Interfacial Chemistry in Solid-State Batteries: Formation of Interphase and Its Consequences

Benefiting from extremely high shear modulus and high ionic transference number, solid electrolytes are promising candidates to address both the dendrite-growth and electrolyte-consumption problems inherent to the widely adopted liquid-phase electrolyte batteries. However, solid electrolyte/electrode interfaces present high resistance and complicated morphology, hampering the development of solid-state battery systems, while requiring advanced analysis for rational improvement. Here, we employ an ultrasensitive three-dimensional (3D) chemical analysis to uncover the dynamic formation of interphases at the solid electrolyte/electrode interface. While the formation of interphases widens the electrochemical window, their electronic and ionic conductivities determine the electrochemical performance and have a large influence on dendrite growth. Our results suggest that, contrary to the general understanding, highly stable solid electrolytes with metal anodes in fact promote fast dendritic formation, as a result of less Li consumption and much larger curvature of dendrite tips that leads to an enhanced electric driving force. Detailed thermodynamic analysis shows an interphase with low electronic conductivity, high ionic conductivity, and chemical stability, yet having a dynamic thickness and uniform coverage is needed to prevent dendrite growth. This work provides a paradigm for interphase design to address the dendrite challenge, paving the way for the development of robust, fully operational solid-state batteries

Interfacial Chemistry in Solid-State Batteries: Formation of Interphase and Its Consequences

Benefiting from extremely high shear modulus and high ionic transference number, solid electrolytes are promising candidates to address both the dendrite-growth and electrolyte-consumption problems inherent to the widely adopted liquid-phase electrolyte batteries. However, solid electrolyte/electrode interfaces present high resistance and complicated morphology, hampering the development of solid-state battery systems, while requiring advanced analysis for rational improvement. Here, we employ an ultrasensitive three-dimensional (3D) chemical analysis to uncover the dynamic formation of interphases at the solid electrolyte/electrode interface. While the formation of interphases widens the electrochemical window, their electronic and ionic conductivities determine the electrochemical performance and have a large influence on dendrite growth. Our results suggest that, contrary to the general understanding, highly stable solid electrolytes with metal anodes in fact promote fast dendritic formation, as a result of less Li consumption and much larger curvature of dendrite tips that leads to an enhanced electric driving force. Detailed thermodynamic analysis shows an interphase with low electronic conductivity, high ionic conductivity, and chemical stability, yet having a dynamic thickness and uniform coverage is needed to prevent dendrite growth. This work provides a paradigm for interphase design to address the dendrite challenge, paving the way for the development of robust, fully operational solid-state batteries

Formation and Inhibition of Metallic Lithium Microstructures in Lithium Batteries Driven by Chemical Crossover

The formation of metallic lithium microstructures in the form of dendrites or mosses at the surface of anode electrodes (<i>e</i>.<i>g</i>., lithium metal, graphite, and silicon) leads to rapid capacity fade and poses grave safety risks in rechargeable lithium batteries. We present here a direct, relative quantitative analysis of lithium deposition on graphite anodes in pouch cells under normal operating conditions, paired with a model cathode material, the layered nickel-rich oxide LiNi_0.61Co_0.12Mn_0.27O₂, over the course of 3000 charge–discharge cycles. Secondary-ion mass spectrometry chemically dissects the solid–electrolyte interphase (SEI) on extensively cycled graphite with virtually atomic depth resolution and reveals substantial growth of Li-metal deposits. With the absence of apparent kinetic (<i>e</i>.<i>g</i>., fast charging) or stoichiometric restraints (<i>e</i>.<i>g</i>., overcharge) during cycling, we show lithium deposition on graphite is triggered by certain transition-metal ions (manganese in particular) dissolved from the cathode in a disrupted SEI. This insidious effect is found to initiate at a very early stage of cell operation (<200 cycles) and can be effectively inhibited by substituting a small amount of aluminum (∼1 mol %) in the cathode, resulting in much reduced transition-metal dissolution and drastically improved cyclability. Our results may also be applicable to studying the unstable electrodeposition of lithium on other substrates, including Li metal

Revealing the Chemistry and Morphology of Buried Donor/Acceptor Interfaces in Organic Photovoltaics

