graphite anode in a full-cell. Electrochemical tests reveal that the addition of 1 wt% MTE-TMS significantly improves the long-term cycling stability of the graphite‖NCM851005 full-cell, with an achieved maximum capacity of 198 mAh g−1 and its excellent capacity retention of 84% after 100 cycles at C/5 using upper voltage cut-off of 4.3 V vs Li+/Li. In contrast, the standard electrolyte in absence of MTE-TMS leads to a rapid performance fade. The significantly improved electrochemical performance is attributed to the formation of a stable surface protective film at both the cathode and the anode surfaces upon long-term cycling in elevated voltage window, and thus suppressing the electrolyte decomposition at and structural degradation of both cathode and anode, resulting as well in reduced transition metal transfer between the two electrodes.

Ether-based electrolytes offer promising features such as high lithium-ion solvation power and stable interface, yet their limited oxidation stability impedes application in high-voltage Li-metal batteries (LMBs). Whereas the fluorination of the ether backbone improves the oxidative stability, the resulting solvents lose their Li+-solvation ability. Therefore, the rational molecular design of solvents is essential to combine high redox stability with good ionic conductivity. Here, we report the synthesis of a new high-voltage fluorinated ether solvent through integrated ring-chain molecular design, which can be used as a single solvent while retaining high-voltage stability. The controlled Li+-solvation environment even at low-salt-concentration (1 M or 2 M) enables a uniform and compact Li anode and an outstanding cycling stability in the Li|NCM811 full cell (20 μm Li foil, N/P ratio of 4). These results show the impact of molecular design of electrolytes towards the utilization of LMBs.

All-solid-state lithium batteries are a promising alternative for next-generation safe energy storage devices, provided that parasitic side reactions and the resulting hindrances in ionic transport at the electrolyte-electrode interface can be overcome. Motivated by the need for a fundamental understanding of such an interface, we present here real-time measurements of the (electro-)chemical reactivity and local surface potential at the electrified interface (Li

X-ray photoemission electron microscopy (XPEEM), with its excellent spatial resolution, is a well-suited technique for elucidating the complex electrode-electrolyte interface reactions in Li-ion batteries. It provides element-specific contrast images that allows the study of the surface morphology and the identification of the various components of the composite electrode. It also enables the acquisition of local X-ray absorption spectra (XAS) on single particles of the electrode, such as the C and O K-edges to track the stability of carbonate-based electrolytes, F K-edge to study the electrolyte salt and binder stability, and the transition metal L-edges to gain insights into the oxidation/reduction processes of positive and negative active materials. Here we discuss the optimal measurement conditions for XPEEM studies of Li-ion battery systems, including (i) electrode preparation through mechanical pressing to reduce surface roughness for improved spatial resolution; (ii) corrections of the XAS spectra at the C K-edge to remove the carbon signal contribution originating from the X-ray optics; and (iii) procedures for minimizing the effect of beam damage. Examples from our recent work are provided to demonstrate the strength of XPEEM to solve challenging interface reaction mechanisms via post mortem measurements. Finally, we present a first XPEEM cell dedicated to operando/in situ experiments in all-solid-state batteries. Representative measurements were carried out on a graphite electrode cycled with LiI-incorporated sulfide-based electrolyte. This measurement demonstrates the strong competitive reactions between the lithiated graphite surface and the Li2O formation caused by the reaction of the intercalated lithium with the residual oxygen in the vacuum chamber. Moreover, we show the versatility of the operando XPEEM cell to investigate other active materials, for example, Li4Ti5O12.

The (electro-)chemical reactivity and electronic properties across electrified solid–solid interfaces critically determine the functionality of solid-state electrochemical devices. To date, questions still arise in the scientific community due to the limitations of surface-sensitive characterization techniques, especially in post-mortem mode. Particularly, parameters such as the electrochemical stability of the solid electrolyte (SE) as well as the ionic and electronic percolation within the composite electrode are essential in order to push all-solid-state lithium-ion batteries (SSBs) towards practical applications. In this work, we highlight operando X-ray photoelectron spectroscopy (XPS) as a straightforward method to monitor the SE reduction within a composite electrode consisting of Li4Ti5O12 (LTO) as the electrode active material, (Li2S)3–P2S5 (LPS) as the SE and vapor-grown carbon fiber as the conductive additive under real working conditions. The results clarify previous discrepancies between experimental and theoretical results regarding the anodic stability limit of LPS and also reveal the limitations of post-mortem XPS measurements that can potentially lead to misinterpretations. We identify the reduction process of LPS which starts at 1.7 V vs. Li+/Li (1.1 V vs. InLix), resolved as a two-step process accompanied by the formation of electronically insulating Li2S and electronically conductive LixP species. Furthermore, the operando methodology resolves the LTO redox activity and the distribution of conductive and non-conductive LTO species as a function of their lithiation states. This allows a deeper understanding of both the lithium-ion transport through the composite electrode and the characteristic metal–insulator transition associated with LTO. Finally, we discuss how the interfacial reactivity between LPS and LTO impacts the electrochemical performance of SSBs.

