Optimized atomic layer deposition of homogeneous, conductive Al2O3 coatings for high-nickel NCM containing ready-to-use electrodes

Atomic layer deposition (ALD) derived ultrathin conformal Al₂O₃ coating has been identified as an effective strategy for enhancing the electrochemical performance of Ni-rich LiNi_xCo_yMn_zO₂ (NCM; 0 ≤x, y, z < 1) based cathode active materials (CAM) in Li-ion batteries. However, there is still a need to better understand the beneficial effect of ALD derived surface coatings on the performance of NCM based composite cathodes. In this work, we applied and optimized a low-temperature ALD derived Al₂O₃ coating on a series of Ni-rich NCM-based (NCM622, NCM71.51.5 and NCM811) ready-to-use composite cathodes and investigated the effect of coating on the surface conductivity of the electrode as well as its electrochemical performance. A highly uniform and conformal coating was successfully achieved on all three different cathode compositions under the same ALD deposition conditions. All the coated cathodes were found to exhibit an improved electrochemical performance during long-term cycling under moderate cycling conditions. The improvement in the electrochemical performance after Al₂O₃ coating is attributed to the suppression of parasitic side reactions between the electrode and the electrolyte during cycling. Furthermore, conductive atomic force microscopy (C-AFM) was performed on the electrode surface as a non-destructive technique to determine the difference in surface morphology and conductivity between uncoated and coated electrodes before and after cycling. C-AFM measurements on pristine cathodes before cycling allow clear separation between the conductive carbon additives and the embedded NCM secondary particles, which show an electrically insulating behavior. More importantly, the measurements reveal that the ALD-derived Al₂O₃ coating with an optimized thickness is thin enough to retain the original conduction properties of the coated electrodes, while thicker coating layers are insulating resulting in a worse cycling performance. After cycling, the surface conductivity of the coated electrodes is maintained, while in the case of uncoated electrodes the surface conductivity is completely suppressed confirming the formation of an insulating cathode electrolyte interface due to the parasitic side reactions. The results not only show the possibilities of C-AFM as a non-destructive evaluation of the surface properties, but also reveal that an optimized coating, which preserves the conductive properties of the electrode surface, is a crucial factor for stabilising the long-term battery performance.

A Rapid and Facile Approach for the Recycling of High-Performance LiNi1-x-y Cox Mny O2 Active Materials

The demand for lithium-ion batteries has risen dramatically over the years. Unfortunately, many of the essential component materials, such as cobalt and lithium, are both costly and of limited abundance. For this reason, the recycling of lithium-ion battery electrodes is crucial to ensuring the availability of such resources and protecting the environment. Herein, a simple and scalable recycling process was developed for the prototypical cathode active material Li_1.02 (Ni_0.8 Co_0.1 Mn_0.1 )_0.98 O₂ (NCM-811). By a combination of thermal decomposition and dissolution steps, spent NCM could be converted into Li₂ CO₃ and a transition metal oxalate blend, which served as precursors for new NCM. Importantly, it was also possible to individually separate each transition metal during the recycling process, thereby extending the utility of this method to a wide variety of NCM compositions. Each intermediate in the process was investigated by scanning electron microscopy and X-ray diffraction. Additionally, the elemental composition of the recycled NCM-811 was confirmed using inductively coupled plasma optical emission spectroscopy and energy-dispersive X-ray spectroscopy. The electrochemical performance of the recycled NCM-811 exhibited up to 80 % of the initial capacity of pristine NCM-811. The method presented herein serves as an efficient and environmentally benign alternative to existing recycling methods for lithium-ion battery electrode materials.

