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Probing the solid/liquid interface of batteries operando/in situ with ambient pressure X-ray photoelectron spectroscopy (APXPS) using the dip-and-pull method remains a challenging endeavor due to spatial and temporal variations in liquid layer shape, thickness, and composition. Monitoring the electrochemical and topographical nature of the liquid edge where the interface is accessed is essential to correctly interpret interfacial spectra. In this work, a methodology combining experimental design and software-based data processing for interface probing is reported. This experimental methodology utilizes continuous motion during fixed-mode APXPS measurements by periodically scanning across the dry electrode and thick electrolyte regions to capture the transitional interface. Two software-based approaches for retrieving the interface spectra are evaluated. In an analysis of the intensity attenuation pattern of a unique electrode signal, interface spectra are recognized at the edge of the intensity transition from electrode to electrolyte. The second method utilizes peak positions for interface identification. Selected spectra with the same peak energies also exhibit the same chemical features, indicating the close correlations between the interface energetics and local chemical compositions. Further, topographical information can be extracted using scanning APXPS by translating spectral intensities into liquid thickness, creating a spectro-microscopic 3D image of the liquid edge region. In the examined systems, the thickness of a propylene carbonate electrolyte edge on both lithium cobalt oxide and gold WE surfaces exhibits a step-jump transition from the thin to thick liquid region. The liquid distribution is also shown to depend on the morphological and chemical nature of the electrode. The imaging provides a better understanding of the relationship between liquid distribution and probed interface features while validating the functionality of the setup.

Binders are essential components in battery systems that maintain the electrode structure and integrity throughout cycling. The choice of binder affects processing, electrochemical behavior, and end-of-life recovery. The widely used poly(vinylidene difluoride) (PVDF) binder is increasingly scrutinized since it is a polyfluoroalkyl compound and requires processing in organic solvents like N-methyl-2-pyrrolidone. Consequently, efforts are underway to identify more sustainable options. In this work, we present chitin nanofibers (ChNFs), derived from fisheries waste, as a biobased, fluorine-free alternative that enables fully aqueous electrode fabrication. ChNFs disperse more than 90% of graphite in water without the need for auxiliary agents such as surfactants. Colloidal probe microscopy shows that adhesion between protonated ChNFs and graphite depends on pH, likely being governed by cation-π interactions. This strong affinity facilitates the remarkable dispersing capability of ChNFs through a multifaceted mechanism. Adsorbed nanofibers confer electro-steric stabilization by extension into the aqueous phase. The strong ChNF network can physically entrap larger particles, greatly enhancing the long-term stability of ChNF-graphite suspensions. The ChNF-graphite dispersion exhibits rheological behavior suited for forming uniform electrode coatings. Electrodes prepared with 4% ChNFs deliver specific capacities of 370 mA h g^-1 and enhanced capacity retention over 100 cycles compared to PVDF-based counterparts. Electron microscopy, X-ray photoelectron spectroscopy, and online electrochemical mass spectrometry analyses reveal that the nature of the binder dictates the solid electrolyte interphase (SEI) characteristics. The ChNF produces a more robust and stable SEI that suppresses electrolyte reduction, directly contributing to the enhanced electrochemical performance.

Silicon-based anodes offer substantially higher theoretical capacities than graphite in lithium-ion batteries, but their practical deployment is hindered by severe volume changes that induce mechanical degradation and unstable interfacial chemistry. While nanoscaling strategies can mitigate these effects, they often suffer from low tapped density, complex synthesis, and limited scalability. Porous silicon microparticles provide a promising alternative by partially accommodating volume expansion while preserving processability and electrode-level integrity. Here, a HF-free urea-assisted etching strategy is employed to generate porous silicon microparticles under mild conditions, leveraging the coupled action of thermally induced structural disruption and chemically driven surface modification. Control experiments confirm that the combined action of these effects is essential to achieve BJH-resolved mesoporosity and increased surface area. The resulting porous silicon exhibits oxygen- and nitrogen-containing surface functionalities. Composite electrodes prepared with nanographite and sodium alginate binder at graphite:silicon:binder ratios of 8:1:1, 7:2:1, and 4.5:4.5:1 demonstrate improved electrochemical behavior. In half-cell testing, electrodes containing 10-20 wt % porous silicon deliver stable redox activity and retain 630-880 mAh g^-1 after 100 cycles at 0.1 C, with Coulombic efficiencies of 98.8-99.7%, whereas higher silicon loadings lead to rapid capacity decay. Cycling-resolved impedance and differential-capacity analyses reveal the formation of a thicker yet mechanically resilient interphase that stabilizes charge-transfer kinetics, while rate capability tests show 65-74% capacity retention at 2 C.