The encouraging selectivity of copper oxides for the electroreduction of CO2 into ethylene and alcohols has led to a vivid debate on the possible relation between their operando (sub-)surface oxidation state (i. e. fully reduced or partially oxidized) and this distinct reactivity. The high roughness of the Cu oxides used in previous studies on this matter adds complexity to this controversy and motivated us to prepare quasi-planar Cu2 O thin films that displayed a CO2 reduction selectivity similar to that of oxide-derived copper catalysts reported in previous studies. Most importantly, when the post-mortem thin films were transferred for characterization in an air-free environment, X-ray photoelectron spectroscopy measurements confirmed their complete reduction in the course of the CO2 reduction reaction. Thus, our results indicate that the selectivity of the Cu oxides featured in previous studies stems from their enhanced roughness, highlighting the importance of controlled sample transfer upon post-mortem characterization with ex situ techniques.

Control of electrode-electrolyte interfacial reactivity at high-voltage is a key to successfully obtain high-energy-density lithium-ion batteries. In this study, 2-aminoethyldiphenyl borate (AEDB) is investigated as a multifunctional electrolyte additive in stabilizing surface and bulk of both Ni-rich LiNi0.85 Co0.1 Mn0.05 O2 (NCM851005) and graphite electrodes in a cell operated with elevated upper cutoff voltage of 4.4 V vs. Li+ /Li. The presence of AEDB in a full-cell inhibits structural degradation of both cathode and anode materials, suppressing crack formation, and reduces metal dissolution at the cathode and metal deposition at the anode. As a consequence, the interfacial resistance is significantly reduced. Moreover, this is a case where "the whole is greater than the sum of the parts": the effect of AEDB in half-cells is rather modest, whereas in full-cells its addition results in tremendous performance improvement. The graphite‖NCM851005 full-cell in the presence of AEDB has a capacity retention of 88 % after 100 cycles, even when the upper cutoff voltage is set to 4.35 V, corresponding to 4.4 V vs Li+ /Li, whereas with standard electrolyte under the same conditions it is only 21 %. The study shows a simple and easy approach to using Ni-rich cathodes in an extended voltage window and demonstrates the importance of full-cell testing for electrolyte additive selection.

The lithium (Li) metal anode is considered to be a promising candidate for next-generation batteries but is impeded by Li dendrites and the resulting poor reversibility. Here, we introduce monoquat salts with an ability to anchor onto the Li metal surface through pyridine moieties as electrolyte additives. We systematically varied both the number and the spatial arrangement of anchoring units along with the number of positive charges bearing PF6counteranions to probe their impact on Li metal protection. A high surface concentration of PF6counteranions and their immediate reaction with the deposited Li facilitate the in situ formation and homogeneous distribution of LiF in the surface passivation layer. Our results revealed that the monoquat dication, through stable pyridine-based anchoring, formed an ionically conductive and dense solid electrolyte interphase layer and showed superior cycling performance in both ether-based and carbonate-based electrolytes, thus clearly demonstrating the importance of the anchoring strategy for Li metal surface protection.

We report the excellent cycling stability of graphite in combination with two types of sulfide solid electrolytes, 0.75Li2S-0.25P2S5 (LPS) and 0.3LiI-0.7(0.75Li2S-0.25P2S5), and discuss the stability of the graphite-solid electrolyte interface by analyzing the normalized cumulative irreversible charge and the total amount of lithium consumed at the lithiated state. The rate limitations and the influence of the morphology and the size of graphite particles on the utilization of the electrode are studied as well. At higher current densities, the utilization of the graphite is decreasing as a consequence of the poor effective ionic conductivity of the composite electrode, which is also evidenced by the increasing polarization and ohmic resistance across the electrode.

The surface evolution of LiNi

This chapter focuses on the ability of X-ray photoemission electron microscopy (XPEEM) to provide local spectroscopic information and therefore of probing the electronic structure of materials down to the nm scale. It provides a brief description of the working principles of XPEEM and illustrates with examples from the literature the gamut of possibilities for studying materials systems in areas ranging from physics, chemistry, biology, and materials science, with an emphasis on local, nanoscale spectromicroscopy. XPEEM relies on the imaging of electrons emitted from the sample upon excitation with X-rays. Composite structures correspond to bulk materials made of two or more components that interact in such a way as to yield properties that differ from the isolated parts. The high lateral spatial resolution of XPEEM is particularly well suited for the investigation of nanodevices or their building blocks, which might be composed of semiconducting, metallic, or oxide materials.

