Showing papers by "Yi Cui published in 2018"

High-efficiency oxygen reduction to hydrogen peroxide catalysed by oxidized carbon materials

Abstract: Hydrogen peroxide (H2O2) is a valuable chemical with a wide range of applications, but the current industrial synthesis of H2O2 involves an energy-intensive anthraquinone process. The electrochemical synthesis of H2O2 from oxygen reduction offers an alternative route for on-site applications; the efficiency of this process depends greatly on identifying cost-effective catalysts with high activity and selectivity. Here, we demonstrate a facile and general approach to catalyst development via the surface oxidation of abundant carbon materials to significantly enhance both the activity and selectivity (~90%) for H2O2 production by electrochemical oxygen reduction. We find that both the activity and selectivity are positively correlated with the oxygen content of the catalysts. The density functional theory calculations demonstrate that the carbon atoms adjacent to several oxygen functional groups (–COOH and C–O–C) are the active sites for oxygen reduction reaction via the two-electron pathway, which are further supported by a series of control experiments. The direct synthesis of hydrogen peroxide via oxygen reduction is an attractive alternative to the anthraquinone process. Here, a general trend linking oxygenation of carbon surfaces with electrocatalytic performance in peroxide synthesis is demonstrated, and computational studies provide further insight into the nature of the active sites.

Materials for lithium-ion battery safety

Abstract: Lithium-ion batteries (LIBs) are considered to be one of the most important energy storage technologies. As the energy density of batteries increases, battery safety becomes even more critical if the energy is released unintentionally. Accidents related to fires and explosions of LIBs occur frequently worldwide. Some have caused serious threats to human life and health and have led to numerous product recalls by manufacturers. These incidents are reminders that safety is a prerequisite for batteries, and serious issues need to be resolved before the future application of high-energy battery systems. This Review aims to summarize the fundamentals of the origins of LIB safety issues and highlight recent key progress in materials design to improve LIB safety. We anticipate that this Review will inspire further improvement in battery safety, especially for emerging LIBs with high-energy density.

Robust and conductive two-dimensional metal−organic frameworks with exceptionally high volumetric and areal capacitance

Abstract: For miniaturized capacitive energy storage, volumetric and areal capacitances are more important metrics than gravimetric ones because of the constraints imposed by device volume and chip area. Typically used in commercial supercapacitors, porous carbons, although they provide a stable and reliable performance, lack volumetric performance because of their inherently low density and moderate capacitances. Here we report a high-performing electrode based on conductive hexaaminobenzene (HAB)-derived two-dimensional metal−organic frameworks (MOFs). In addition to possessing a high packing density and hierarchical porous structure, these MOFs also exhibit excellent chemical stability in both acidic and basic aqueous solutions, which is in sharp contrast to conventional MOFs. Submillimetre-thick pellets of HAB MOFs showed high volumetric capacitances up to 760 F cm−3 and high areal capacitances over 20 F cm−2. Furthermore, the HAB MOF electrodes exhibited highly reversible redox behaviours and good cycling stability with a capacitance retention of 90% after 12,000 cycles. These promising results demonstrate the potential of using redox-active conductive MOFs in energy-storage applications. Metal–organic frameworks (MOFs) are attractive electrodes for supercapacitors but generally suffer from low electric conductivity and chemical stability. Here the authors report stable conductive MOFs based on hexaminobenzene linker with volumetric and areal capacitances in excess of 700 F per cm3 and 15 F per cm2, respectively.

A Silica-Aerogel-Reinforced Composite Polymer Electrolyte with High Ionic Conductivity and High Modulus.