Non-hydrolyzing salts such as lithium bis(fluorosulfonyl)imide (LiFSI) offer a promising strategy to develop water-tolerant electrochemical energy storage devices, potentially reducing production costs and energy consumption during cell manufacturing. In this work, the effectiveness of a LiFSI-based carbonate electrolyte is evaluated in the presence of deliberately added trace water (950, 2300, and 6000 ppm H2O) within a Li-ion capacitor (LIC) composed of activated carbon (AC) positive and pre-lithiated graphite (Gr) negative electrodes. The electrochemical performance and aging behavior of the electrodes are systematically assessed and compared to the dry electrolyte (<12 ppm H2O). Remarkably, 950 ppm H2O does not significantly affect capacity retention or aging during galvanostatic cycling of the LIC, nor during voltage hold tests of AC electrodes at 3.95 V vs. Li/Li+. In contrast, higher water concentrations (2300 and 6000 ppm H2O) induce substantial parasitic processes, including reduced initial capacity and capacity retention, reduced coulombic efficiency, increased impedance on both electrodes, and extensive lithium inventory loss on the Gr electrode. Post-mortem XPS and SEM analyses attribute these side effects to water-promoted oxidative and reductive decomposition of the LiFSI salt, as well as solvent hydrolysis, which thickens and increases the resistance of the solid electrolyte interphase (SEI) on the Gr electrode.

X-ray photoelectron spectroscopy (PES) has been widely applied in the field of battery studies. However, the lack of knowledge regarding the inelastic mean free path (IMFP) for studied systems limits the interpretation of spectroscopic results. In this work, the IMFP of poly(trimethylene carbonate) (PTMC), poly( epsilon-caprolactone) (PCL), and the solid polymer electrolytes consisting of lithium bis(oxalate)borate (LiBOB) together with PTMC or PCL has been determined using PES at a photoelectron kinetic energy of 8.7 keV. Additionally, the surface roughness of these films was investigated by atomic force microscopy and correlated with calculated IMFP values. Our studies reveal that the IMFP of solid polymer electrolytes is higher than that of pure polymers. The presented IMFPs provide references for future spectroscopic studies involving these materials.

Ambient pressure X-ray photoelectron spectroscopy (APXPS) combined with the dip-and-pull method can be used for operando studies of electrochemical systems. A complete coupling between the spectroscopic and the electrochemical measurements is generally challenging due to an inherent difference between the meniscus and the bulk electrolyte - the mass transport. This work investigates meniscus mass transport and its effect on the meniscus electrochemical processes by simultaneously conducting time-resolved APXPS and chronoamperometry for two types of electrochemical processes: capacitive and faradaic. Additionally, experiments are complemented with simulations based on a purposefully constructed transmission line model. In the investigated system, based on a gold electrode and carbonate electrolyte, the meniscus resistance is shown to be over 1000 times larger than the bulk electrolyte resistance. Consequently, during faradaic processes, considerable iR drop in the meniscus results in two to three orders of magnitude slower rate of charge transfer in the meniscus than in the bulk electrolyte. Using the acquired understanding of the meniscus mass transport, we suggest an experimental practice to quantify the iR drop and propose possible remedies for experiments where any impact of the iR drop must be avoided.

The surface chemistry of mesoporous nickel oxide (NiOx) plays a pivotal role in its functionality across various technological applications. Herein, we present a detailed study of NiOx surface states using multiple spectroscopic techniques, including ambient pressure X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-vis) spectroscopy, and Fourier-transform infrared (FTIR) spectroscopy, to observe the removal and reformation of surface species during gas dosing. Our findings reveal the presence of both surface oxygen- and hydroxide-species on the NiOx surface. Furthermore, the results suggest that NiO_x surface states consist of approximately 50% hydroxides and the remainder comprising adsorbed oxygen species, likely predominantly diatomic oxygen ions (O₂⁻), that are associated with higher valence Ni states (Ni³⁺). In situ experiments demonstrate that the formation and stability of hydroxides and diatomic oxygen ions depend on temperature and are significantly influenced by interactions with atmospheric oxygen and water. Our insights into the NiO_x surface state composition and reactivity offer a nuanced understanding of its surface chemistry, with implications for enhancing its performance in catalysis, sensing, energy harvesting and energy storage devices where the surface states of nickel oxide are known to dictate electronic and chemical properties of the material.

