Lithium ion battery degradation: what you need to know.

The expansion of lithium-ion batteries from consumer electronics to larger-scale transport and energy storage applications has made understanding the many mechanisms responsible for battery degradation increasingly important. The literature in this complex topic has grown considerably; this perspective aims to distil current knowledge into a succinct form, as a reference and a guide to understanding battery degradation. Unlike other reviews, this work emphasises the coupling between the different mechanisms and the different physical and chemical approaches used to trigger, identify and monitor various mechanisms, as well as the various computational models that attempt to simulate these interactions. Degradation is separated into three levels: the actual mechanisms themselves, the observable consequences at cell level called modes and the operational effects such as capacity or power fade. Five principal and thirteen secondary mechanisms were found that are generally considered to be the cause of degradation during normal operation, which all give rise to five observable modes. A flowchart illustrates the different feedback loops that couple the various forms of degradation, whilst a table is presented to highlight the experimental conditions that are most likely to trigger specific degradation mechanisms. Together, they provide a powerful guide to designing experiments or models for investigating battery degradation.

Self-organized spreading of droplets to fluid toroids.

HYPOTHESIS: Mixing of a chemical trigger of lower surface tension into a microdroplet with relatively higher surface tension can cause a rapid spreading of the droplet on a liquid-sublayer to form a host of metastable liquid morphologies such as sheets, toroids, threads, or droplets. Subsequently, such metastable fluidic objects break into a collection of droplets to form microemulsions. EXPERIMENTS: Introduction of surfactant loaded water or long-chain alcohols into an oleic acid microdroplet stimulate a rapid spreading of the same on a water sublayer, which helps in the formation of a metastable liquid sheet connected to a liquid toroid. Much like slipping films, the liquid sheet dewets the water underlayer through the formation of holes before they grow and coalesce to form liquid ribbons. While such liquid structures eventually break into an array of microdroplets, the liquid toroid expands before undergoing a Plateau-Rayleigh instability to form microdroplets. FINDINGS: A single step self-organization process in which a chemical trigger can convert a microdroplet into a liquid-toroid on a water surface, in absence of any rotational influence. A symmetric to asymmetric transition in toroid morphology is observed due to the changeover of laminar to turbulent flow regimes with the reduction in viscosity of fluid-sublayer or variation in chemical triggers. The toroid cross-section and droplet spacing after the toroid breakup follow a length scale evaluated from a linear stability analysis.

One-pot synthesis of Cr(III)-incorporated Zr(IV) oxide for fluoride remediation: a lab to field performance evaluation study.

A low-cost Cr(III)-incorporated Zr(IV) bimetallic oxide (CZ) was synthesized by simple chemical precipitation method for removal of fluoride from contaminated water. The physicochemical properties of CZ before and after fluoride removal were established with several instrumental techniques such as TEM with elemental mapping, SEM with EDX, XRD, IR, XPS, zeta potential measurement, etc. Batch adsorption technique were carried out to understand the factors affecting fluoride adsorption, such as effects of initial pH, adsorbent dose, co-occurring ions, contact time, and temperature. The maximum adsorption capacity observed at pH between 5 and 7. The fluoride adsorption processes on CZ obeyed the pseudo-second-order rate equations and both Freundlich and DR isotherm models. The maximum adsorption capacity of 90.67 mg g-1 was obtained. The thermodynamic parameters ΔH0 (positive), ΔS0 (positive), and ΔG0 (negative) indicating the fluoride sorption system was endothermic, spontaneous, and feasible. The CZ also successfully used as fluoride adsorbent for real field contaminated water collected from the Machatora district, Bankura, West Bengal, India. Graphical abstract Schematic representation of CZ synthesis and its application for lab as well as field water purification purpose.

Fabrication of pixelated liquid crystal nanostructures employing the contact line instabilities of droplets.

A liquid crystal (LC) droplet resting on a poly-dimethylsiloxane substrate could rapidly spread upon solvent vapour annealing to form a non-uniform film. While the solvophobic surfaces restricted the spreading of the droplet to form a thicker film upon solvent annealing, the solvophilic substrates allowed the formation of a thinner film under similar conditions. Withdrawal of the solvent exposure caused rapid evaporation of the solvent molecules from the film, especially near the retracting contact-line to form microscale LC-droplets, which shrunk into nanoscopic ones after evaporation of the excess solvent. The thinner films on solvophilic surfaces allowed the formation of droplets with smaller size and periodicity as small as ∼100 nm and ∼200 nm, respectively. Furthermore, the use of a patterned substrate could impose a large-area ordering on the nanodroplets. A theoretical model for an evaporating film of LC-solution revealed that the spacing of nanodroplets could be decided by the interplay of stabilizing and destabilizing components of capillary force while van der Waals interaction played a supportive role when the film was ultrathin near the contact line. The micro/nanodroplets thus formed showed an anomalous oscillatory rotational motion originating from the difference in the Laplace pressure near contact lines under the influence of an external electric field. The application of the Lorenz force to these droplets showed translation and rotational motions followed by ejection of satellite droplets.

Calcium ion incorporated hydrous iron(III) oxide: synthesis, characterization, and property exploitation towards water remediation from arsenite and fluoride.

