ELECTROPHORETIC COATINGS FOR ADVANCED MATERIALS

We have electrophoretically deposited a variety of coatings for a number of applications. We have also worked extensively with a process for electrophoretically depositing styrene acrylate polymer coatings. These coatings provide useful corrosion protection and dielectric properties for capacitors and electrical insulation. Dielectric breakdown strengths in the order of 1000 V/micrometer have been observed for capacitors with this coating as the dielectric. Various particles have also been dispersed in the electrolyte; these mixtures yield composite coatings of unusual materials such as fissile uranium in a carbon matrix. The process can also be adapted to form very thin, free-standing styrene acrylate films or pellicles. We have also explored the feasibility of depositing a variety of colloidal inorganic particles from liquid suspensions. Our results show that isopropanol works relatively well as a dispersing medium for a large number of powders. Isopropanol slurries can be used to deposit a number of uniform ceramic or glass coatings on metal substrates. Important coating considerations with regard to whether useful coatings can be deposited using this latter type of electrophoretic process include: (1) the average size, size distribution, and shape of the particles, (2) the charge assumed by the powder particles when they are dispersed in a liquid such as isopropanol, and (3) the coefficients of thermal expansion of the substrate and the coating material from the standpoint of the heat treatment or sintering required to obtain sufficient cohesion and adhesion.     

Double‐Layer Polymer Electrolyte for High‐Voltage All‐Solid‐State Rechargeable Batteries

No single polymer or liquid electrolyte has a large enough energy gap between the empty and occupied electronic states for both dendrite‐free plating of a lithium‐metal anode and a Li⁺ extraction from an oxide host cathode without electrolyte oxidation in a high‐voltage cell during the charge process. Therefore, a double‐layer polymer electrolyte is investigated, in which one polymer provides dendrite‐free plating of a Li‐metal anode and the other allows a Li⁺ extraction from an oxide host cathode without oxidation of the electrolyte in a 4 V cell over a stable charge/discharge cycling at 65 °C; a poly(ethylene oxide) polymer contacts the lithium‐metal anode and a poly(N‐methyl‐malonic amide) contacts the cathode. All interfaces of the flexible, plastic electrolyte remain stable with no visible reduction of the Li⁺ conductivity on crossing the polymer/polymer interface.     

The Valve Metal Character of Zirconium as inferred from anode potential measurements in mineral acid solutions

A study on the value metal character of Zr in 0.1 M solutions of H₂SO₄, HNO₃, and H₃PO₄ has been performed using the anode potential as the primary variable in galvanostatic, potentiostatic, and capacity measurements. A method of surface pre-treatment, which suppresses both O₂ evolution and metal dissolution, has been described. Kinetic parameters of oxide growth have been calculated. The results indicate that:

• (i) the high field approximation is applicable following an exponential law, and
• (ii) the height and activation distance of the energy barrier for ion transport through the oxide phase (Verwey model) are the same three acids.

Measurements have been also made on the dielectric breakdown of oxide, and this occurs at potentials above 200 V. Direct capacity measurements give similar results as those based on reciprocal capacity calculated from galvanostatic experiments. It is concluded that the dominant anodic oxide species is ZrO₂ having a dielectric constant of 25. Open circuit potential measurements show that Zr is spontaneously oxidized in the three acids.     

Investigations of diffusion behaviour in Al-doped zinc oxide and zinc stannate coatings

Multi-layer dielectric/silver/dielectric coating systems have excellent proprieties as heat insulators and for solar energy reflection and electrical conductivity. The largest market is dominated by low-emissivity (low-E) coatings, which are applied to large area architectural glazing to reduce heat losses from buildings. They combine high visible transparency with high reflectance in the far-infrared region, where the thin (~ 10 nm) silver layer reflects long wavelength IR back into the building and the dielectric layers both protect the silver and act as anti reflectance layers.In this study, a range of dielectric coatings has been deposited onto soda-lime glass substrates by reactive sputtering from metallic targets. The magnetrons were driven in DC mode and also in mid-frequency pulsed DC and AC modes. Process variables investigated include operating pressure, oxygen flow rate and magnetron configuration. Selected coatings were annealed at 650 °C and analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscope (AFM).The oxide samples were then over-coated with silver and annealed for a second time. These coatings were analysed by secondary ion mass spectroscopy (SIMS) to determine the diffusion rates of silver and sodium (from the substrate) through the oxide coatings.The results to date, presented here, show the diffusion of silver and sodium atoms through zinc oxide and zinc stannate thin films deposited under a vast range of conditions. Preliminary attempts have been made to estimate diffusion coefficients for these coating systems and to relate these values to processing conditions and the structural variations observed.     

