A Strategy towards Light-Absorbing Coatings Based on Optically Black Nanoporous Alumina with Tailored Disorder

This work provides a conceptually new way of thinking about the light-absorbing mechanism in additive-free black porous anodic alumina (black PAA, or b-PAA) layers obtained via “burning” anodizing regime. The new insight into the controllable photonic effects in PAA allows the implementation of the optical blackening method based on the deliberate randomization of the initially well-ordered nanopore arrangement. The proposed black coloration mechanism rests solely on the destructive interference of light after its multiple scattering. Similar effects have been earlier considered for some natural or artificially created biomimetic structures (e.g., the so-called “moth eye effect”, or the coloration mechanism in the Neurothemis tullia dragonfly wings). Comprehensive analysis confirmed that the chemical composition of b-PAA has only a minor influence on the color changes and the optical density increase, and that the light-absorbing properties most likely result from the structural effects. The new functional 2D materials exhibit strong adhesion to aluminum surface, are cost-effective and suitable for application under harsh thermal or UV-light conditions. They are potentially useful for manufacturing of optical devices or heat-resistant coatings in aerospace technologies, as well as solid supports for biological filtration and fluorescence imaging

High-temperature structure of Co3O4: Understanding spinel inversion using in situ and ex situ measurements

International audienc

Synthetic Tailoring of Ionic Conductivity in Multicationic Substituted, High‐Entropy Lithium Argyrodite Solid Electrolytes

Superionic conductors are key components of solid‐state batteries (SSBs). Multicomponent or high‐entropy materials, offering a vast compositional space for tailoring properties, have recently attracted attention as novel solid electrolytes (SEs). However, the influence of synthetic parameters on ionic conductivity in compositionally complex SEs has not yet been investigated. Herein, the effect of cooling rate after high‐temperature annealing on charge transport in the multicationic substituted lithium argyrodite Li₆.₅[P₀.₂₅Si₀.₂₅Ge₀.₂₅Sb₀.₂₅]S₅I is reported. It is demonstrated that a room‐temperature ionic conductivity of ∼12 mS cm⁻¹ can be achieved upon cooling at a moderate rate, superior to that of fast‐ and slow‐cooled samples. To rationalize the findings, the material is probed using powder diffraction, nuclear magnetic resonance and X‐ray photoelectron spectroscopy combined with electrochemical methods. In the case of moderate cooling rate, favorable structural (bulk) and compositional (surface) characteristics for lithium diffusion evolve. Li₆.₅[P₀.₂₅Si₀.₂₅Ge₀.₂₅Sb₀.₂₅]S₅I is also electrochemically tested in pellet‐type SSBs with a layered Ni‐rich oxide cathode. Although delivering larger specific capacities than Li₆PS₅Cl‐based cells at high current rates, the lower (electro)chemical stability of the high‐entropy Li‐ion conductor led to pronounced capacity fading. The research data indicate that subtle changes in bulk structure and surface composition strongly affect the electrical conductivity of high‐entropy lithium argyrodites

Dynamic behaviour of interphases and its implication on high-energy-density cathode materials in lithium-ion batteries

Undesired electrode-electrolyte interactions prevent the use of many high-energy-density cathode materials in practical lithium-ion batteries. Efforts to address their limited service life have predominantly focused on the active electrode materials and electrolytes. Here an advanced three-dimensional chemical and imaging analysis on a model material, the nickel-rich layered lithium transition-metal oxide, reveals the dynamic behaviour of cathode interphases driven by conductive carbon additives (carbon black) in a common nonaqueous electrolyte. Region-of-interest sensitive secondary-ion mass spectrometry shows that a cathode-electrolyte interphase, initially formed on carbon black with no electrochemical bias applied, readily passivates the cathode particles through mutual exchange of surface species. By tuning the interphase thickness, we demonstrate its robustness in suppressing the deterioration of the electrode/electrolyte interface during high-voltage cell operation. Our results provide insights on the formation and evolution of cathode interphases, facilitating development of in situ surface protection on high-energy-density cathode materials in lithium-based batteries.ope

Dissociative adsorption of H2O on LiCoO2 (00l) surfaces: Co reduction induced by electron transfer from intrinsic defects

Understanding the mechanism of the interaction of lithium ion conductors with water is crucial for both fundamental and technological points of view. Despite the generally accepted fact that water is one of main sources of the degradation of Li ion recharge batteries, the physicochemical processes occurring at the water lithium ion conductor interface are not fully understood. By using synchrotron X ray photoelectron spectroscopy SXPS and O K and Co L X ray absorption near edge structure XANES , we evidence that H2O is dissociatively adsorbed on LiCoO2 thin film at room temperature resulting in the formation of OH groups and the accumulation of the negative charge at the surface accompanied by electron transfer to the initial empty Co3d e amp; 8727;g state. By considering the experimentally obtained energy diagram of the ionic conductor and water, direct charge transfer is not favorable due to a high difference in the chemical potential of the ionic conductor and electronic levels of the molecule. Here, we develop the model for the dissociative water adsorption which explains the electron transfer to LiCoO2 by using the atomistic approach. The model takes into account the intrinsic defects found on the surface lt;2 nm depth by using the depth resolved photoemission experiments and can be explored to other layered transition metal oxides to interpret the interaction of water with the surface of ionic conductors. Published by AIP Publishin