Abstract: High-energy all-solid-state lithium (Li) batteries have great potential as next-generation energy-storage devices. Among all choices of electrolytes, polymer-based systems have attracted widespread attention due to their low density, low cost, and excellent processability. However, they are generally mechanically too weak to effectively suppress Li dendrites and have lower ionic conductivity for reasonable kinetics at ambient temperature. Herein, an ultrastrong reinforced composite polymer electrolyte (CPE) is successfully designed and fabricated by introducing a stiff mesoporous SiO2 aerogel as the backbone for a polymer-based electrolyte. The interconnected SiO2 aerogel not only performs as a strong backbone strengthening the whole composite, but also offers large and continuous surfaces for strong anion adsorption, which produces a highly conductive pathway across the composite. As a consequence, a high modulus of ≈0.43 GPa and high ionic conductivity of ≈0.6 mS cm-1 at 30 °C are simultaneously achieved. Furthermore, LiFePO4 -Li full cells with good cyclability and rate capability at ambient temperature are obtained. Full cells with cathode capacity up to 2.1 mAh cm-2 are also demonstrated. The aerogel-reinforced CPE represents a new design principle for solid-state electrolytes and offers opportunities for future all-solid-state Li batteries.

Solubility-mediated sustained release enabling nitrate additive in carbonate electrolytes for stable lithium metal anode.

Abstract: The physiochemical properties of the solid-electrolyte interphase, primarily governed by electrolyte composition, have a profound impact on the electrochemical cycling of metallic lithium. Herein, we discover that the effect of nitrate anions on regulating lithium deposition previously known in ether-based electrolytes can be extended to carbonate-based systems, which dramatically alters the nuclei from dendritic to spherical, albeit extremely limited solubility. This is attributed to the preferential reduction of nitrate during solid-electrolyte interphase formation, and the mechanisms behind which are investigated based on the structure, ion-transport properties, and charge transfer kinetics of the modified interfacial environment. To overcome the solubility barrier, a solubility-mediated sustained-release methodology is introduced, in which nitrate nanoparticles are encapsulated in porous polymer gel and can be steadily dissolved during battery operation to maintain a high concentration at the electroplating front. As such, effective dendrite suppression and remarkably enhanced cycling stability are achieved in corrosive carbonate electrolytes.

Nanoporous polyethylene microfibres for large-scale radiative cooling fabric

Abstract: Global warming and energy crises severely limit the ability of human civilization to develop along a sustainable path. Increasing renewable energy sources and decreasing energy consumption are fundamental steps to achieve sustainability. Technological innovations that allow energy-saving behaviour can support sustainable development pathways. Energy-saving fabrics with a superior cooling effect and satisfactory wearability properties provide a novel way of saving the energy used by indoor cooling systems. Here, we report the large-scale extrusion of uniform and continuous nanoporous polyethylene (nanoPE) microfibres with cotton-like softness for industrial fabric production. The nanopores embedded in the fibre effectively scatter visible light to make it opaque without compromising the mid-infrared transparency. Moreover, using industrial machines, the nanoPE microfibres are utilized to mass produce fabrics. Compared with commercial cotton fabric of the same thickness, the nanoPE fabric exhibits a great cooling power, lowering the human skin temperature by 2.3 °C, which corresponds to a greater than 20% saving on indoor cooling energy. Besides the superior cooling effect, the nanoPE fabric also displays impressive wearability and durability. As a result, nanoPE microfibres represent basic building blocks to revolutionize fabrics for human body cooling and pave an innovative way to sustainable energy. Energy-saving innovations, such as fabrics with cooling effects, contribute to sustainability. This study reports the large-scale extrusion of uniform and continuous nanoporous polyethylene microfibres with cotton-like softness for wearable fabrics. The fabric can lower human skin temperature by 2.3 °C with over 20% savings on indoor cooling energy.

Spectrally Selective Nanocomposite Textile for Outdoor Personal Cooling

Abstract: Outdoor heat stress poses a serious public health threat and curtails industrial labor supply and productivity, thus adversely impacting the wellness and economy of the entire society. With climate change, there will be more intense and frequent heat waves that further present a grand challenge for sustainability. However, an efficient and economical method that can provide localized outdoor cooling of the human body without intensive energy input is lacking. Here, a novel spectrally selective nanocomposite textile for radiative outdoor cooling using zinc oxide nanoparticle-embedded polyethylene is demonstrated. By reflecting more than 90% solar irradiance and selectively transmitting out human body thermal radiation, this textile can enable simulated skin to avoid overheating by 5-13 °C compared to normal textile like cotton under peak daylight condition. Owing to its superior passive cooling capability and compatibility with large-scale production, this radiative outdoor cooling textile is promising to widely benefit the sustainability of society in many aspects spanning from health to economy.