For Li-ion batteries, the Li-ion solvation in liquid electrolytes is a crucial parameter affecting directly the electrochemical cycling performance. X-ray photoelectron spectroscopy (XPS) can play an essential role for investigating the cation and anion electronic structure and monitoring the Li-ion solvation into various solvent and salt environments. In this contribution, we demonstrate the capability of conventional laboratory XPS using Al Kα X-ray source to determine the anions solvation shell of Li+ cation within the low vapour pressure and vacuum compatible ionic liquid electrolytes. 1M of LiTFSI and 1M of LiFSI salts dissolved in (EMIM+-FSI-) and (EMIM+-TFSI-) ionic liquids respectively are investigated by acquiring the F1s, N1s, C1s, S2p and Li1s core levels. The binding energy difference between the N1s component originating from the EMIM+ cation and the N1s component originating from TFSI- or FSIanions solvating the Li+ confirms that both TFSI- and FSIcontribute simultaneously to the Li+ solvation. Additionally, the stability of the TFSI and FSI -based ionic liquid electrolytes is carefully discussed for long X-ray exposure times.

International audience; SnO2 is an attractive negative electrode for Li-ion battery owing to its high specific charge compared to commercial graphite. However, the various intermediate conversion and alloy reactions taking place during lithiation/delithiation, as well as the electrolyte stability, have not been fully elucidated, and many ambiguities remain. An amorphous SnO2 thin film was investigated for use as a model electrode by a combination of postmortem X-ray photoelectron spectroscopy supported by density functional theory calculations and scanning electron microscopy to shed light on these different processes. The early stages of lithiation reveal the presence of multiple overlapping reactions leading to the formation of Li2SnO3 and Sn0 phases between 2 and 0.8 V vs Li+/Li. Between 0.45 V and 5 mV vs Li+/Li Li8SnO6, Li2O and LixSn phases are formed. Electrolyte reduction occurs simultaneously in two steps, at 1.4 and 1 V vs Li+/Li, corresponding to the decomposition of the LiPF6 salt and ethylene carbonate/dimethyl carbonate solvents, respectively. Most of the reactions during delithiation are reversible up to 1.5 V vs Li+/Li, with the reappearance of Sn0 accompanied by the decomposition of Li2O. Above 1.5 V vs Li+/Li, Sn0 is partially reoxidized to SnOx. This process tends to limit the conversion reactions in favor of the alloy reaction, as also confirmed by the long-term cycling samples.

Targeting the long-term performance retention of high-energy-density batteries, a facile yet effective surface coating approach for high-voltage composite cathodes was developed. Ultra-thin polyacrylate (PAA) surface coatings with an estimated thickness of less than 5 nm were integrated onto Li-rich Li(NixCoyMnz)O2 cathodes through a solution-casting method. Obvious improvements of specific charge – around 20 mA h g−1 at the 1st cycle and up to 50 mA h g−1 at the 100th cycle – as well as enhanced capacity retention were achieved post the integration of a lithium polyacrylate (LiPAA) surface coating. A fundamental understanding of the role of PAA coatings was systematically achieved by X-ray photoelectron spectroscopy (XPS), electron microscopy (TEM, SEM/EDX), Fourier transform infrared spectroscopy (FTIR) and online electrochemical mass spectrometry (OEMS). Physically adhesive coatings on the active sites of cathodes were observed, which might contribute to impeded surface reconstruction of active materials during cycling. Furthermore, in OEMS analysis reduced CO2 evolution was detected from coated electrodes, indicating that the LiPAA coating could interrupt electrolyte decomposition reactions and enhance the cathode/electrolyte interfacial stability at high anodic potentials. This functional polymer coating acts as a stable artificial polymeric interphase to mitigate electrode and electrolyte decomposition during long-term cycling.

