Fast Diagnosis of Failure Mechanisms and Lifetime Prediction of Li Metal Batteries.

Lithium (Li) metal serving as an anode has the potential to double or triple stored energies in rechargeable Li batteries. However, they typically have short cycling lifetimes due to parasitic reactions between the Li metal and electrolyte. It is critically required to develop early fault-detection methods for different failure mechanisms and quick lifetime-prediction methods to ensure rapid development. Prior efforts to determine the dominant failure mechanisms have typically required destructive cell disassembly. In this study, non-destructive diagnostic method based on rest voltages and coulombic efficiency are used to easily distinguish the different failure mechanisms-from loss of Li inventory, electrolyte depletion, and increased cell impedance-which are deeply understood and well validated by experiments and modeling. Using this new diagnostic method, the maximum lifetime of a Li metal cell can be quickly predicted from tests of corresponding anode-free cells, which is important for the screenings of electrolytes, anode stabilization, optimization of operating conditions, and rational battery design.

Interfaces and Interphases in All-Solid-State Batteries with Inorganic Solid Electrolytes.

All-solid-state batteries (ASSBs) have attracted enormous attention as one of the critical future technologies for safe and high energy batteries. With the emergence of several highly conductive solid electrolytes in recent years, the bottleneck is no longer Li-ion diffusion within the electrolyte. Instead, many ASSBs are limited by their low Coulombic efficiency, poor power performance, and short cycling life due to the high resistance at the interfaces within ASSBs. Because of the diverse chemical/physical/mechanical properties of various solid components in ASSBs as well as the nature of solid-solid contact, many types of interfaces are present in ASSBs. These include loose physical contact, grain boundaries, and chemical and electrochemical reactions to name a few. All of these contribute to increasing resistance at the interface. Here, we present the distinctive features of the typical interfaces and interphases in ASSBs and summarize the recent work on identifying, probing, understanding, and engineering them. We highlight the complicated, but important, characteristics of interphases, namely the composition, distribution, and electronic and ionic properties of the cathode-electrolyte and electrolyte-anode interfaces; understanding these properties is the key to designing a stable interface. In addition, conformal coatings to prevent side reactions and their selection criteria are reviewed. We emphasize the significant role of the mechanical behavior of the interfaces as well as the mechanical properties of all ASSB components, especially when the soft Li metal anode is used under constant stack pressure. Finally, we provide full-scale (energy, spatial, and temporal) characterization methods to explore, diagnose, and understand the dynamic and buried interfaces and interphases. Thorough and in-depth understanding on the complex interfaces and interphases is essential to make a practical high-energy ASSB.

Tuning Internal Strain in Metal-Organic Frameworks via Vapor Phase Infiltration for CO2 Reduction.

A gas-phase approach to form Zn coordination sites on metal-organic frameworks (MOFs) by vapor-phase infiltration (VPI) was developed. Compared to Zn sites synthesized by the solution-phase method, VPI samples revealed approximately 2.8 % internal strain. Faradaic efficiency towards conversion of CO2 to CO was enhanced by up to a factor of four, and the initial potential was positively shifted by 200-300 mV. Using element-specific X-ray absorption spectroscopy, the local coordination environment of the Zn center was determined to have square-pyramidal geometry with four Zn-N bonds in the equatorial plane and one Zn-OH2 bond in the axial plane. The fine-tuned internal strain was further supported by monitoring changes in XRD and UV/Visible absorption spectra across a range of infiltration cycles. The ability to use internal strain to increase catalytic activity of MOFs suggests that applying this strategy will enhance intrinsic catalytic capabilities of a variety of porous materials.

Quantifying inactive lithium in lithium metal batteries.