Stabilization of Hexaaminobenzene in a 2D Conductive Metal–Organic Framework for High Power Sodium Storage

Abstract: Redox-active organic materials have gained growing attention as electrodes of rechargeable batteries However, their key limitations are the low electronic conductivity and limited chemical and str

Concentrated mixed cation acetate “water-in-salt” solutions as green and low-cost high voltage electrolytes for aqueous batteries

Abstract: Electrolyte solutions are a key component of energy storage devices that significantly impact capacity, safety, and cost. Recent developments in “water-in-salt” (WIS) aqueous electrolyte research have enabled the demonstration of aqueous Li-ion batteries that operate with capacities and cyclabilities comparable with those of commercial non-aqueous Li-ion batteries. Critically, the use of aqueous electrolyte mitigates safety risks associated with non-aqueous electrolytes. However, the high cost and potential toxicity of imide-based WIS electrolytes limit their practical deployment. In this report, we disclose the efficacy of inexpensive, non-toxic mixed cation electrolyte systems for Li-ion batteries that otherwise provide the same benefits as current WIS electrolytes: extended electrochemical stability window and compatibility with traditional intercalation Li-ion battery electrode materials. We take advantage of the high solubility of potassium acetate to achieve the WIS condition in a eutectic mixture of lithium and potassium acetate with water-to-cation ratio as low as 1.3. Our work suggests an important direction for the practical realization of safe, low-cost, and high-performance aqueous Li-ion batteries.

Efficient electrocatalytic CO 2 reduction on a three-phase interface

Abstract: Electrochemical CO2 reduction is a critical approach to reducing the globally accelerating CO2 emission and generating value-added products. Despite great efforts to optimize catalyst activity and selectivity, facilitating the catalyst accessibility to high CO2 concentrations while maintaining electrode durability remains a significant challenge. Here, we designed a catalytic system that mimics the alveolus structure in mammalian lungs with high gas permeability but very low water diffusibility, enabling an array of three-phase catalytic interfaces. Flexible, hydrophobic, nanoporous polyethylene membranes with high gas permeability were used to enable efficient CO2 access and a high local alkalinity on the catalyst surface at different CO2 flow rates. Such an alveolus-mimicking structure generates a high CO production Faradaic efficiency of 92% and excellent geometric current densities of CO production (25.5 mA cm−2) at −0.6 V versus the reversible hydrogen electrode, with a very thin catalyst thickness of 20−80 nm. The efficient design of electrochemical CO2 reduction catalysts requires high CO2 concentrations on the catalyst surface. Here, Cui and co-workers make use of flexible, hydrophobic, nanoporous polyethylene membranes with good gas permeability to design a catalytic set-up that mimics the alveolus structure in mammalian lungs, achieving high activity and selectivity to CO.

Effects of Polymer Coatings on Electrodeposited Lithium Metal

Abstract: The electrodeposition of lithium metal is a key process in next-generation, high energy density storage devices. However, the high reactivity of the lithium metal causes short cycling lifetimes and dendrite growth that can pose a serious safety issue. Recently, a number of approaches have been pursued to stabilize the lithium metal–electrolyte interface, including soft polymeric coatings that have shown the ability to enable high-rate and high-capacity lithium metal cycling, but a clear understanding of how to design and modify these coatings has not yet been established. In this work, we studied the effects of several polymers with systematically varied chemical and mechanical properties as coatings on the lithium metal anode. By examining the early stages of lithium metal deposition, we determine that the morphology of the lithium particles is strongly influenced by the chemistry of the polymer coating. We have identified polymer dielectric constant and surface energy as two key descriptors of the lithi...