The safe operation and long life-span of Li-ion batteries rely on a stable electrode–electrolyte interface. However, determining the thermodynamic stability window of such an interface is challenging due to the different (electro)chemical reactivities of the electrode components. Here we demonstrate a holistic experimental and theoretical approach to elucidate the nature and origin of the multiple reactions at such complex interfaces, which remain a major obstacle for the development of next generation Li-ion batteries. We applied X-ray photoemission electron microscopy (XPEEM) on Li4Ti5O12 electrodes to solve, with nanoscale resolution, its controversial surface reactivity in carbonate-based electrolytes. Local X-ray absorption spectroscopy (XAS) is performed upon cycling on individual carbon and Li4Ti5O12 particles, while maintaining their working environment, as in the commercial-like electrode composition. Despite the theoretical prediction of a stable electrochemical interface, we find that electrolyte reduction occurs solely on Li4Ti5O12 particles during lithiation at 1.55 V vs. Li+/Li. With the support of density functional theory (DFT) calculations, we show that this behavior is caused by the solvents adsorbed on the Li4Ti5O12 outer planes driven by the Li-ion insertion. The DFT results indicate that Li-ion insertion leads to a shift of the LUMO of the adsorbed solvents to energies below the Fermi level position of lithiated Li7Ti5O12 and thus to chemical instability. Simultaneously, at the same potential, we detect a competing reaction that leads to the partial dissolution of the electrolyte by-product layer. Such a finding has to be considered for other insertion materials and needs to be addressed in surface engineering to mitigate side reactions and design safe and long-lasting batteries.

Understanding the degradation of the solid electrolyte-electrodes interface during cycling is currently one of the most challenging obstacles in the development of all-solid-state batteries. Here, we introduce operando X-ray photoelectron spectroscopy (XPS) as a combined approach for real-time monitoring of the (i) (electro-) chemical interfacial reactions between different components of the composites electrode and (ii) surface electronic properties. The dedicated electrochemical cell, capable of maintaining high mechanical pressure, offers reliable electrochemistry and versatility in terms of materials application. We propose a fundamental physical model to explain the effect of applied cell voltage on core level binding energy shifts, which allows direct contactless measurement of the surface potentials. Such a fundamental understanding is also an essential prerequisite for (i) accurate interpretation of the XPS core level peaks, (ii) the assignment of solid electrolyte decomposition byproducts and (iii) an improved description of the interfacial reaction mechanisms in all-solid-state batteries. A mixture of LiCoO2 (LCO) and (Li2S)3-P2S5 (LPS) cycled vs. InLix is investigated revealing that the LPS oxidation begins above 2.1 V vs. InLix and the byproducts passivate the composite surface against further oxidation. Moreover, we confirm that LCO particles are electronically conductive even in the absence of conductive additives by measuring directly its surface potential during cycling.

International audience; All-solid-state lithium-ion batteries represent a promising battery technology thanks to the replacement of the volatile and flammable state-of-the-art liquid electrolyte by a solid electrolyte. Despite the recent progress in the synthesis of sulfide based solid electrolyte with high ionic conductivity, little is known about the interface reactivity of the solid electrolyte with electrode materials. In this study, we synthesized and characterized an amorphous solid electrolyte with the nominal composition (Li2S)3(P2S5). We assessed the feasibility of using this electrolyte at the laboratory scale, and we discuss the potential challenges that govern its electrochemical performance. Galvanostatic cycling and rate performance measurements were conducted using lithium titanium oxide (Li4Ti5O12) as the negative electrode material. The electrochemical measurements were performed using two different counter electrodes, namely Li metal and an InLix alloy. The alloy counter electrode suppressed the formation of lithium dendrites, resulting in increased cycling stability and cell safety. Post mortem X-ray photoemission spectroscopy measurements reveal the reactivity of the solid electrolyte Li3PS4 with the Li4Ti5O12, lithium metal, and InLix alloy.

We study the oxo-hexametallate Li$_7$TaO$_6$ with first-principles and classical molecular dynamics simulations, obtaining a low activation barrier for diffusion of $\sim$0.29 eV and a high ionic conductivity of $5.7 \times 10^{-4}$ S cm$^{-1}$ at room temperature (300 K). We find evidence for a wide electrochemical stability window from both calculations and experiments, suggesting its viable use as a solid-state electrolyte in next-generation solid-state Li-ion batteries. To assess its applicability in an electrochemical energy storage system, we performed electrochemical impedance spectroscopy measurements on multicrystalline pellets, finding substantial ionic conductivity, if below the values predicted from simulation. We further elucidate the relationship between synthesis conditions and the observed ionic conductivity using X-ray diffraction, inductively coupled plasma optical emission spectrometry, and X-ray photoelectron spectroscopy, and study the effects of Zr and Mo doping.