Evidence for a Solid-Electrolyte Inductive Effect in the Superionic Conductor Li10Ge1-xSnxP2S12

Strategies to enhance ionic conductivities in solid electrolytes typically focus on the effects of modifying their crystal structures or of tuning mobile-ion stoichiometries. A less-explored approach is to modulate the chemical bonding interactions within a material to promote fast lithium-ion diffusion. Recently, the idea of a solid-electrolyte inductive effect has been proposed, whereby changes in bonding within the solid-electrolyte host framework modify the potential energy landscape for the mobile ions, resulting in an enhanced ionic conductivity. Direct evidence for a solid-electrolyte inductive effect, however, is lacking-in part because of the challenge of quantifying changes in local bonding interactions within a solid-electrolyte host framework. Here, we consider the evidence for a solid-electrolyte inductive effect in the archetypal superionic lithium-ion conductor Li10Ge1-xSnxP2S12. Substituting Ge for Sn weakens the {Ge,Sn}-S bonding interactions and increases the charge density associated with the S2- ions. This charge redistribution modifies the Li+ substructure causing Li+ ions to bind more strongly to the host framework S2- anions, which in turn modulates the Li+ ion potential energy surface, increasing local barriers for Li+ ion diffusion. Each of these effects is consistent with the predictions of the solid-electrolyte inductive effect model. Density functional theory calculations predict that this inductive effect occurs even in the absence of changes to the host framework geometry due to Ge → Sn substitution. These results provide direct evidence in support of a measurable solid-electrolyte inductive effect and demonstrate its application as a practical strategy for tuning ionic conductivities in superionic lithium-ion conductors.

Enhancing the Electrochemical Performance of LiNi0.70Co0.15Mn0.15O2 Cathodes Using a Practical Solution-Based Al2O3 Coating

Ni-rich Li[Ni_xCo_yMn_1-x-y]O₂ (NCM) cathode materials have attracted great research interest owing to their high energy density and relatively low cost. However, capacity fading because of parasitic side reactions, mainly occurring at the interface with the electrolyte, still hinders widespread application in advanced Li-ion batteries (LIBs). Surface modification via coating is a feasible approach to tackle this issue. Nevertheless, achieving uniform coatings is challenging, especially when using wet chemistry methods. In this work, a protective alumina shell on NCM701515 (70% Ni) was prepared through the reaction of surface-active -OH groups with trimethylaluminum as the precursor. The coated NCM701515 shows significantly improved capacity retention over uncoated (pristine) NCM701515. Part of the reason is the lower impedance buildup during cycling due to the effective suppression of adverse side reactions and secondary particle fracture. Taken together, the solution-based coating strategy described herein offers an easy way to apply surface treatment to stabilize Ni-rich NCM cathode materials in next-generation LIBs.

Local Structure and Influence of Sb Substitution on the Structure-Transport Properties in AgBiSe2

Owing to their intrinsically low thermal conductivity and chemical diversity, materials within the I-V-VI₂ family, and especially AgBiSe₂, have recently attracted interest as promising thermoelectric materials. However, further investigations are needed in order to develop a more fundamental understanding of the origin of the low thermal conductivity in AgBiSe₂, to evaluate possible stereochemical activity of the 6s² lone pair of Bi³⁺, and to further elaborate on chemical design approaches for influencing the occurring phase transitions. In this work, a combination of temperature-dependent X-ray diffraction, Rietveld refinements of laboratory X-ray diffraction data, and pair distribution function analyses of synchrotron X-ray diffraction data is used to tackle the influence of Sb substitution within AgBi_1-xSb_xSe₂ (0 ⩽ x ⩽ 0.15) on the phase transitions, local distortions, and off-centering of the structure. This work shows that, similar to other lone-pair-containing materials, local off-centering and distortions can be found in AgBiSe₂. Furthermore, electronic and thermal transport measurements, in combination with the modeling of point-defect scattering, highlight the importance of structural characterizations toward understanding changes induced by elemental substitutions. This work provides new insights into the structure-transport correlations of the thermoelectric AgBiSe₂.

Ionic Conductivity of the NASICON-Related Thiophosphate Na1+x Ti2-x Gax (PS4 )3

Inspired by the recent interest in fast ionic conducting solids for electrolytes, the ionic conductivity of a novel ionic conductor Na_1+x Ti_2-x Ga_x (PS₄ )₃ has been investigated. Using X-ray diffraction and impedance spectroscopy the sodium ionic conductivity in this compound was demonstrated, in which bond valence sum analysis suggests a tunnel diffusion for Na⁺ . Substitution with Ga³⁺ leads to an increasing Na⁺ content, an expansion of the lattice and an increasing conductivity with increasing x in Na_1+x Ti_2-x Ga_x (PS₄ )₃ . Given the relation to the NASICON family, upon replacement of the phosphate by a thiophosphate group, a rich structural chemistry can be expected in this class of materials. This work demonstrates the potential for making NaTi₂ (PS₄ )₃ an ideal system to study structure-property relationships in ionic conductors.