With power conversion efficiencies (PCEs) of <13% and plagued by stability issues, organic photovoltaics (OPVs) still lack wide adoption, despite significant recent advances. Currently, the most progress in OPV device performance is achieved by “trial-and-error” preparation procedures that lead to complex and largely unknowndespite tremendous analytical effortsmorphologies. Here, we demonstrate a proof-of-principle, chemical imaging methodology that combines experimental high spatial sensitivity and chemical selectivity with theoretical modeling, capable of analyzing the three-dimensional composition and morphology of virtually any device. Allowing the precise measurement of composition and direct visualization of film morphology with depth, our approach reveals the intricate buried donor/acceptor (D/A) interface of a model polymer/fullerene system, poly­(3-hexylthiphene-2,5-diyl)/[6,6]-phenyl-C₆₁-butyric acid methyl ester (P3HT/PCBM). In particular, our technique is able to identify and quantify the D/A interface length, that is, the extent of molecular mixing at the D/A interface, a parameter crucial for device performance, yet never measured. Extracting this parameter allows demonstrating that, contrary to the general understanding, when starting with a fully mixed D/A phase in our model system, thermal annealing, which is known to substantially (however limited) increase the device performance by phase segregation, does not create but small amounts of pure phases, leaving the device mostly mixed, which limits the performance improvement

Character descriptions

Descriptions of characters from the phylogenetic analysi

Gabbott_et_al_2016_mtx

Data matrix in NEXUS forma

Pigmented anatomy in Carboniferous cyclostomes and the evolution of the vertebrate eye

The success of vertebrates is linked to the evolution of a camera-style eye and sophisticated visual system. In the absence of useful data from fossils, scenarios for evolutionary assembly of the vertebrate eye have been based necessarily on evidence from development, molecular genetics and comparative anatomy in living vertebrates. Unfortunately, steps in the transition from a light-sensitive 'eye spot' in invertebrate chordates to an image-forming camera-style eye in jawed vertebrates are constrained only by hagfish and lampreys (cyclostomes), which are interpreted to reflect either an intermediate or degenerate condition. Here, we report-based on evidence of size, shape, preservation mode and localized occurrence-the presence of melanosomes (pigment-bearing organelles) in fossil cyclostome eyes. Time of flight secondary ion mass spectrometry analyses reveal secondary ions with a relative intensity characteristic of melanin as revealed through principal components analyses. Our data support the hypotheses that extant hagfish eyes are degenerate, not rudimentary, that cyclostomes are monophyletic, and that the ancestral vertebrate had a functional visual system. We also demonstrate integument pigmentation in fossil lampreys, opening up the exciting possibility of investigating colour patterning in Palaeozoic vertebrates. The examples we report add to the record of melanosome preservation in Carboniferous fossils and attest to surprising durability of melanosomes and biomolecular melanin

Direct Observation of Poly(Methyl Methacrylate) Removal from a Graphene Surface

Poly­(methyl methacrylate) (PMMA) is commonly used as a temporary support layer for chemical vapor deposition (CVD) graphene transfer; it is then removed by a chemical or thermal treatment. Regardless of the method used for PMMA removal, polymer residues are left on the graphene surface, which alter its intrinsic properties. A method based on isotope labeling of PMMA and time-of-flight secondary ion mass spectrometry (ToF-SIMS) has now been developed to identify, locate, and quantify these residues. It is shown that vacuum annealing does not completely remove the PMMA residues but, instead, transforms them into amorphous carbon. In contrast, air annealing under optimized conditions generates a PMMA-free surface with limited damage to the graphene structure. This cleaned graphene surface demonstrates low friction which is comparable with that of pristine graphene film

In Situ Optical Imaging of Sodium Electrodeposition: Effects of Fluoroethylene Carbonate

The morphologies of sodium electrodeposits and gas evolution were studied in a system comprising a symmetrical Na/Na optical cell, a digital microscope, and an electrochemical workstation. Sodium deposition in ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) generated large volumes of gas and fragile, porous dendrites. The use of fluoroethylene carbonate (FEC) greatly reduced gassing during deposition and demonstrated superior cycling performance, impedance, and cycling efficiency when it was used as a cosolvent with DEC (1:1 vol); however, porous depositions persisted. Time of flight secondary-ion mass spectrometry revealed that the solid-electrolyte interphase formed in FEC/DEC, in contrast with the EC/DEC electrolyte, is thicker, richer in NaF, and forms a less dense polymer organic layer

Understanding the Interface Dipole of Copper Phthalocyanine (CuPc)/C₆₀: Theory and Experiment

Interface dipole determines the electronic energy alignment in donor/acceptor interfaces and plays an important role in organic photovoltaics. Here we present a study combining first principles density functional theory (DFT) with ultraviolet photoemission spectroscopy (UPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) to investigate the interface dipole, energy level alignment, and structural properties at the interface between CuPc and C₆₀. DFT finds a sizable interface dipole for the face-on orientation, in quantitative agreement with the UPS measurement, and rules out charge transfer as the origin of the interface dipole. Using TOF-SIMS, we show that the interfacial morphology for the bilayer CuPc/C₆₀ film is characterized by molecular intermixing, containing both the face-on and the edge-on orientation. The complementary experimental and theoretical results provide both insight into the origin of the interface dipole and direct evidence for the effect of interfacial morphology on the interface dipole