The encouraging selectivity of copper oxides for the electroreduction of CO

This paper provides valuable insights into the kinetics of the vanadium (V) reduction reaction occurring at a glassy carbon (GC) model electrode surface treated by different oxidative and mechanical methods. Oxidative treatments were applied by thermal, acid and electrochemical means. Mechanical polishing on an abrasive sandpaper surface was used to prepare a rough GC electrode, this surface was also further electrochemically oxidised. The resulting surfaces were studied by x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Activity is defined in terms of peak potential separation (ΔEp) and this descriptor was verified by EIS. No correlation between activity and oxygen to carbon ratio (O/C) or any specific oxygen functional group was found in this study. Raman spectroscopy revealed significant structural changes for GC electrodes treated by electrochemical oxidation and abrasive polishing. A correlation between structural disorder in GC and improvements in activity was observed. However, a limit of structural disorder exists, beyond which no substantial improvements in activity can be achieved.

Partial lithium substitution with nickel (0.25 of Ni2+ ion) in the previously reported Li1.5Fe0.5Ti1.5(PO4)3/C (LFTP@C) was performed to improve its structural and electrochemical properties. The new LiNi0.25Fe0.5Ti1.5(PO4)3/C (LNFTP@C) material was then tested as electrode for lithium ion batteries. In the voltage window 1.85V–3.0 V vs. Li+/Li, attractive electrochemical performances were obtained, mostly in terms of rate capability performance. At a current rate of 0.1C (6.6 mAg−1), the material delivered a capacity of around 120 mAhg−1, while at 5C, we observed a slight drop of the specific capacity reaching a value of 108 mAhg−1. Long-term cycling performance stability was also tested demonstrating a remarkable capacity decrease during the last 500 cycles. The capacity retention decreased from 94% to 91% after 500 cycles to about 77% and 74% after 1000 cycles at fast current rates of 5C (329.8 mAg−1) and 10C (659.6 mAg−1), respectively. In the wider voltage window, an average specific capacity of around 380 mAhg−1 was attained at a slow current rate of 0.1C.

The surface evolution of LiNi0.8Co0.15Al0.05O2 (NCA) and Li4Ti5O12 (LTO) electrodes cycled in a carbonate-based electrolyte was systematically investigated using the high lateral resolution and surface sensitivity of x-ray photoemission electron microscopy combined with x-ray absorption spectroscopy and x-ray photoelectron spectroscopy. On the cathode, we attest that the surface of the pristine particles is composed of adventitious Li2CO3 together with reduced Ni and Co in a +2 oxidation state, which is directly responsible for the overpotential observed during the first de-lithiation. This layer decomposes at 3.8 V vs Li+/Li, leaving behind a fresh surface with Ni and Co in a +3 oxidation state. The charge compensation upon Li+ extraction takes place above 4.0 V and is assigned to the oxidation of both Ni and oxygen, while Co remains in a +3 oxidation state during the whole redox process. We also identified the formation of an inactive surface layer already at 4.3 V, rich in reduced Ni and depleted in oxygen. However, at 4.9 V, NiO-like species are detected accompanied with reduced Co. Despite the highly oxidative potential, the surface of the cathode after long cycling is free of oxidized solvent byproducts but contains traces of LiPF6 byproducts (LiF and POxFy). On the LTO counter electrode, transition metals are detected only after long cycling vs NCA to 4.9 V as well as PVdF and LiPF6 byproducts originating from the cathode. Finally, harvested cycled electrodes prove that the influence of the crosstalk on the electrochemical performance of LTO is limited.

The understanding of surface reactions at the electrode-electrolyte interfaces has been a longstanding challenge in Li-ion batteries. X-ray photoemission electron microscopy is used to throw light on the disputed aspects of the surface reactivity of high-energy Li-rich Li

Photoelectrochemical solar water splitting is a promising approach to convert solar energy into sustainable hydrogen fuel using semiconductor electrodes. Due to their visible light absorption properties, oxynitrides have shown to be attractive photocatalysts for this application. In this study, the influence of the preparation method of CaNbO2N particles on their morphological and optical properties, and thereby their photoelectrochemical performance, is investigated. The best performing CaNbO2N photoanode is produced by ammonolysis of Nb enriched calcium niobium oxide. The enhanced photoactivity arises from an enlarged surface area and superior visible light absorption properties. The photoactivity of this photoanode was further enhanced by photodeposition of Co-Pi co-catalyst and by atomic layer deposition of an Al2O3 overlayer. A photocurrent density of 70 microA.cm-2 at 1.23 V vs RHE was achieved. The observed enhancement of the photoelectrochemical performance after Co-Pi/Al2O3 deposition is the combined effect of the improved kinetics of oxygen evolution due to the Co-Pi co-catalyst and the reduced surface recombination of the photogenerated carriers at the Al2O3 surface layer.

