Operando optical tracking of single-particle ion dynamics in batteries.

The key to advancing lithium-ion battery technology-in particular, fast charging-is the ability to follow and understand the dynamic processes occurring in functioning materials under realistic conditions, in real time and on the nano- to mesoscale. Imaging of lithium-ion dynamics during battery operation (operando imaging) at present requires sophisticated synchrotron X-ray1-7 or electron microscopy8,9 techniques, which do not lend themselves to high-throughput material screening. This limits rapid and rational materials improvements. Here we introduce a simple laboratory-based, optical interferometric scattering microscope10-13 to resolve nanoscopic lithium-ion dynamics in battery materials, and apply it to follow cycling of individual particles of the archetypal cathode material14,15, LixCoO2, within an electrode matrix. We visualize the insulator-to-metal, solid solution and lithium ordering phase transitions directly and determine rates of lithium diffusion at the single-particle level, identifying different mechanisms on charge and discharge. Finally, we capture the dynamic formation of domain boundaries between different crystal orientations associated with the monoclinic lattice distortion at the Li0.5CoO2 composition16. The high-throughput nature of our methodology allows many particles to be sampled across the entire electrode and in future will enable exploration of the role of dislocations, morphologies and cycling rate on battery degradation. The generality of our imaging concept means that it can be applied to study any battery electrode, and more broadly, systems where the transport of ions is associated with electronic or structural changes. Such systems include nanoionic films, ionic conducting polymers, photocatalytic materials and memristors.

Li iontronics in single-crystalline T-Nb2O5 thin films with vertical ionic transport channels.

The niobium oxide polymorph T-Nb2O5 has been extensively investigated in its bulk form especially for applications in fast-charging batteries and electrochemical (pseudo)capacitors. Its crystal structure, which has two-dimensional (2D) layers with very low steric hindrance, allows for fast Li-ion migration. However, since its discovery in 1941, the growth of single-crystalline thin films and its electronic applications have not yet been realized, probably due to its large orthorhombic unit cell along with the existence of many polymorphs. Here we demonstrate the epitaxial growth of single-crystalline T-Nb2O5 thin films, critically with the ionic transport channels oriented perpendicular to the film's surface. These vertical 2D channels enable fast Li-ion migration, which we show gives rise to a colossal insulator-metal transition, where the resistivity drops by 11 orders of magnitude due to the population of the initially empty Nb 4d0 states by electrons. Moreover, we reveal multiple unexplored phase transitions with distinct crystal and electronic structures over a wide range of Li-ion concentrations by comprehensive in situ experiments and theoretical calculations, which allow for the reversible and repeatable manipulation of these phases and their distinct electronic properties. This work paves the way for the exploration of novel thin films with ionic channels and their potential applications.

Operando monitoring of single-particle kinetic state-of-charge heterogeneities and cracking in high-rate Li-ion anodes.

To rationalize and improve the performance of newly developed high-rate battery electrode materials, it is crucial to understand the ion intercalation and degradation mechanisms occurring during realistic battery operation. Here we apply a laboratory-based operando optical scattering microscopy method to study micrometre-sized rod-like particles of the anode material Nb14W3O44 during high-rate cycling. We directly visualize elongation of the particles, which, by comparison with ensemble X-ray diffraction, allows us to determine changes in the state of charge of individual particles. A continuous change in scattering intensity with state of charge enables the observation of non-equilibrium kinetic phase separations within individual particles. Phase field modelling (informed by pulsed-field-gradient nuclear magnetic resonance and electrochemical experiments) supports the kinetic origin of this separation, which arises from the state-of-charge dependence of the Li-ion diffusion coefficient. The non-equilibrium phase separations lead to particle cracking at high rates of delithiation, particularly in longer particles, with some of the resulting fragments becoming electrically disconnected on subsequent cycling. These results demonstrate the power of optical scattering microscopy to track rapid non-equilibrium processes that would be inaccessible with established characterization techniques.

Clonal haematopoiesis of indeterminate potential in patients with venous thromboembolism.

Over the last decade, the concept of Clonal haematopoiesis of undetermined potential (CHIP) has emerged. Low frequency somatic mutations in hematopoietic cells can occur with age and might allow formation of clones in individuals with no characterized haematological pathology. These CHIP mutations are associated with an increased risk of cancer or atherothrombosis, and their prevalence are more and more studied in pathologies with an inflammatory component. In our study, we analysed, by next generation sequencing, the prevalence of CHIP mutation in 94 patients with deep venous thrombosis (DVT), distinguishing two clinical phenotypes: provoked distal and non-provoked proximal DVTs. We show that there is no difference in CHIP prevalence between these two groups, nor with a matched-aged control group. The number of mutation per patients and the affected genes remain also the same between the three groups. Consequently and despite the relative small number of patients in each cohort, it seems that CHIP is not a strong concern in venous thromboembolism.