Investigation of Fluorine and Nitrogen as Anionic Dopants in Nickel-Rich Cathode Materials for Lithium-Ion Batteries

Advanced lithium-ion batteries are of great interest for consumer electronics and electric vehicle applications; however, they still suffer from drawbacks stemming from cathode active material limitations (e.g., insufficient capacities and capacity fading). One approach for alleviating such limitations and stabilizing the active material structure may be anion doping. In this work, fluorine and nitrogen are investigated as potential dopants in Li_1.02(Ni_0.8Co_0.1Mn_0.1)_0.98O₂ (NCM) as a prototypical nickel-rich cathode active material. Nitrogen doping is achieved by ammonia treatment of NCM in the presence of oxygen, which serves as an unconventional and new approach. The crystal structure was investigated by means of Rietveld and pair distribution function analysis of X-ray diffraction data, which provide very precise information regarding both the average and local structure, respectively. Meanwhile, time-of-flight secondary-ion mass spectroscopy was used to assess the efficacy of dopant incorporation within the NCM structure. Moreover, scanning electron microscopy and scanning transmission electron microscopy were conducted to thoroughly investigate the dopant influences on the NCM morphology. Finally, the electrochemical performance was tested via galvanostatic cycling of half- and full-cells between 0.1 and 2 C. Ultimately, a dopant-dependent modulation of the NCM structure was found to enable the enhancement of the electrochemical performance, thereby opening a route to cathode active material optimization.

Inducing High Ionic Conductivity in the Lithium Superionic Argyrodites Li6+ xP1- xGe xS5I for All-Solid-State Batteries

Solid-state batteries with inorganic solid electrolytes are currently being discussed as a more reliable and safer future alternative to the current lithium-ion battery technology. To compete with state-of-the-art lithium-ion batteries, solid electrolytes with higher ionic conductivities are needed, especially if thick electrode configurations are to be used. In the search for optimized ionic conductors, the lithium argyrodites have attracted a lot of interest. Here, we systematically explore the influence of aliovalent substitution in Li_{6+ x}P_{1- x}Ge _xS₅I using a combination of X-ray and neutron diffraction, as well as impedance spectroscopy and nuclear magnetic resonance. With increasing Ge content, an anion site disorder is induced and the activation barrier for ionic motion drops significantly, leading to the fastest lithium argyrodite so far with 5.4 ± 0.8 mS cm^-1 in a cold-pressed state and 18.4 ± 2.7 mS cm^-1 upon sintering. These high ionic conductivities allow for successful implementation within a thick-electrode solid-state battery that shows negligible capacity fade over 150 cycles. The observed changes in the activation barrier and changing site disorder provide an additional approach toward designing better performing solid electrolytes.

Competing Structural Influences in the Li Superionic Conducting Argyrodites Li6PS5- xSe xBr (0 ≤ x ≤ 1) upon Se Substitution

Lithium-ion conducting argyrodites have recently attracted significant interest as solid electrolytes for solid-state battery applications. In order to enhance the utility of materials in this class, a deeper understanding of the fundamental structure-property relationships is still required. Using Rietveld refinements of X-ray diffraction data and pair distribution function analysis of neutron diffraction data, coupled with electrochemical impedance spectroscopy and speed of sound measurements, the structure and transport properties within Li₆PS_{5- x}Se _xBr (0 ≤ x ≤ 1) have been monitored with increasing Se content. While it has been previously suggested that the incorporation of larger, more polarizable anions within the argyrodite lattice should lead to enhancements in the ionic conductivity, the Li₆PS_{5- x}Se _xBr transport behavior was found to be largely unaffected by the incorporation of Se^2- due to significant structural modifications to the anion sublattice. This work affirms the notion that, when optimizing the ionic conductivity of solid ion conductors, local structural influences cannot be ignored and the idea of "the softer the lattice, the better" does not always hold true.

