Mass transport in mixed-conducting LSCrF-ScSZ dual phase composites for oxygen transport membrane applications

The (La,Sr)(Cr,Fe)O3-δ (LSCrF)-Scandia-Stabilised Zirconia (ScSZ) based dual-phase composite system has been investigated in this work. As the dense layer in an oxygen transport membrane device, transport properties profoundly affect the membrane performance. Isotopic Exchange Depth Profile (IEDP) combined with Secondary Ion Mass Spectroscopy (SIMS) was performed to investigate the oxygen ionic transport in the composite materials and the electrical conductivity was measured by the 4-Probe DC method. In order to achieve improved performance, optimisation strategies were also applied, including varying the Cr substitution level in the LSCrF single phase materials and changing the phase ratios in the composite systems. For the electrical conductivity behaviour, in the composite system a percolation threshold was observed at around 20-30 vol% for all Cr:Fe ratios (LSCrF37, LSCrF55 and LSCrF73). Among these three systems, the LSCrF73-based composites presented the highest electrical conductivity. The diffusion measurements were firstly carried out at the macroscopic scale and the ‘effective’ diffusion kinetics were obtained. In a dry oxygen atmosphere, the predominant phase for the surface exchange process was determined to be the LSCrF phase while the ScSZ-based ionic conductor dominated the bulk diffusion. The percolation limit for the diffusion coefficients was observed at a composition of around 30 vol% ionic conductor for the three measured systems (LSCrF37-10Sc1CeSZ, LSCrF55-10Sc1CeSZ, and LSCrF73-10Sc1CeSZ) and the LSCrF73 based dual-phase composites displayed the best bulk diffusivity. Subsequently, in oxygen diffusion studies at the microscopic scale using Focused Ion Beam (FIB)-SIMS, a synergistic effect between the two phases was observed in the composite materials: a decreased surface exchange coefficient (k) was observed for the MIEC phase LSCrF while an enhanced k was obtained for the pure ionic conductor (10Sc1CeSZ) compared to the corresponding isolated single-phase materials. Further mechanism studies were performed on a specialised sample by applying IEDP, SIMS and Low Energy Ion Scattering (LEIS) techniques. The plausible origin of the synergistic effect is suggested to be a combination of the spillover type mechanism and the self-cleaning behaviour of the LSCrF based upon these observations. Prior to the dual-phase composite materials, the starting single-phase materials, LSCrF and ScSZ were firstly characterised. As the Cr substitution increased, the electrical conductivity increased and the maximum value was achieved in the LSCrF73 phase while the bulk diffusivity of the LSCrF decreased. Fast grain boundary diffusion behaviour was observed in the LSCrF73 single phase material. Additionally, the diffusion behaviour of both the single-phase and dual-phase samples in a pure water vapour environment was lastly studied by using labelled H218O to reflect operating atmospheres. The diffusion coefficient (D*) at 800 ̊C of LSCrF was found to increase dramatically by 3 orders of magnitude compared to an isothermal experiment under dry oxygen atmosphere. The surface exchange coefficient of 10Sc1CeSZ has been improved to 1.5×10-6 cm s-1 at 800 ̊C while in dry O2 conditions almost no 18O has been exchanged into the sample. For the LSCrF-ScCeSZ composite, ScCeSZ single phase dominates both the surface exchange process and the bulk diffusion in pure water vapour atmosphere.Open Acces

Determining the Fundamental Failure Modes in Ni-rich Lithium Ion Battery Cathodes

Challenges associated with in-service mechanical degradation of Li-ion battery cathodes has prompted a transition from polycrystalline to single crystal cathode materials. Whilst for single crystal materials, dislocation-assisted crack formation is assumed to be the dominating failure mechanism throughout battery life, there is little direct information about their mechanical behaviour, and mechanistic understanding remains elusive. Here, we demonstrated, using in situ micromechanical testing, direct measurement of local mechanical properties within LiNi0.8Mn0.1Co0.1O2 single crystalline domains. We elucidated the dislocation slip systems, their critical stresses, and how slip facilitate cracking. We then compared single crystal and polycrystal deformation behaviour. Our findings answer two fundamental questions critical to understanding cathode degradation: What dislocation slip systems operate in Ni-rich cathode materials? And how does slip cause fracture? This knowledge unlocks our ability to develop tools for lifetime prediction and failure risk assessment, as well as in designing novel cathode materials with increased toughness in-service

Toward an Understanding of SEI Formation and Lithium Plating on Copper in Anode-Free Batteries.