The near ambient pressure photoemission (NAPP) technique equipped with a liquid jet (LJ) is used for the first time to explore the electronic structure of the most commonly employed carbonate based Li-ion battery electrolytes. Experiments were performed at the SIM beamline of the Swiss Light Source (SLS) with the purpose of monitoring the Li-ion (Li+, Li 1s) solvation of 1M LiClO4 in 1:1 EC:DMC, both anhydrous and with the addition of 5 % H2O, and in DMSO. These electrolytes have high vapor pressures that prevent their study by traditional XPS and therefore necessitate the use of NAPP. Our measurements show differences in binding energies between the Cl 2p and Li 1s core levels (ΔE = Cl 2p3/2−Li 1s) between different solvents, in particularly between the EC:DMC and the DMSO. The addition of only 5 % H2O clearly influences the electronic structure in DMC:EC, but to a lesser extent than completely changing the solvent. Density functional theory (DFT) calculations of solvated Li+ structures within the solvent-separated ion pair (SSIP) model provide support to our experimental findings by revealing that the observed ΔE between solvents is directly related to the change in the electronic structure of the Li+ cation and ClO4 − anion due to the modification of the solvation shell. This study establishes LJ NAPP as a powerful analytical method for the study of Li+ solvation that will prove complementary to the more established approaches of FTIR and NMR, but at the same time will allow for new experiments that cannot yet be realized by FTIR and NMR.

The facile one-pot synthesis of CeO2-based catalysts has been developed to prepare a relatively large amount of nanopowders with relevant catalytic activity towards CO oxidation. The method consists of a two-steps process carried out in ethylene glycol: in the first step, 5 nm well-crystallized pure CeO2 is prepared. In a subsequent second step, a salt of a noble metal is added to the CeO2 suspension and the deposition of the noble metal on the nanocrystalline CeO2 is induced by heating. Two catalysts were prepared: Pt/CeO2 and Au/CeO2. The as-prepared catalysts, the thermally treated catalysts, as well as the pure CeO2, are characterized by XRD, TGA, XPS, FTIR, HR-TEM, STEM, particle size distribution, and N2-physisorption. In spite of the identical preparation protocol, Au and Pt behave in a completely different way: Au forms rather large particles, most of them with triangular shape, easily identifiable and dispersed in the CeO2 matrix. In contrast, Pt was not identified as isolated particles. The high resolution X-ray diffraction carried out on the Pt/CeO2 thermally treated sample (500 degrees C for 1 h) shows a significant CeO2 lattice shrinkage, which can be interpreted as an at least partial incorporation of Pt into the CeO2 crystal lattice. Moreover, only Pt2+ and Pt4+ species were identified by XPS. In literature, the incorporation of Pt into the CeO2 lattice is supported by first-principle calculations and experimentally demonstrated only by combustion synthesis methods. To the best of our knowledge this is the first report where ionically dispersed Pt into the CeO2 lattice is obtained via a liquid synthesis method. The thermally treated Pt/CeO2 sample revealed good activity with 50% CO conversion at almost room temperature.

SnO

Organic carbonates are the predominant electrolyte base used in the best Li- and Na-ion battery systems. However, to date, their precise interactions with the electrode are not fully understood. Here, we elucidate the role of a prototypical electrolyte additive, fluoroethylene carbonate (FEC), in Na-ion batteries and illustrate its influence on the solid electrolyte interphase (SEI) composition. Through the use of bulk and surface analytical techniques, we find that early FEC decomposition forms a surface-passivating constituent (Na2CO3), reduces the rate of decomposition of the propylene carbonate electrolyte, and supports the preservation of the polyvinylidene difluoride (PVDF) binder. Furthermore, we observe that NaF is formed by the decomposing PVDF binder when no additive is present, resulting in the early degradation of battery performance. This new understanding of the SEI offers greater chemical insight into the selection of binder and electrolyte combinations, allowing better targeted use of thes...

The volatile alane (H2AlO t Bu)2 decomposes into amorphous HAlO or Al0@Al2O3 nanoparticles upon heating, depending on the time and temperature. By coating the Ni-rich cathode material NCM851005 with this compound, the NCM’s cycling stability and electric conductivity were increased. Thus, the coating not only yielded Al0@Al2O3 nanoparticles but also, by reaction with surface Li2O/LiOH/Li2CO3, a Li+ conductive LiAlO2 layer. The coatings with 0.3 and 0.1 wt% (H2AlO t Bu)2, respectively, significantly reduced the resistance build-up to 70/115% after 280 cycles at 1 C (351% without coating). Upon treatment of the 0.3 wt% Al-coating with two equivalents of anhydrous HF, the Al2O3 and LiAlO2 parts were transformed into a Li[AlO(OH)F] layer, which yielded better capacity retention, retaining the low impedance build-up of only +120% (280 cycles at 1 C). This treatment, however, proved to have the same effect as simply reducing the amount of (H2AlO t Bu)2 for the coating to 0.1%.