Polymer electrolytes and interfaces in solid-state lithium metal batteries

The polymer electrolyte based solid-state lithium metal batteries are the promising candidate for the high-energy electrochemical energy storage with high safety and stability. Moreover, the intrinsic properties of polymer electrolytes and interface contact between electrolyte and electrodes have played critical roles for determining the comprehensive performances of solid-state lithium metal batteries. In this review, the development of polymer electrolytes with the design strategies by functional units adjustments are firstly discussed. Then the interfaces between polymer electrolyte and cathode/anode, including the interface issues, remedy strategies for stabilizing the interface contact and reducing resistances, and the in-situ polymerization method for enhancing the compatibilities and assembling the batteries with favorable performances, have been introduced. Lastly, the perspectives on developing polymer electrolytes by functional units adjustment, and improving interface contact and stability by effective strategies for solid-state lithium metal batteries have been provided.     

Protected Lithium‐Metal Anodes in Batteries: From Liquid to Solid

High‐energy lithium‐metal batteries are among the most promising candidates for next‐generation energy storage systems. With a high specific capacity and a low reduction potential, the Li‐metal anode has attracted extensive interest for decades. Dendritic Li formation, uncontrolled interfacial reactions, and huge volume effect are major hurdles to the commercial application of Li‐metal anodes. Recent studies have shown that the performance and safety of Li‐metal anodes can be significantly improved via organic electrolyte modification, Li‐metal interface protection, Li‐electrode framework design, separator coating, and so on. Superior to the liquid electrolytes, solid‐state electrolytes are considered able to inhibit problematic Li dendrites and build safe solid Li‐metal batteries. Inspired by the bright prospects of solid Li‐metal batteries, increasing efforts have been devoted to overcoming the obstacles of solid Li‐metal batteries, such as low ionic conductivity of the electrolyte and Li–electrolyte interfacial problems. Here, the approaches to protect Li‐metal anodes from liquid batteries to solid‐state batteries are outlined and analyzed in detail. Perspectives regarding the strategies for developing Li‐metal anodes are discussed to facilitate the practical application of Li‐metal batteries.     

Reviving Lithium‐Metal Anodes for Next‐Generation High‐Energy Batteries

Lithium‐metal batteries (LMBs), as one of the most promising next‐generation high‐energy‐density storage devices, are able to meet the rigid demands of new industries. However, the direct utilization of metallic lithium can induce harsh safety issues, inferior rate and cycle performance, or anode pulverization inside the cells. These drawbacks severely hinder the commercialization of LMBs. Here, an up‐to‐date review of the behavior of lithium ions upon deposition/dissolution, and the failure mechanisms of lithium‐metal anodes is presented. It has been shown that the primary causes consist of the growth of lithium dendrites due to large polarization and a strong electric field at the vicinity of the anode, the hyperactivity of metallic lithium, and hostless infinite volume changes upon cycling. The recent advances in liquid organic electrolyte (LOE) systems through modulating the local current density, anion depletion, lithium flux, the anode–electrolyte interface, or the mechanical strength of the interlayers are highlighted. Concrete strategies including tailoring the anode structures, optimizing the electrolytes, building artificial anode–electrolyte interfaces, and functionalizing the protective interlayers are summarized in detail. Furthermore, the challenges remaining in LOE systems are outlined, and the future perspectives of introducing solid‐state electrolytes to radically address safety issues are presented.     