LiMO2 (M = Ni, Co) thin film cathode materials: A correlation between the valence state of transition metals and the electrochemical properties

The electronic properties of the LiMO2 (M = Ni, Co) thin film cathode materials grown by RF sputtering/co-sputtering are in situ studied by X-ray photoelectron spectroscopy (XPS). Stoichiometric Li1.0Co1.0O2 thin films deposited on a heated substrate at T = 500–550 °C reveal the Co3+ (t2g6eg0) ground state configuration in the low spin (LS) state. Stoichiometry of the Lix(Ni,Co)O2 films and the valence and spin states of the Ni ions depend strongly on the growth conditions. The electronic configuration of stoichiometric Li1.0Ni0.5Co0.5O2 is described as the Ni3+ (t2g6eg1) LS and Co3+ (t2g6eg0) LS states. The Li-deficient Lix<1.0(Ni,Co)O2 exhibits Ni2+ (t2g6eg2) in the high spin (HS) and Co3+ (t2g6eg0) in LS states. The reduction of the trivalent Ni ions to Ni2+ (t2g6eg2) with a HS state electronic configuration is related to the evaporation of Li2O at elevated substrate temperatures coupled to a loss of O2 due to an internal oxidation reaction of O2− lattice ions induced by the strongly oxidizing Ni3+ ions. Owing to the stable Co3+ (t2g6eg0) with a LS state electronic configuration, Li1.0Co1.0O2 thin films cycled to 4.2 V exhibit a very good electrochemical reversibility. Li1.0Ni0.5Co0.5O2 films annealed at the same temperature as for Li1.0Co1.0O2 manifest a broadening of the oxidation/reduction peaks of the cyclic voltammogram (CV) curves with a strong current drop after the first step of the electrochemical Li-deintercalation. The observed irreversibility of the Li-intercalation/deintercalation process is attributed to instability of the Ni3+ (t2g6eg1) ions. Temperatures of the deposition/annealing above 750 °C lead to the phase separation of the Lix(Ni,Co)O2 films, a strong Li deficiency, the occurrence of Co2+ (t2g5eg2) with HS ions and consequently a complete degeneration of the electrochemical cyclability

Preparation and characterization of carbon foams–LiCoPO4 composites

The preparation and characterization of composites consisting of carbon foams coated with olivine structured lithium cobalt phosphate is reported. The composites are prepared by a Pechini assisted sol–gel process and treated under different conditions in flowing nitrogen and in flowing air. The structural, morphological and electrochemical properties were found to be dependent upon the annealing conditions as time and atmosphere. After annealing in nitrogen, the formation of the LiCoPO 4 phase on the foams is observed at T = 730 ◦ C. The photoelectron emission spectra reveal divalent cobalt ions in the composites. The LiCoPO 4 /foam composites deliver a discharge specific capacity of 100 mAh g – 1 , at a discharge rate of C/25 and room temperature. After a pre-annealing in air then the annealing in nitrogen, the voltammetric curves show values of the reduction/oxidation processes at 4.6 V and 5.2 V respectively. The electrochemical measurements revealed a decrease of the capacity fade ( ∼ 26% at C/10, RT). A plateau in the specific capacity as a function of the potential has been observed

Adsorption of Diethyl Carbonate on LiCoO2 Thin Films Formation of the Electrochemical Interface

Despite numerous efforts to elucidate interface-related phenomena of Li ion battery cathodes, the exact nature of cathode/electrolyte interfaces is still not fully resolved. Key factors for the properties of semiconducting ionic electrodes are band bending and energy level alignment at the interface, which have not been given much attention in the past. In this contribution, we investigate the formation of the electrochemical interface for a LiCoO2 electrode in contact with a solvent adsorbate phase by a surface science approach. Diethyl carbonate (DEC) was adsorbed stepwise onto a LiCoO2 thin film electrode and the electrode surface analyzed with X-ray photoelectron spectroscopy (XPS) after each adsorption step. Adsorption results in the formation of a charged layer in the electrode, which we attribute to the transfer of lithium ions from the electrode to the adsorbed phase. The offset between the LiCoO2 valence band and HOMO of the adsorbed DEC is large (4 eV) under the experimental conditions, which renders solvent oxidation unlikely