The preparation of nanoparticles with tailored properties and in quantities in the order of 10–100 g prepared with laboratory-scale equipment is a target of great interest. In this study, Ni nanoparticles with different sizes, surface morphologies, magnetic, and catalytic properties were obtained from NiCl2, N2H4, NaOH, and ethylene glycol as solvent by tuning the synthesis parameters. Preliminary syntheses were done in batch reactors and then the continuous synthesis carried out in the Segmented Flow Tubular Reactor (SFTR). For the first time a SFTR system was applied to a non-aqueous system. By combining SEM, HRTEM, XRD, TGA, XPS, FTIR, specific surface area, SQUID, and catalytic tests, the complete structural, morphological, and functional characterization of the produced nanoparticles were performed. The continuous production of 2.1 g h−1 of Ni nanoparticles was carried out up to 6 h without product properties deterioration. The results allow estimating a production >300 g d−1 in an ad-hoc low-cost single-tube SFTR system. Catalytic tests of CO methanation showed good activity at 769 K with stable methane yield of 83%. The results presented in this study demonstrate that reliable and reproducible synthesis of relatively high amounts of metal nanoparticles with lab-scale equipment can be achieved. This approach opens new opportunities for reliable and controlled preparation of advanced materials in quantities suitable for a full functional characterization.

Lithium-rich mixed metal layered oxides constitute a large class of promising high-potential positive electrode materials in which higher specific charges are accessed only by activation of the Li2MnO3 domains. During the activation, oxygen is extracted from the oxide and evolves at the electrode–electrolyte interface. Differential electrochemical mass spectrometry was employed to follow volatile species developed during cycling. Although typical Li-ion aprotic carbonate electrolytes already suffer from oxidative decomposition at high potentials, the presence of O2 is here confirmed to enhance its reactivity. During the first cycle, O2 and CO2 evolve and their respective amounts vary as a function of the cycling conditions. However, for ethylene carbonate-based electrolytes, the amount of O2 and CO2 is found to be independent of the electrolyte composition. Moreover, X-ray photoelectron spectroscopy revealed that carbon-based components of the solid layers are dissolved between 3.0 and 4.0 V versus Li+/Li...

For the successful employment of Li-ion batteries at large scale, e.g. for electrical vehicles or stationary energy storage, a crucial point to be solved is the development of safer, non-flammable batteries. For that purpose, the currently used carbonate-based liquid electrolyte has to be substituted with a non-flammable material such as solid-state electrolytes. In particular, (Li2S)3-P2S5 (LPS) is among the promising solid electrolyte (SE) materials showing a good ion conductivity at room temperature (~ 0.4 mS/cm)1. Another improvement that is also needed in the near future concerns the energy density of the battery. In order to increase this parameter, anode conversion-alloy materials, such as SnO2, are a serious choice, with a specific capacity of ~ 1500 mAh/g. Despite the theoretical predictions of the different SnO2 conversion and alloy reactions during (de-)lithiation, the experimental identification of those electrochemical reactions and the formation of intermediate species (e.g. LiaSnOb, LixSn and Li2O) is not fully understood2, mainly due to their possible relaxation and conversion to other byproducts during disassembling of the cycled cell in post mortem analysis3. Li2O, in particular, converts into the more stable Li2CO3 phase in presence of traces of CO2. In this contribution, we will show how we recently developed operando X-ray photoelectron spectroscopy (o-XPS) method, offering an unprecedented manner of monitoring in real time the evolution of the electrolyte-electrode interface and the (de-)lithiation processes of the active materials during solid state Li-ion battery operation4. In this study, o-XPS is employed to investigate the (de-)lithiation of the SnO2 particles in a working electrode composed of SnO2 nanoparticles, LPS SE and Super P as conductive carbon cycled versus InLix counter electrode (Figure 1a). The analysis of the Sn 3d (Figure 1b), Sn 4d, O 1s (Figure 1c) and Li 1s spectra reveals the progressive conversion of the SnO2 particles to form Sn0 and the simultaneous formation of the LixSn alloy. When the potential is below 0.4 V (vs. Li+/Li), the Li2O phase is formed and grows until the full lithiation at 0.01 V (vs. Li+/Li), where the only species observed are Li2O and LixSn. By avoiding the conversion of Li2O to Li2CO3, we are also able to follow the de-lithiation process, confirming the reversibility of the conversion-alloy reactions where LixSn is converted to SnOx at 2.3 V (vs. Li+/Li). The S 2p and P 2p core levels reveal the presence of reduced Li2S byproduct species below 1.6 V (vs. Li+/Li), in accordance with previous studies1. The knowledge gained with o-XPS on the (de-)lithiation processes of SnO2 and the stability of the SnO2-LPS interface is crucial to understand the mechanism leading to capacity loss during cycling and help to design a better cycling protocols for the SnO2 electrodes in solid-state batteries. References: Wu, M. El Kazzi, C. Villevieille, J. Electroceram., 2017, 38, 207-214 Cheng, A. Nie, L.-Y. Gan, Q. Zhang, U. Schwingenschlögi, J. Mater. Chem. A, 2015, 3, 19483 Ferraresi, C. Villevieille, I. Czekaj, M. Horisberger, P. Novák, M. El Kazzi, ACS Appl. Mater. Interfaces, 2018, 10, 8712-8720 X. Wu, C. Villevieille, P. Novák, M. El Kazzi, Phys. Chem. Chem. Phys., 2018, 20, 11123 Figure 1