Calcium ion-incorporated hydrous iron(III) oxide (CIHIO) samples have been prepared aiming investigation of efficiency enhancement on arsenic and fluoride adsorption of hydrous iron(III) oxide (HIO). Characterization of the optimized product with various analytical tools confirms that CIHIO is microcrystalline and mesoporous (pore width, 26.97 Å; pore diameter, 27.742 Å with pore volume 0.18 cm3 g-1) material. Increase of the BET surface area (> 60%) of CIHIO (269.61 m2 g-1) relative to HIO (165.6 m2 g-1) is noticeable. CIHIO particles are estimated to be ~ 50 nm from AFM and TEM analyses. Although the pH optimized for arsenite and fluoride adsorptions are different, the efficiencies of CIHIO towards their adsorption are very good at pH 6.5 (pHzpc). The adsorption kinetics and equilibrium data of either tested species agree well, respectively, with pseudo-second order model and Langmuir monolayer adsorption phenomenon. Langmuir capacities (mg g-1at 303 K) estimated are 29.07 and 25.57, respectively, for arsenite and fluoride. The spontaneity of adsorption reactions (ΔG0 = - 18.02 to - 20.12 kJ mol-1 for arsenite; - 0.2523 to - 3.352 kJ mol-1 for fluoride) are the consequence of entropy parameter. The phosphate ion (1 mM) compared to others influenced adversely the arsenite and/or fluoride adsorption reactions. CIHIO (2.0 g L-1) is capable to abstract arsenite or fluoride above 90% from their solution (0 to 5.0 mg L-1). Mechanism assessment revealed that the adsorption of arsenite occurs via chelation, while of fluoride occurs with ion-exchange.

Electric field mediated elastic contact lithography of thin viscoelastic films for miniaturized and multiscale patterns.

Elastic contact lithography (ECL) and electric field lithography (EFL) have both shown significant potential to develop large-area micropatterns on polymeric surfaces. Recently, the major challenges associated with these processes have been the improvement of the aspect ratio and reduction in the size and periodicity of the patterns fabricated. Herein, with the help of non-linear simulations, we show that combining these methods can be one recipe to overcome these limitations. We consider a linear viscoelastic film for the linear and non-linear analyses. In this regard, we explore the role of the moving contactor to improve the aspect ratio of the patterns. The study uncovers that (i) combined destabilizing influences originating from van der Waals and electric field forces ensure smaller timescales and length scales for the instabilities, (ii) the aid from the electric field helps to improve the minimum separation distance so that the contact instability initiates at a larger separation distance, (iii) a long-range ordering can be inflicted on the patterns on the polymer surfaces when electrodes with periodic physicochemical patterns are used and (iv) the strength of the externally applied electric field and the ratio of elastic to viscous compliance of the film play crucial roles in deciding the different modes of debonding of the film - peeling, catastrophic or coalescence. The proposed method can improve the aspect ratio of patterns by ∼9-fold during the peeling mode of debonding. Furthermore, pathways to develop technologically important biomimetic surfaces with multiscale and hierarchical structures have been shown.

Pattern-Directed Ordering of Spin-Dewetted Liquid Crystal Micro- or Nanodroplets as Pixelated Light Reflectors and Locomotives.

Chemical pattern directed spin-dewetting of a macroscopic droplet composed of a dilute organic solution of liquid crystal (LC) formed an ordered array of micro- and nanoscale LC droplets. Controlled evaporation of the spin-dewetted droplets through vacuum drying could further miniaturize the size to the level of ∼90 nm. The size, periodicity, and spacing of these mesoscale droplets could be tuned with the variations in the initial loading of LC in the organic solution, the strength of the centripetal force on the droplet, and the duration of the evaporation. A simple theoretical model was developed to predict the spacing between the spin-dewetted droplets. The patterned LC droplets showed a reversible phase transition from nematic to isotropic and vice versa with the periodic exposure of a solvent vapor and its removal. A similar phase transition behavior was also observed with the periodic increase or reduction of temperature, suggesting their usefulness as vapor or temperature sensors. Interestingly, when the spin-dewetted droplets were confined between a pair of electrodes and an external electric field was applied, the droplets situated at the hydrophobic patches showed light-reflecting properties under the polarization microscopy highlighting their importance in the development of micro- or nanoscale LC displays. The digitized LC droplets, which were stationary otherwise, showed dielectrophoretic locomotion under the guidance of the external electric field beyond a threshold intensity of the field. Remarkably, the motion of these droplets could be restricted to the hydrophilic zones, which were confined between the hydrophobic patches of the chemically patterned surface. The findings could significantly contribute in the development of futuristic vapor or temperature sensors, light reflectors, and self-propellers using the micro- or nanoscale digitized LC droplets.

Influence of the mutable kinetic parameters on the adhesion and debonding of thin viscoelastic films.

Detachment of a surface from a viscoelastic layer, such as a film of glue, engenders bridges between the surfaces until separation. Such surface instabilities arising during contact and detachment of viscoelastic films with rigid contactors have been theoretically explored by linear stability analysis and nonlinear simulations. The contact instabilities of viscoelastic materials are found to manifest in either a 'critical' or a 'dominant' mode in which the former is preferred when the contactor is slowly brought near the film while the latter manifests when the film is 'hard-pressed' against it. The nonlinear analysis considers the movement of contactor during adhesion-debonding cycle, which uncovers that the kinetic parameters can overshadow the thermodynamically predicted area of contact, average force for pull-off, energy of contactor-film separation, and pathways of debonding. Three distinct pathways of debonding - peeling, catastrophic column collapse, and column coalescence, are found to manifest with the variation in the ratio of the elastic to viscous compliances of the viscoelastic film. The study also reveals that in the dominant mode of instability, a smaller length scale with a larger area contact between the contactor and film can develop patterns having aspect ratio ∼10 times larger than the same obtained from elastic film.