Lithium-rich layered transition metal oxide positive electrodes offer access to anion redox at high potentials, thereby promising high energy densities for lithium-ion batteries. However, anion redox is also associated with several unfavorable electrochemical properties, such as open-circuit voltage hysteresis. Here we reveal that in Li1.17–xNi0.21Co0.08Mn0.54O2, these properties arise from a strong coupling between anion redox and cation migration. We combine various X-ray spectroscopic, microscopic, and structural probes to show that partially reversible transition metal migration decreases the potential of the bulk oxygen redox couple by > 1 V, leading to a reordering in the anionic and cationic redox potentials during cycling. First principles calculations show that this is due to the drastic change in the local oxygen coordination environments associated with the transition metal migration. We propose that this mechanism is involved in stabilizing the oxygen redox couple, which we observe spectroscopically to persist for 500 charge/discharge cycles.

Neuromorphic computers could overcome efficiency bottlenecks inherent to conventional computing through parallel programming and readout of artificial neural network weights in a crossbar memory array. However, selective and linear weight updates and <10-nanoampere read currents are required for learning that surpasses conventional computing efficiency. We introduce an ionic floating-gate memory array based on a polymer redox transistor connected to a conductive-bridge memory (CBM). Selective and linear programming of a redox transistor array is executed in parallel by overcoming the bridging threshold voltage of the CBMs. Synaptic weight readout with currents <10 nanoamperes is achieved by diluting the conductive polymer with an insulator to decrease the conductance. The redox transistors endure >1 billion write-read operations and support >1-megahertz write-read frequencies.

Abstract:The kinetics and uniformity of ion insertion reactions at the solid/liquid interface govern the rate capability and lifetime, respectively, of electrochemical devices such as Li-ion batteries.We develop an operando X-ray microscopy platform that maps the dynamics of the Li composition and insertion rate in LiXFePO4, and show that nanoscale spatial variations in rate and in composition control the lithiation pathway at the sub-particle length scale. Specifically, spatial variations in the insertion rate constant lead to the formation of nonuniform domains, and the composition dependence of the rate constant amplifies nonuniformities during delithiation but suppresses them during lithiation, and moreover stabilizes the solid solution during lithiation. This coupling of lithium composition and surface reaction rates controls the kinetics and uniformity during electrochemical ion insertion.One Sentence Summary: X-ray microscopy reveals the nanoscale evolution of composition and reaction rate inside a Li-ion battery during cycling Main Text: The insertion of a guest ion into the host crystal is the fundamental reaction underpinning insertion electrochemistry and has been applied to store energy (1), tune catalysts (2), and switch optoelectronic properties (3). In Li-ion batteries, for example, Li ions from the 2 liquid electrolyte insert into solid host particles in the electrode. Nanoscale intraparticle electrochemical inhomogeneities in phase and in composition are responsible for mechanical strain and fracture which decrease the reversibility of the reaction (4). Moreover, these nonuniformities make it difficult to correlate current-voltage measurements to microscopic ion insertion mechanisms. Simultaneously quantifying nonuniform nanoscale reaction kinetics and the underlying material composition at the solid-liquid interface holds the key to improving device performance.A gold standard material for investigating ion insertion reactions is LiXFePO4 (0

Many battery electrodes contain ensembles of nanoparticles that phase-separate upon (de)intercalation. In such electrodes, the fraction of actively-intercalating particles directly impacts cycle life: a vanishing population concentrates the current in a small number of particles, leading to current hotspots. Reports on the active particle population in the phase-separating electrode lithium iron phosphate (LFP) vary widely, ranging from around 0% (particle-byparticle) to 100% (concurrent intercalation). Using synchrotron-based X-ray microscopy, we probed the individual state-of-charge for over 3,000 LFP particles. We observed that the active population depends strongly on the cycling current, exhibiting particle-by-particle-like behaviour at low rates and increasingly concurrent behaviour at high rates, consistent with our phase-field porous electrode simulations. Contrary to intuition, the current density, or current per active internal surface area, is nearly invariant with the global electrode cycling rate. Rather, the electrode accommodates higher current by increasing the active particle population. This behaviour results from thermodynamic transformation barriers in LFP, and such a phenomenon likely extends to other phase-separating battery materials. We propose that modifying the transformation barrier and exchange current density can increase the active population and thus the current homogeneity. This could introduce new paradigms to enhance the cycle life of phaseseparating battery electrodes. 3Electrochemical systems can provide clean and efficient routes for energy conversion and storage. Many electrochemical devices such as batteries, fuel cells, and supercapacitors consist of porous electrodes containing ensembles of nanoparticles 1 . For typical microstructures, the particle density can reach as high as 10 15 cm -3 . To further increase complexity, many intercalation battery electrodes, such as graphite 2 , lithium iron phosphate 3,4 , lithium titanate 5 , and spinel lithium nickel manganese oxide 6 , phase-separate upon (de)intercalation. Such electrodes are physically and chemically heterogeneous on the nanoscale, and likely exhibit inhomogeneous current distributions.In phase-separating electrodes, the active particle population is a crucial factor in determining the overall electrode current and the degree of current homogeneity. The electrode current is given by:where is the reaction area of the th actively-intercalating particle, and is the current density of that particle. Under the approximation of similar particle size, we obtain the final expression in equation 1, where ̅ is the average current density of all actively-intercalating particles, is the total internal surface area of all particles (rather than the projected electrode area), and is the so-called active population. When approaches 0%, the electrode intercalates particle-by-particle with a heterogeneous current distribution; when approaches 100%, the electrode intercalates concurrently with a more homogeneous current ...

Exosomes play an important role in numerous cellular processes. Fundamental study and practical use of exosomes are significantly constrained by the lack of analytical tools capable of physical and biochemical characterization. In this paper, we present an optical approach capable of imaging single exosomes in a label-free manner, using interferometric plasmonic microscopy. We demonstrate monitoring of the real-time adsorption of exosomes onto a chemically modified Au surface, calculating the image intensity, and determining the size distribution. The sizing capability enables us to quantitatively measure the membrane fusion activity between exosomes and liposomes. We also report the recording of the dynamic interaction between exosomes and antibodies at the single-exosome level, and the tracking of hit-stay-run behavior of exosomes on an antibody-coated surface. We anticipate that the proposed method will contribute to clinical exosome analysis and to the exploration of fundamental issues such as the exosome–antibody binding kinetics.