Effect of process parameters on coating composition of cathodic-plasma-electrolysis-treated copper

Cathodic plasma electrolysis is a novel technique to form nanostructured layers on metallic surfaces by application of high voltage in a suitable aqueous electrolyte. In the present study, copper is treated by plasma electrolysis in 50 vol% ethanol electrolyte and coatings comprising carbon nanostructure and copper oxide are formed on the copper. The effect of some process parameters such as electrical conductivity, volume and temperature of electrolyte and ratio of anode to cathode surface area on current–voltage behaviour and subsequently coating compositions are investigated at 150 V deposition voltage. The composition and morphology of these coatings are characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. Different current–voltage behaviours, temperatures of substrate and the contents and energies of radicals and ions around the substrate by changes in the mentioned parameters cause different compositions from 100 vol% copper oxide to different ratios of copper oxide to carbon, the structure changing from amorphous to graphitic structure in carbon and amorphous to cubic morphology in copper oxide on the substrate. Therefore, the understanding of cathodic plasma electrolysis can be developed.     

Characteristics of barrier anodized coatings on 6061 aluminum alloy

We have evaluated the characteristics of anodic coatings on 6061 aluminum alloy. We grew these coatings using a high voltage (950 V) low current density (1–2 mA cm^-2) high resistivity (45–75 kΩ cm) process in an electrolyte consisting of a solution of ammonium tartrate in ethanol. Coating properties which we subsequently characterized include thickness, density, morphology, entrained and adsorbed impurities, dielectric constant, breakdown strength and leakage curent. A comparison of the coatings on 6061 aluminum alloy with coatings grown using similar conditions on commercially pure 1100 aluminum alloy indicates that the alloying components in 6061 aluminum affect subsequent coating morphology and dielectric properties. The coatings displayed useful dielectric properties. The fact that these coatings were grown on 6061 aluminum alloy, which is a common industrial alloy used because of its relatively high strength and machinability, may recommend these coatings for a variety of practical applications.     

HWCVD MoO3 nanoparticles and a-Si for next generation Li-ion anodes

We have employed hot wire chemical vapor deposition (HWCVD) for the generation of MoO₃ nanostructures at high density. Furthermore, the morphology of the nanoparticles is easily tailored by altering the HWCVD synthesis conditions. The MoO₃ nanoparticles have been demonstrated as high-capacity Li-ion battery anodes for next-generation electric vehicles. Specifically, the MoO₃ anodes have been shown to have approximately three times the Li-ion capacity of commercially employed graphite anodes in thick electrodes suitable for vehicular applications. However because the materials are high volume expansion materials (≥ 100%), conformal Al₂O₃ coatings deposited with atomic layer deposition (ALD) were required before high rate capability was demonstrated. Recently, NREL is exploring high capacity Si anode materials that have a volume expansion of ~ 400%. It is assumed that new ALD coatings will need to be developed in order to stabilize Si as an anode material. Silicon is a superior choice for an anode material to the metal oxide structures due to both a higher capacity and a significantly lower hysteresis in the voltage vs. Li/Li⁺ for the charge/discharge profiles.     

The ionic interphases of the lithium anode in solid state batteries

Solid state battery (SSB) performance is largely governed by processes occurring at electrolyte–electrode interfaces. At the Li metal anode, where the overwhelming majority of solid electrolyte (SE) are unstable against Li metal, the interface can readily react to form emergent Li-solid electrolyte interphases (SEI) with ionic, electronic, chemical, mechanical, and electrochemical properties substantially distinct from the parent phase. Facing similar challenges with liquid electrolytes, the Li battery community underwent a half century-long effort, still in progress, to illuminate fundamental properties of the Li SEI—including chemistry, morphology, transport, and sources of Li loss upon cycling—from which guiding principles have emerged to drive improvement in electrolyte and interface design. The Li metal SEI with solid electrolytes presents both similarities and differences to that in liquid electrolytes, with differences defining unique research needs. Here, we examine current understanding of the Li-SE interface as well as learnings from the liquid electrolyte community that we propose might be adopted to help rationalize and improve SE integration with Li anodes. Through this lens, we inspect current state-of-understanding of Li SEI composition, structure, and properties, along with Coulombic efficiency values reported so far for Li cycling with SE. We also highlight potential Li modification strategies for SSB, which are informed by and exploit understanding of the ionic SEI phases; in some instances, engineering strategies utilize a liquid electrolyte SEI directly, making liquid-derived SEI knowledge of immediate relevance.     