Funder: Blavatnik Family Foundation"Anode-free" batteries present a significant advantage due to their substantially higher energy density and ease of assembly in a dry air atmosphere. However, issues involving lithium dendrite growth and low cycling Coulombic efficiencies during operation remain to be solved. Solid electrolyte interphase (SEI) formation on Cu and its effect on Li plating are studied here to understand the interplay between the Cu current collector surface chemistry and plated Li morphology. A native interphase layer (N-SEI) on the Cu current collector was observed with solid-state nuclear magnetic resonance spectroscopy (ssNMR) and electrochemical impedance spectroscopy (EIS). Cyclic voltammetry (CV) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) studies showed that the nature of the N-SEI is affected by the copper interface composition. An X-ray photoelectron spectroscopy (XPS) study identified a relationship between the applied voltage and SEI composition. In addition to the typical SEI components, the SEI contains copper oxides (Cu x O) and their reduction reaction products. Parasitic electrochemical reactions were observed via in situ NMR measurements of Li plating efficiency. Scanning electron microscopy (SEM) studies revealed a correlation between the morphology of the plated Li and the SEI homogeneity, current density, and rest time in the electrolyte before plating. Via ToF-SIMS, we found that the preferential plating of Li on Cu is governed by the distribution of ionically conducting rather than electronic conducting compounds. The results together suggest strategies for mitigating dendrite formation by current collector pretreatment and controlled SEI formation during the first battery charge

Understanding improved capacity retention at 4.3 V in modified single crystal Ni-rich NMC//graphite pouch cells at elevated temperature

The capacity retention of commercially-sourced pouch cells with single crystal Al surface-doped Ni-rich cathodes (LiNi0.834Mn0.095Co0.071O2) is examined. The degradation-induced capacity fade becomes more pronounced as the upper-cut-off voltage (UCV) increases from 4.2 V to 4.3 V (vs. graphite) at a fixed cycling temperature (either 25 or 40 °C). However, cycles with 4.3 V UCV (slightly below the oxygen loss onset) show better capacity retention upon increasing the cycling temperature from 25 °C to 40 °C. Namely, after 500 cycles at 4.3 V UCV, cycling temperature at 40 °C retains 85.5% of the initial capacity while cycling at 25 °C shows 75.0% capacity retention. By employing a suite of electrochemical, X-ray spectroscopy and secondary ion mass spectrometry techniques, we attribute the temperature-induced improvement of the capacity retention at high UCV to the combined effects of Al surface-dopants, electrochemically resilient single crystal Ni-rich particles, and thermally-improved Li kinetics translating into better electrochemical performance. If cycling remains below the lattice oxygen loss onset, improved capacity retention in industrial cells should be achieved in single crystal Ni-rich cathodes with the appropriate choice of cycling parameter, particle quality, and particle surface dopants

Understanding improved capacity retention at 4.3 V in modified single crystal Ni-rich NMC//graphite pouch cells at elevated temperature

The capacity retention of commercially-sourced pouch cells with single crystal Al surface-doped Ni-rich cathodes (LiNi0.834Mn0.095Co0.071O2) is examined. The degradation-induced capacity fade becomes more pronounced as the upper-cut-off voltage (UCV) increases from 4.2 V to 4.3 V (vs. graphite) at a fixed cycling temperature (either 25 or 40 °C). However, cycles with 4.3 V UCV (slightly below the oxygen loss onset) show better capacity retention upon increasing the cycling temperature from 25 °C to 40 °C. Namely, after 500 cycles at 4.3 V UCV, cycling temperature at 40 °C retains 85.5% of the initial capacity while cycling at 25 °C shows 75.0% capacity retention. By employing a suite of electrochemical, X-ray spectroscopy and secondary ion mass spectrometry techniques, we attribute the temperature-induced improvement of the capacity retention at high UCV to the combined effects of Al surface-dopants, electrochemically resilient single crystal Ni-rich particles, and thermally-improved Li kinetics translating into better electrochemical performance. If cycling remains below the lattice oxygen loss onset, improved capacity retention in industrial cells should be achieved in single crystal Ni-rich cathodes with the appropriate choice of cycling parameter, particle quality, and particle surface dopants

The dynamic evolution of multipoint interplanetary coronal mass ejections observed with BepiColombo, Tianwen-1, and MAVEN

We present two multipoint interplanetary coronal mass ejections (ICMEs) detected by the Tianwen-1 and Mars Atmosphere and Volatile Evolution spacecraft at Mars and the BepiColombo (0.56 au ∼0.67 au) upstream of Mars from 2021 December 5 to 31. This is the first time that BepiColombo is used as an upstream solar wind monitor ahead of Mars and that Tianwen-1 is used to investigate the magnetic field characteristics of ICMEs at Mars. The Heliospheric Upwind Extrapolation time model was used to connect the multiple in situ observations and the coronagraph observations from STEREO/SECCHI and SOHO/LASCO. The first fast coronal mass ejection event (∼761.2 km s−1), which erupted on December 4, impacted Mars centrally and grazed BepiColombo by its western flank. The ambient slow solar wind decelerated the west flank of the ICME, implying that the ICME event was significantly distorted by the solar wind structure. The second slow ICME event (∼390.7 km s−1) underwent an acceleration from its eruption to a distance within 0.69 au and then traveled with the constant velocity of the ambient solar wind. These findings highlight the importance of background solar wind in determining the interplanetary evolution and global morphology of ICMEs up to Mars distance. Observations from multiple locations are invaluable for space weather studies at Mars and merit more exploration in the future

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data