Degradation Mechanisms at the Li10GeP2S12/LiCoO2 Cathode Interface in an All-Solid-State Lithium-Ion Battery

All-solid-state batteries (ASSBs) show great potential for providing high power and energy densities with enhanced battery safety. While new solid electrolytes (SEs) have been developed with high enough ionic conductivities, SSBs with long operational life are still rarely reported. Therefore, on the way to high-performance and long-life ASSBs, a better understanding of the complex degradation mechanisms, occurring at the electrode/electrolyte interfaces is pivotal. While the lithium metal/solid electrolyte interface is receiving considerable attention due to the quest for high energy density, the interface between the active material and solid electrolyte particles within the composite cathode is arguably the most difficult to solve and study. In this work, multiple characterization methods are combined to better understand the processes that occur at the LiCoO₂ cathode and the Li₁₀GeP₂S₁₂ solid electrolyte interface. Indium and Li₄Ti₅O₁₂ are used as anode materials to avoid the instability problems associated with Li-metal anodes. Capacity fading and increased impedances are observed during long-term cycling. Postmortem analysis with scanning transmission electron microscopy, electron energy loss spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy show that electrochemically driven mechanical failure and degradation at the cathode/solid electrolyte interface contribute to the increase in internal resistance and the resulting capacity fading. These results suggest that the development of electrochemically more stable SEs and the engineering of cathode/SE interfaces are crucial for achieving reliable SSB performance.

Refinement of the crystal structure of Li4P2S6 using NMR crystallography

We report a new structural model for Li₄P₂S₆ derived from ³¹P MAS NMR and XRD data, symmetry relations and quantum-chemical calculations.

The Detrimental Effects of Carbon Additives in Li10GeP2S12-Based Solid-State Batteries

All-solid-state batteries (SSBs) have recently attracted much attention due to their potential application in electric vehicles. One key issue that is central to improve the function of SSBs is to gain a better understanding of the interfaces between the material components toward enhancing the electrochemical performance. In this work, the interfacial properties of a carbon-containing cathode composite, employing Li₁₀GeP₂S₁₂ as the solid electrolyte, are investigated. A large interfacial charge-transfer resistance builds up upon the inclusion of carbon in the composite, which is detrimental to the resulting cycle life. Analysis by X-ray photoelectron spectroscopy reveals that carbon facilitates faster electrochemical decomposition of the thiophosphate solid electrolyte at the cathode/solid electrolyte interface-by transferring the low chemical potential of lithium in the charged state deeper into the solid electrolyte and extending the decomposition region. The occurring accumulation of highly oxidized sulfur species at the interface is likely responsible for the large interfacial resistances and aggravated capacity fading observed.

Influence of Lattice Polarizability on the Ionic Conductivity in the Lithium Superionic Argyrodites Li6PS5X (X = Cl, Br, I)

In the search for novel solid electrolytes for solid-state batteries, thiophosphate ionic conductors have been in recent focus owing to their high ionic conductivities, which are believed to stem from a softer, more polarizable anion framework. Inspired by the oft-cited connection between a soft anion lattice and ionic transport, this work aims to provide evidence on how changing the polarizability of the anion sublattice in one structure affects ionic transport. Here, we systematically alter the anion framework polarizability of the superionic argyrodites Li₆PS₅X by controlling the fractional occupancy of the halide anions (X = Cl, Br, I). Ultrasonic speed of sound measurements are used to quantify the variation in the lattice stiffness and Debye frequencies. In combination with electrochemical impedance spectroscopy and neutron diffraction, these results show that the lattice softness has a striking influence on the ionic transport: the softer bonds lower the activation barrier and simultaneously decrease the prefactor of the moving ion. Due to the contradicting influence of these parameters on ionic conductivity, we find that it is necessary to tailor the lattice stiffness of materials in order to obtain an optimum ionic conductivity.