The development of the next generation high-energy density Li-ion batteries requires a deep understanding on the interface between high voltage cathode and electrolyte. When cathode materials are cycled to high potential, especially above 4.3 V vs. Li+/Li, different reactions can take place at the cathode-electrolyte interface: electrolyte oxidation1, surface structural changes, dissolution of the transition metals (TMs)2, oxygen oxidation3 and release4, and binder degradation5. Moreover, all those parasitic reactions can also affect the counter electrode via a "cross-talk" process of organic/inorganic species and TMs. To elucidate these complex reaction mechanisms, a combination of different spectroscopy techniques is required in order to have full picture of the interface reactivity. Although X-ray photoelectron spectroscopy (XPS) provides valuable knowledge concerning the binder and electrolyte stability, information about the TMs oxidation states and the surface structure are more difficult to obtain. On the other hand, X-ray absorption spectroscopy (XAS) of TM L-edges, C K and O K-edges provides very important knowledge on the oxidation states and structural evolution during cycling. By combining the high lateral resolution and surface sensitivity of X-ray photoemission electron microscopy (XPEEM)6 with total electron yield (TEY) and total fluorescence yield (TFY), one can gain a better understanding of the evolution of both the surface and the bulk of the particles. In this contribution, we show the successful combination of XPS, XPEEM and XAS in TEY and TFY modes to elucidate the complex surface reactivity of LiNi0.8Co0.15Al0.05O2 (NCA) when it is cycled versus Li4Ti5O12 (LTO), especially at 4.9 V vs. Li+/Li in LP30 electrolyte. Our results show the instability at high potential of the organic binder contained in the electrodes and the LiPF6 salt in the electrolyte, while EC:DMC oxidation byproducts are not observed on neither the cathode nor the anode despite the high potential. Reduced Ni is detected on the NCA surface and, due to the limited oxygen release observed from the NCA material7, reversible oxygen oxidation is observed in the O K-edge spectra at the NCA surface, proving the participation of O together with Ni in the redox process of NCA at high potential (Figure 1a,b). The cubic-like NiO structure is also visible in the O K-edge caused by structural change. Despite the presence of Ni, Co and LiF on the LTO surface (Figure 1c), due to the instability of reduced TMs and the LiPF6/binder at the cathode-electrolyte interface, their influence on the electrochemical performances of LTO is limited. Instead, the overall fading of the NCA vs. LTO cell is mainly attributed to the structural degradation of the NCA particles. References: A. Guéguen, D. Streich, M. He, M. Mendez, F. F. Chesneau, P. Novák, E. J. Berg, J. Electrochem. Soc., 2016, 163(6), A1095-A1100. D. Leanza, C. A. F. Vaz, G. Melinte, X. Mu, P. Novák, M. El Kazzi, ACS Appl. Mater. Interfaces, 2019, 11(6), 6054-6065. G. Assat, D. Foix, C. Delacourt, A. Iadecola, R. Dedryvère, J.-M. Tarascon, Nat. commun., 2017, 8(1), 2219. D. Streich, C. Erk, A. Guéguen, P. Müller, F.-F. Chesneau, E. J. Berg, J. Phys. Chem. C, 2017, 121, 13481-13486. L. Bodenes, R. Dedryvère, H. Martinez, F. Fischer, C. Tessier, J.-P. Pérès, J. Electrochem. Soc., 2012, 159(10), A1739-A1746. D. Leanza, C. A. F. Vaz, I. Czekaj, P. Novák, M. El Kazzi, J. Mater. Chem. A, 2018, 6, 3534. E. Flores, N. Vonrüti, P. Novák, U. Aschauer, E. J. Berg, Chem. Mater., 2018, 30(14), 4694-4703. Figure 1