Solid composite polymer electrolytes (CPEs) are complex mixtures of ceramics, polymers, and lithium salts, where the interfaces between the different phases play an important role for stability, conductivity, and compatibility with electrode materials. In this study, two interfacial phenomena of CPEs consisting of lithium lanthanum zirconium oxide (LLZO) ceramic fillers in poly(trimethylene carbonate) (PTMC) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt are studied. First, the LLZO-polymer electrolyte interfaces are investigated. Second, the stability of this CPE material vs a Li-metal electrode is explored, by employing soft X-ray photoelectron spectroscopy (PES) in combination with in situ deposition of Li. Three different LLZO loadings in PTMC are investigated: 30, 50, and 70 wt %. The concentration of LiTFSI follows that of the particle concentration at the surface of the samples, where the CPE with 50 wt % bulk content of LLZO exhibits the highest surface concentrations of both salt and ceramic. This shows an affinity for the salt at the LLZO surface. Furthermore, the stability of the CPEs against Li is studied after in situ Li deposition and shows that PTMC can decompose, potentially forming polypropylene at the CPE|Li interface, with the CPE at 50 wt % of LLZO showing the most pronounced PTMC and TFSI breakdown. This is in agreement with the observed properties for the polymer-ceramic interfaces and highlights the decisive role of LiTFSI accumulation on the surface of the ceramic particles, both for ionic transport and chemical stability.

The real-time interface chemistry between the lithium cobalt oxide (LCO) working electrode and the LiClO4/propylene carbonate (PC) electrolyte is investigated during lithiation/delithiation using dip-and-pull ambient pressure photoelectron spectroscopy (APXPS). The APXPS results appear to exhibit the seldom discussed Co2+ state in the LCO structure, where the operando measurements indicate electron transfer among Co2+, Co3+, and Co4+ states. Specifically, the lithiation of LCO reduces the Co4+ state to both Co3+ and Co2+ states, where, as a function of voltage, reduction to the Co2+ state is initially more pronounced followed by Co3+ formation. In addition, a delay in surface delithiation is observed during the reverse potential steps. This is discussed in terms of overpotential at the interface measurement position as a consequence of the dip-and-pull setup for this experiment. Finally, the shifts in the apparent binding energies of the spectral features corresponding to the electrolyte and LCO at their interface show that the electrochemical potentials at delithiation voltage steps are different from the lithiation steps at the same applied voltages. This further explains the non-responsive delithiation. The BE shift observed from the LCO surface is argued to be dominantly due to the semi-conductive nature of the sample. Overall, this article shows the importance of operando APXPS for probing non-equilibrium states in battery electrodes for understanding electron transfer in the reactions.

Nanostructured silicon oxides (SiOx) are close-to-market anode materials for increasing the energy density of next-generation lithium-ion batteries (LIBs), offering a balance between high capacity and enhanced cycling stability. However, achieving precise control over SiOx composition while maintaining structural integrity remains a challenge. In this study, we pioneer the use of nanostructured diatom-SiO2 frustules from industrially cultured Nitzschia sp. microalgae as a sustainable and tunable precursor for high-performance SiOx anodes via scalable magnesiothermic reduction reaction (MgTR). By optimizing the Mg-to-diatom-SiO2 molar ratio, we demonstrate controlled partial reduction of SiO2, yielding Si nanocrystals embedded within an SiO2 matrix. Notably, we reveal that the preservation of diatom-SiOx nanoporosity is highly sensitive to reaction exothermic conditions and is effectively stabilized by introducing NaCl as a heat scavenger. Tailoring the reactant composition (SiO2:Mg:NaCl = 1:1:2.5) resulted in anodes with superior electrochemical performance, delivering high capacity retention over 200 cycles. Through a comprehensive suite of characterization techniques, we establish the structure-property-performance relationships governing SiOx anode behavior. These findings mark a major advancement in sustainable SiOx anode design, providing a scalable strategy for integrating biologically templated nanostructures into high-performance LIBs.