Charge Transfer Band Gap as an Indicator of Hysteresis in Li-Disordered Rock Salt Cathodes for Li-Ion Batteries.

Disordered rock salt cathodes showing both anionic and cationic redox are being extensively studied for their very high energy storage capacity. Mn-based disordered rock salt compounds show much higher energy efficiency compared to the Ni-based materials as a result of the different voltage hysteresis, 0.5 and 2 V, respectively. To understand the origin of this difference, we herein report the design of two model compounds, Li1.3Ni0.27Ta0.43O2 and Li1.3Mn0.4Ta0.3O2, and study their charge compensation mechanism through the uptake and removal of Li via an arsenal of analytical techniques. We show that the different voltage hysteresis with Ni or Mn substitution is due to the different reduction potential for anionic redox. We rationalized such a finding by DFT calculations and propose this phenomenon to be nested in the smaller charge transfer band gap of the Ni-based compounds compared to that of the Mn ones. Altogether, these findings provide vital guidelines for designing high-capacity disordered rock salt cathode materials based on anionic redox activity for the next generation of Li ion batteries.

Time-Dependent Probability Density Functions and Attractor Structure in Self-Organised Shear Flows.

We report the time-evolution of Probability Density Functions (PDFs) in a toy model of self-organised shear flows, where the formation of shear flows is induced by a finite memory time of a stochastic forcing, manifested by the emergence of a bimodal PDF with the two peaks representing non-zero mean values of a shear flow. Using theoretical analyses of limiting cases, as well as numerical solutions of the full Fokker-Planck equation, we present a thorough parameter study of PDFs for different values of the correlation time and amplitude of stochastic forcing. From time-dependent PDFs, we calculate the information length ( L ), which is the total number of statistically different states that a system passes through in time and utilise it to understand the information geometry associated with the formation of bimodal or unimodal PDFs. We identify the difference between the relaxation and build-up of the shear gradient in view of information change and discuss the total information length ( L ∞ = L ( t → ∞ ) ) which maps out the underlying attractor structures, highlighting a unique property of L ∞ which depends on the trajectory/history of a PDF's evolution.

Multi-scale characterization of lead-rich deposited particles originating from the fire of Notre-Dame de Paris.

Fire is a major hazard for built heritage. The fire at Notre-Dame on April 15, 2019 completely destroyed the woodframe and the lead roof (about 285 tons) almost entirely melted due to high temperatures. A part of the molten lead escaped into the atmosphere in the form of aerosols while the majority remains within cathedral enclosure in the form of deposits, metallic remains, spatters etc. In particular unusual yellowish deposits of lead-rich particles were observed and collected inside the monument (in the nave, near the organ and in St-Eloi Chapel). These were then thoroughly characterized to identify the neoformed lead compounds. Both bulk and local analyses were carried out to obtain particle morphology and size distribution, chemistry and mineralogy of the deposits, from macro to nanoscale. We found that the fire-related deposits all contain high amount of lead (10 to 44 %) mainly in the form of monoxides (litharge and massicot) with other lead-bearing phases (Ca-plumbate, metallic lead, lead sulfates and carbonates, plattnerite) in smaller amount. These lead phases are concentrated in heterogeneous microspheres, at the periphery of terrigenous minerals (calcite, quartz, feldspars) or mixed with anhydrite minerals. The size distribution shows that the fire produced giant particles (> 100 µm in diameter) similar to those found near the fallout from industrial emissions. This study provides a better understanding of the lead contamination pathways following the Notre-Dame cathedral fire and new insights into the reactivity of lead during a fire.

Higher energy and safer sodium ion batteries via an electrochemically made disordered Na3V2(PO4)2F3 material.

The growing need to store an increasing amount of renewable energy in a sustainable way has rekindled interest for sodium-ion battery technology, owing to the natural abundance of sodium. Presently, sodium-ion batteries based on Na3V2(PO4)2F3/C are the subject of intense research focused on improving the energy density by harnessing the third sodium, which has so far been reported to be electrochemically inaccessible. Here, we are able to trigger the activity of the third sodium electrochemically via the formation of a disordered NaxV2(PO4)2F3 phase of tetragonal symmetry (I4/mmm space group). This phase can reversibly uptake 3 sodium ions per formula unit over the 1 to 4.8 V voltage range, with the last one being re-inserted at 1.6 V vs Na+/Na0. We track the sodium-driven structural/charge compensation mechanism associated to the new phase and find that it remains disordered on cycling while its average vanadium oxidation state varies from 3 to 4.5. Full sodium-ion cells based on this phase as positive electrode and carbon as negative electrode show a 10-20% increase in the overall energy density.