Molybdenum Oxide Nitrides of the Mo2(O,N,□)5 Type: On the Way to Mo2O5

Blue-colored molybdenum oxide nitrides of the Mo₂(O,N,□)₅ type were synthesized by direct nitridation of commercially available molybdenum trioxide with a mixture of gaseous ammonia and oxygen. Chemical composition, crystal structure, and stability of the obtained and hitherto unknown compounds are studied extensively. The average oxidation state of +5 for molybdenum is proven by Mo K near-edge X-ray absorption spectroscopy; the magnetic behavior is in agreement with compounds exhibiting Mo^VO₆ units. The new materials are stable up to ∼773 K in an inert gas atmosphere. At higher temperatures, decomposition is observed. X-ray and neutron powder diffraction, electron diffraction, and high-resolution transmission electron microscopy reveal the structure to be related to VNb₉O_24.9-type phases, however, with severe disorder hampering full structure determination. Still, the results demonstrate the possibility of a future synthesis of the potential binary oxide Mo₂O₅. On the basis of these findings, a tentative suggestion on the crystal structure of the potential compound Mo₂O₅, backed by electronic-structure and phonon calculations from first principles, is given.

Vacancy and anti-site disorder scattering in AgBiSe2 thermoelectrics

AgBiSe₂ has recently been shown to exhibit promising thermoelectric properties due to the low intrinsic thermal conductivity, stemming from a large degree of lattice anharmonicity. While samples synthesized via solid-state routes usually exhibit n-type behavior, p-type transport is seen in samples based on solution synthetic routes possibly due to Ag vacancies. Using a combined approach of synchrotron diffraction, thermoelectric transport measurements and thermal transport modeling, we show the influence of synthetically induced Ag vacancies on the structure of AgBiSe₂ and the thermoelectric transport. We identify the degree of anti-site disorder of Ag and Bi due to the occurring phase transformation and the influence of the vacancy content on metal ordering. Additionally, we show that anti-site disorder and vacancies act as scattering centers for phonons, leading to enhanced point defect scattering in this interesting thermoelectric material.

Composition-dependent surface chemistry of colloidal BaxSr1−xTiO3 perovskite nanocrystals

Ba_xSr_1−xTiO₃ perovskite nanocrystals, prepared by the vapor diffusion sol–gel method and characterized by state of the art surface techniques, display significantly different O–H stretching frequencies and adsorption properties towards CO₂ as a function of the alkaline earth composition (Ba vs. Sr).

Lanthanide-activated scheelite nanocrystal phosphors prepared by the low-temperature vapor diffusion sol–gel method

The high degree of synthetic flexibility inherent to the vapor diffusion sol–gel method has enabled the synthesis of a CaWO₄:(Eu,Tb) dual-sensitized white light emitting nanocrystal phosphor.

Low-temperature synthesis of homogeneous solid solutions of scheelite-structured Ca1−xSrxWO4 and Sr1−xBaxWO4 nanocrystals

The vapor diffusion sol–gel method was used to synthesize complex ternary scheelite nanocrystals of arbitrary and well-defined elemental stoichiometry.

Local structural investigation of Eu(3+)-doped BaTiO3 nanocrystals

A structural investigation of sub-15 nm xEu:BaTiO3 nanocrystals (x = 0-5 mol%) was conducted to determine the distribution of the Eu(3+) ion in the BaTiO3 lattice. Pair distribution function analysis of X-ray total scattering data (PDF), steady-state photoluminescence, and X-ray absorption spectroscopy (XANES/EXAFS) were employed to interrogate the crystal structure of the nanocrystals and the local atomic environment of the Eu(3+) ion. The solubility limit of the Eu(3+) ion in the nanocrystalline BaTiO3 host synthesized via the vapor diffusion sol-gel method was estimated to be ∼4 mol%. A contraction of the perovskite unit cell volume was observed upon incorporation of 1 mol% of europium, while an expansion was observed for nominal concentrations between 1 and 3 mol%. The average Eu-O distance and europium coordination number decreased from 2.46 Å and 9.9 to 2.42 Å and 8.6 for europium concentrations of 1 and 5 mol%, respectively. Structural trends were found to be consistent with the substitution of Eu(3+) for Ba(2+)via creation of a Ti(4+) vacancy at low europium concentrations (<1 mol%), and with the substitution of Eu(3+) for both Ba(2+) and Ti(4+) at high europium concentrations (1-3 mol%). The significance of accounting for local structural distortions to rationalize the distribution of lanthanide ions in the perovskite host is highlighted.