Lithium metal anodes offer high theoretical capacities (3,860 milliampere-hours per gram)1, but rechargeable batteries built with such anodes suffer from dendrite growth and low Coulombic efficiency (the ratio of charge output to charge input), preventing their commercial adoption2,3. The formation of inactive ('dead') lithium- which consists of both (electro)chemically formed Li+ compounds in the solid electrolyte interphase and electrically isolated unreacted metallic Li0 (refs 4,5)-causes capacity loss and safety hazards. Quantitatively distinguishing between Li+ in components of the solid electrolyte interphase and unreacted metallic Li0 has not been possible, owing to the lack of effective diagnostic tools. Optical microscopy6, in situ environmental transmission electron microscopy7,8, X-ray microtomography9 and magnetic resonance imaging10 provide a morphological perspective with little chemical information. Nuclear magnetic resonance11, X-ray photoelectron spectroscopy12 and cryogenic transmission electron microscopy13,14 can distinguish between Li+ in the solid electrolyte interphase and metallic Li0, but their detection ranges are limited to surfaces or local regions. Here we establish the analytical method of titration gas chromatography to quantify the contribution of unreacted metallic Li0 to the total amount of inactive lithium. We identify the unreacted metallic Li0, not the (electro)chemically formed Li+ in the solid electrolyte interphase, as the dominant source of inactive lithium and capacity loss. By coupling the unreacted metallic Li0 content to observations of its local microstructure and nanostructure by cryogenic electron microscopy (both scanning and transmission), we also establish the formation mechanism of inactive lithium in different types of electrolytes and determine the underlying cause of low Coulombic efficiency in plating and stripping (the charge and discharge processes, respectively, in a full cell) of lithium metal anodes. We propose strategies for making lithium plating and stripping more efficient so that lithium metal anodes can be used for next-generation high-energy batteries.

Extending the limits of powder diffraction analysis: Diffraction parameter space, occupancy defects, and atomic form factors.

Although the determination of site occupancies is often a major goal in Rietveld refinement studies, the accurate refinement of site occupancies is exceptionally challenging due to many correlations and systematic errors that have a hidden impact on the final refined occupancy parameters. Through the comparison of results independently obtained from neutron and synchrotron powder diffraction, improved approaches capable of detecting occupancy defects with an exceptional sensitivity of 0.1% (absolute) in the class of layered NMC (Li[NixMnyCoz]O2) Li-ion battery cathode materials have been developed. A new method of visualizing the diffraction parameter space associated with crystallographic site scattering power through the use of f* diagrams is described, and this method is broadly applicable to ternary compounds. The f* diagrams allow the global minimum fit to be easily identified and also permit a robust determination of the number and types of occupancy defects within a structure. Through a comparison of neutron and X-ray diffraction results, a systematic error in the synchrotron results was identified using f* diagrams for a series of NMC compounds. Using neutron diffraction data as a reference, this error was shown to specifically result from problems associated with the neutral oxygen X-ray atomic form factor and could be eliminated by using the ionic O2- form factor for this anion while retaining the neutral form factors for cationic species. The f* diagram method offers a new opportunity to experimentally assess the quality of atomic form factors through powder diffraction studies on chemically related multi-component compounds.

Bioinspired Chemical Communication between Synthetic Nanomotors.

While chemical communication plays a key role in diverse natural processes, the intelligent chemical communication between synthetic nanomotors remains unexplored. The design and operation of bioinspired synthetic nanomotors is presented. Chemical communication between nanomotors is possible and has an influence on propulsion behavior. A chemical "message" is sent from a moving activator motor to a nearby activated (receiver) motor by release of Ag+ ions from a Janus polystyrene/Ni/Au/Ag activator motor to the activated Janus SiO2 /Pt nanomotor. The transmitted silver signal is translated rapidly into a dramatic speed change associated with the enhanced catalytic activity of activated motors. Selective and successive activation of multiple nanomotors is achieved by sequential localized chemical communications. The concept of establishing chemical communication between different synthetic nanomotors paves the way to intelligent nanoscale robotic systems that are capable of cooperating with each other.