Colossal Granular Lithium Deposits Enabled by the Grain-Coarsening Effect for High-Efficiency Lithium Metal Full Batteries

The low Coulombic efficiency of the lithium metal anode is recognized as the real bottleneck to practical high-efficiency lithium metal batteries with limited Li excess. The grain size and microstructure of deposited lithium strongly influences the lithium plating/stripping efficiency. Here, a solubilizer-mediated carbonate electrolyte that can realize grain coarsening of lithium deposits (>20 µm in width) with oriented columnar morphology, which is in sharp contrast with conventional nanoscale dendrite-like lithium deposits in carbonate electrolytes, is reported. It exhibits improved Li Coulombic efficiency to 98.14% at a high capacity of 3 mAh cm⁻² over 150 cycles, because the colossal lithium deposition with minimal tortuosity can maintain the bulk Li with continuous electron conducting pathway during the stripping process, thus enabling efficient Li utilization. Li/NMC811 full batteries, composed of thin Li anode (45 µm) and a high-capacity NMC811 cathode (16.7 mg cm⁻²), can achieve at least 12 times longer lifespan (200 cycles).     

Electroplating of zirconium and aluminum hydroxide thin films following anodic dissolution of corresponding metal anodes in organic medium

Zirconium (IV) hydroxide or hydrate oxide films, which are typically difficult to prepare by electrochemical methods using aqueous solutions, are easily fabricated in an acetone bath using Zr anodes as the metal sources and a metal-free solvent containing halide ions as the supporting electrolyte. This method is also confirmed to be applicable to aluminum anodes. In the early stage of electrolysis, anodic oxidation of the metal anode proceeds in the presence of water as an impurity in the solvent. Subsequently, pitting corrosion of the oxide film on the metal anode occurs as a result of the action of halide ions. The corrosiveness of the halogen additive appears to be an important factor determining the dissolution or deposition of metal species in this stage. That is, Br^– is more active for electrochemical dissolution of a passive oxide film on the anode compared to I^–. Finally, Zr species are deposited on the cathode surface via reactions with cathodically generated hydroxide ions. In these processes, the metal plate acts as a soluble anode and as a metal source for electrodeposition. The coating of Zr (IV) hydroxide film on a stainless steel substrate is shown to act as an effective barrier against electrolytic corrosion.     

Coupling of conductivity to the relaxation process in polymer electrolytes

Conductivity relaxation using modulus formalism has been used to explore the coupling of ionic conductivity to dielectric relaxation in polymer electrolyte based on polyethylene oxide complexed with various content of LiAsF₆. The temperature dependence of conductivity followed the VTF behavior suggesting close correlation between conductivity and the segmental relaxation process in polymer electrolytes. The coupling of conductivity to the segmental process has been discussed in terms of coupling index. For all compositions studied, the coupling index was within the range of 1–11 in the temperature range of investigation, which was in agreement with the coupled systems.     

Electrolytic Metallic Coatings for Carbon Fibers

This paper concerns electrolytic metallic coatings for carbon fibers and the related processes. Plating bath design, electrolyte selection and other aspects were investigated. Experimental results especially in copper electroplating show that the uniformity of metallic coatings on carbon fibers can be improved by the modification of plating bath and the selection of electrolytes. Thus continuous and uniform metallic coatings can be obtained on carbon fibers, even if the cross section of carbon fibers has irregular shape. Polarization tests on different copper baths was performed. Electrodeposition of other metallic layers such as nickel, cobalt, and copper/tin duplex layer was also introduced. A process of two or more than two plating steps in which different electrolytes may be used for same metal deposition was proposed to expedite the coating procedure     

Investigation of Galvanic Chromous Structures

X-ray methods have been used to study the structure of galvanic chromous coatings, which were deposited by chrome acid electrolytes with different additions. The possibility of producing crystalline and amorphous chromous deposits has been established using x-rays. The influence of thermo-processing on the structure and some mechanical characteristics of coatings were investigated. It was shown that during the process of heating, the hardness of crystalline deposits reduced dramatically at about 400^°C. At the same time it was observed that the hardness of amorphous deposits increased significantly.     