Low temperature synthesis and characterization of lanthanide-doped BaTiO3 nanocrystals

The vapor diffusion sol-gel (VDSG) method was employed for the room-temperature synthesis of ~10 nm, aliovalently doped 0.4, 0.8, and 1.6 mol% La:BaTiO3 and 0.4, 0.6, and 1.2 mol% Dy:BaTiO3 nanocrystals. Maximum ensemble relative permittivities of 176 and 208 were observed in the 0.8 mol% La:BaTiO3 and the 1.2 mol% Dy:BaTiO3 nanocrystals, respectively, relative to 89 for undoped BaTiO3 (at 1 MHz, 25 °C) due to local disorder induced by aliovalent substitution.

Hepatitis B assays in serum, plasma and whole blood on filter paper

Background

Screening and determining the immune status of individuals for hepatitis B is usually done by detecting hepatitis B surface antigen (HBsAg) and hepatitis B surface antigen-specific antibodies (HBsAb). In some countries with the highest viral burden, performing these assays is currently impractical. This paper explores the use of filter paper as a blood specimen transport medium.

Methods

Samples, chosen from routine clinical laboratory pool, were applied and dried onto filter paper. Eluates, from the paper samples, were analyzed as routine clinical specimens on ADVIA Centaur 5634® immunoassay analyzers using the standard HBsAg and HBsAb kits. Dried blood samples were subjected to a range of environmental conditions in order to assess stability.

Results

After drying and elution the assays showed linearity and precision comparable to clinical assays performed on fresh serum. Elutions at various times during a 149 day incubation period showed very little variability in the Index numbers. All analytes were temperature stable except for a decrease in the HBsAg signal at 42°C.

Conclusions

Filter paper is an acceptable storage and transport medium for serum to be used in the detection of hepatitis B markers if atmospheric variability can be controlled. HBsAg, HBsAb and HBcAb are all stable for at least five months under storage conditions below room temperature. Drying specimens, particularly serum, on filter paper at remote locations, offers a reasonable solution to the problem of hepatitis surveillance in underdeveloped regions, although some attempt at temperature control might be desirable.

Fabrication of fracture-free nanoglassified substrates by layer-by-layer deposition with a paint gun technique for real-time monitoring of protein-lipid interactions

New sensing materials that are robust, biocompatible, and amenable to array fabrication are vital to the development of novel bioassays. Herein we report the fabrication of ultrathin (ca. 5-8 nm) glass (silicate) layers on top of a gold surface for surface plasmon resonance (SPR) biosensing applications. The nanoglass layers are fabricated by layer-by-layer (LbL) deposition of poly(allylamine) hydrochloride (PAH) and sodium silicate (SiO(x)), followed by calcination at high temperature. To deposit these layers in a uniform and reproducible manner, we employed a high-volume, low-pressure (HVLP) paint gun technique that offers high precision and better control through pressurized nitrogen gas. The new substrates are stable in solution for a long period of time, and scanning electron microscopy (SEM) images confirm that these films are nearly fracture-free. In addition, atomic force microscopy (AFM) indicates that the surface roughness of the silicate layers is low (rms = 2 to 3 nm), similar to that of bare glass slides. By tuning the experimental parameters such as HVLP gun pressure and layers deposited, different surface morphology could be obtained as revealed by fluorescence microscopy and SEM images. To demonstrate the utility of these ultrathin, fracture-free substrates, lipid bilayer membranes composed of phosphorylated derivatives of phosphoinositides (PIs) were deposited on the new substrates for biosensing applications. Fluorescence recovery after photobleaching (FRAP) data indicated that these lipid components in the membranes were highly mobile. Furthermore, interactions of PtdIns(4,5)P2 and PtdIns(4)P lipids with their respective binding proteins were detected with high sensitivity by using SPR spectroscopy. This method of glass deposition can be combined with already well-developed surface chemistry for a range of planar glass assay applications, and the process is amenable to automation for mass production of nanometer thick silicate chips in a highly reproducible manner for label-free measurements.