Viscoelastic potential-induced changes in acoustically thin films explored by quartz crystal microbalance with motional resistance monitoring

Overview and Recent Advances in Hyphenated Electrochemical Techniques for the Characterization of Electroactive Materials

A hyphenated electrochemical technique consists of the combination of the coupling of an electrochemical technique with a non-electrochemical technique, such as spectroscopical and optical techniques, electrogravimetric techniques, and electromechanical techniques, among others. This review highlights the development of the use of this kind of technique to appreciate the useful information which can be extracted for the characterization of electroactive materials. The use of time derivatives and the acquisition of simultaneous signals from different techniques allow extra information from the crossed derivative functions in the dc-regime to be obtained. This strategy has also been effectively used in the ac-regime, reaching valuable information about the kinetics of the electrochemical processes taking place. Among others, molar masses of exchanged species or apparent molar absorptivities at different wavelengths have been estimated, increasing the knowledge of the mechanisms for different electrode processes.

Interphasial Engineering via Individual Moiety Functionalized Organosilane Single-Molecule for Extreme Quick Rechargeable SiO/NCM811 Lithium-Ion Batteries

The individual moiety-functionalized organosilane single molecule, that is, 1,1,1,5,5,5-hexamethyl-3-[(trimethylsilyl)oxy]-3-vinyltrisiloxane (TMSV), is investigated as an electrolyte additive for a less charge-consuming and viscoelastic solid electrolyte interphase (SEI) forming agent, finally accomplishing extremely quick (6 min) rechargeable SiO/NCM811 lithium-ion batteries. The moiety of the vinyl group serves with a poly(ethylene oxide)-like viscoelastic SEI film on the SiO electrode, which provides a physicochemically stable interphase during long-term cycling. The increase of DC-iR due to electrolyte decomposition on the continuously exposed SiO surface with cycling is inhibited by the alternated SEI composition. Degradation of bulk electrolyte solution caused by thermal decomposition of the LiPF₆ salt is also suppressed by the trimethylsilyl moiety in the TMSV additive, which scavenges HF. Owing to the multifunctionality of TMSV, the cycle performance of laminated pouch full cells comprising high-nickel-contented NCM811 positive electrode and SiO-enriched negative electrode is significantly improved at both room and elevated temperatures. Furthermore, the 6 min quick recharging cycle performance is also enhanced by the TMSV additive.

Making Advanced Electrogravimetry as an Affordable Analytical Tool for Battery Interface Characterization

Numerous sophisticated diagnostic techniques have been designed to monitor electrode-electrolyte interfaces that mainly govern the lifetime and reliability of batteries. Among them is the electrochemical quartz crystal microbalance (EQCM) that offers valuable insights of the interfaces once the required conditions of the deposited film in terms of viscoelastic and hydrodynamic properties are fulfilled. Herein, we propose a friendly protocol that includes the elaboration of a homogeneous deposit by spray coating followed by QCM measurements at multiharmonic frequencies to ensure the film flatness and rigidity for collecting meaningful data. Moreover, for easiness of the measurements, we report the design of a versatile and airtight EQCM cell setup that can be used either with aqueous or non-aqueous electrolytes. We also present, using a model battery material, LiFePO₄, how dual frequency and motional resistance monitoring during electrochemical cycling can be used as a well-suitable indicator for achieving reliable and reproducible electrogravimetric measurements. We demonstrate through this study the essential role of the solvent assisting lithium-ion insertion at the LiFePO₄ interface with a major outcome of solvent-dependent interfacial behavior. Namely, in aqueous media, we prove a near-surface desolvation of lithium ions from their water solvation shell as compared with organic molecules. This spatial dissimilarity leads to a smoother Li-ion transport across the LFP-H₂O interface, hence accounting for the difference in rate capability of LFP in the respective electrolytes. Overall, we hope our analytical insights on interfacial mechanisms will help in gaining a wider acceptance of EQCM-based methods from the battery community.

Quantification of porosity in extensively nanoporous thin films in contact with gases and liquids

Nanoporous layers are widely spread in nature and among artificial devices. However, complex characterization of extensively nanoporous thin films showing porosity-dependent softening lacks consistency and reliability when using different analytical techniques. We introduce herein, a facile and precise method of such complex characterization by multi-harmonic QCM-D (Quartz Crystal Microbalance with Dissipation Monitoring) measurements performed both in the air and liquids (Au-Zn alloy was used as a typical example). The porosity values determined by QCM-D in air and different liquids are entirely consistent with that obtained from parallel RBS (Rutherford Backscattering Spectroscopy) and GISAXS (Grazing-Incidence Small-Angle Scattering) characterizations. This ensures precise quantification of the nanolayer porosity simultaneously with tracking their viscoelastic properties in liquids, significantly increasing sensitivity of the viscoelastic detection (viscoelastic contrast principle). Our approach is in high demand for quantifying potential-induced changes in nanoporous layers of complex architectures fabricated for various electrocatalytic energy storage and analytical devices.

Thin porous layers are largely used, but a reliable method to quantify their porosity is missing. Here the authors demonstrate a method, based on quartz crystal microbalance measurements with dissipation monitoring, for accurate assessment of porosity and mechanical properties in thin porous films.