Rapidly Constructing Sodium Fluoride-Rich Interface by Pressure and Diglyme-Induced Defluorination Reaction for Stable Sodium Metal Anode

Sodium (Na) metal is able to directly use as a battery anode but have a highly reductive ability of unavoidably occurring side reactions with organic electrolytes, resulting in interfacial instability as a primary factor in performance decay. Therefore, building stable Na metal anode is of utmost significance for both identifying the electrochemical performance of laboratory half-cells employed for quantifying samples and securing the success of room-temperature Na metal batteries. In this work, we propose an NaF-rich interface rapidly prepared by pressure and diglyme-induced defluorination reaction for stable Na metal anode. Once the electrolyte is dropped into the coin-type cells followed by a slight squeeze, the Na metal surface immediately forms a protective layer consisting of amorphous carbon and NaF, effectively inhibiting the dendrite growth and dead Na. The resultant Na metal anode exhibits a long-term cycling lifespan over 1800 h even under the area capacity of 3.0 mAh cm⁻². Furthermore, such a universal and facile method is readily applied in daily battery assembly regarding Na metal anode.     

Ferroelastic toughening: Can it solve the mechanics challenges of solid electrolytes?

The most promising solid electrolytes for all-solid-state Li batteries are oxide and sulfide ceramics. Current ceramic solid electrolytes are brittle and lack the toughness to withstand the mechanical stresses of repeated charge and discharge cycles. Solid electrolytes are susceptible to crack propagation due to dendrite growth from Li metal anodes and to debonding processes at the cathode/electrolyte interface due to cyclic variations in the cathode lattice parameters. In this perspective, we argue that solutions to the mechanics challenges of all-solid-state batteries can be borrowed from the aerospace industry, which successfully overcame similar hurdles in the development of thermal barrier coatings of superalloy turbine blades. Their solution was to exploit ferroelastic and transformation toughening mechanisms to develop ceramics that can withstand cyclic stresses due to large variations in temperature. This perspective describes fundamental materials design principles with which to search for solid electrolytes that are ferroelastically toughened.     

Tuning the Anode–Electrolyte Interface Chemistry for Garnet-Based Solid-State Li Metal Batteries

Lithium (Li) metal is a promising candidate as the anode for high-energy-density solid-state batteries. However, interface issues, including large interfacial resistance and the generation of Li dendrites, have always frustrated the attempt to commercialize solid-state Li metal batteries (SSLBs). Here, it is reported that infusing garnet-type solid electrolytes (GSEs) with the air-stable electrolyte Li₃PO₄ (LPO) dramatically reduces the interfacial resistance to ≈1 Ω cm² and achieves a high critical current density of 2.2 mA cm⁻² under ambient conditions due to the enhanced interfacial stability to the Li metal anode. The coated and infused LPO electrolytes not only improve the mechanical strength and Li-ion conductivity of the grain boundaries, but also form a stable Li-ion conductive but electron-insulating LPO-derived solid-electrolyte interphase between the Li metal and the GSE. Consequently, the growth of Li dendrites is eliminated and the direct reduction of the GSE by Li metal over a long cycle life is prevented. This interface engineering approach together with grain-boundary modification on GSEs represents a promising strategy to revolutionize the anode–electrolyte interface chemistry for SSLBs and provides a new design strategy for other types of solid-state batteries.     

钛合金微弧氧化一步制备含石墨的减摩涂层

为了进一步提高钛合金表面微弧氧化陶瓷涂层的摩擦磨损性能,在石墨分散的Na2CO3-Na2SiO3-KOH电解液溶液中一步制备了含自润滑微粒的微弧氧化复合涂层.利用X射线衍射仪(XRD)、X射线光电子能谱仪(XPS)和扫描电子显微镜(SEM)研究了未添加和添加石墨微弧氧化涂层的相组成和微结构,采用往复式球-盘试验机评价了两种涂层的摩擦学性能.结果表明:加入到电解液中的石墨在微弧氧化过程中进入到涂层中,从而得到含有固体润滑微粒的复合涂层;在干摩擦条件下,含石墨的微弧氧化涂层相比于不含石墨的涂层具有更小的摩擦系数.