A manganese–hydrogen battery with potential for grid-scale energy storage

Abstract: Batteries including lithium-ion, lead–acid, redox-flow and liquid-metal batteries show promise for grid-scale storage, but they are still far from meeting the grid's storage needs such as low cost, long cycle life, reliable safety and reasonable energy density for cost and footprint reduction. Here, we report a rechargeable manganese–hydrogen battery, where the cathode is cycled between soluble Mn2+ and solid MnO2 with a two-electron reaction, and the anode is cycled between H2 gas and H2O through well-known catalytic reactions of hydrogen evolution and oxidation. This battery chemistry exhibits a discharge voltage of ~1.3 V, a rate capability of 100 mA cm−2 (36 s of discharge) and a lifetime of more than 10,000 cycles without decay. We achieve a gravimetric energy density of ~139 Wh kg−1 (volumetric energy density of ~210 Wh l−1), with the theoretical gravimetric energy density of ~174 Wh kg−1 (volumetric energy density of ~263 Wh l−1) in a 4 M MnSO4 electrolyte. The manganese–hydrogen battery involves low-cost abundant materials and has the potential to be scaled up for large-scale energy storage.

Spatially controlled doping of two-dimensional SnS 2 through intercalation for electronics

Abstract: Doped semiconductors are the most important building elements for modern electronic devices 1 . In silicon-based integrated circuits, facile and controllable fabrication and integration of these materials can be realized without introducing a high-resistance interface2,3. Besides, the emergence of two-dimensional (2D) materials enables the realization of atomically thin integrated circuits4–9. However, the 2D nature of these materials precludes the use of traditional ion implantation techniques for carrier doping and further hinders device development 10 . Here, we demonstrate a solvent-based intercalation method to achieve p-type, n-type and degenerately doped semiconductors in the same parent material at the atomically thin limit. In contrast to naturally grown n-type S-vacancy SnS2, Cu intercalated bilayer SnS2 obtained by this technique displays a hole field-effect mobility of ~40 cm2 V−1 s−1, and the obtained Co-SnS2 exhibits a metal-like behaviour with sheet resistance comparable to that of few-layer graphene 5 . Combining this intercalation technique with lithography, an atomically seamless p–n–metal junction could be further realized with precise size and spatial control, which makes in-plane heterostructures practically applicable for integrated devices and other 2D materials. Therefore, the presented intercalation method can open a new avenue connecting the previously disparate worlds of integrated circuits and atomically thin materials. Intercalation of copper and cobalt atoms into n-type SnS2 enables seamless integration of metal, and n- and p-type semiconductors in one parent 2D material.

Vertically Aligned and Continuous Nanoscale Ceramic–Polymer Interfaces in Composite Solid Polymer Electrolytes for Enhanced Ionic Conductivity

Abstract: Among all solid electrolytes, composite solid polymer electrolytes, comprised of polymer matrix and ceramic fillers, garner great interest due to the enhancement of ionic conductivity and mechanical properties derived from ceramic–polymer interactions. Here, we report a composite electrolyte with densely packed, vertically aligned, and continuous nanoscale ceramic–polymer interfaces, using surface-modified anodized aluminum oxide as the ceramic scaffold and poly(ethylene oxide) as the polymer matrix. The fast Li+ transport along the ceramic–polymer interfaces was proven experimentally for the first time, and an interfacial ionic conductivity higher than 10–3 S/cm at 0 °C was predicted. The presented composite solid electrolyte achieved an ionic conductivity as high as 5.82 × 10–4 S/cm at the electrode level. The vertically aligned interfacial structure in the composite electrolytes enables the viable application of the composite solid electrolyte with superior ionic conductivity and high hardness, allowin...

Atomic layer deposition of stable lithium ion conductive interfacial layer for stable cathode cycling

Abstract: A coated cathode material includes a cathode active material and an interfacial layer coating the cathode active material. The interfacial layer includes a lithium-containing fluoride which includes at least one additional metal different from lithium.

Wood-Inspired High-Performance Ultrathick Bulk Battery Electrodes.

Abstract: Ultrathick electrode design is a promising strategy to enhance the specific energy of Li-ion batteries (LIBs) without changing the underlying materials chemistry. However, the low Li-ion conductivity caused by ultralong Li-ion transport pathway in traditional random microstructured electrode heavily deteriorates the rate performance of ultrathick electrodes. Herein, inspired by the vertical microchannels in natural wood as the highway for water transport, the microstructures of wood are successfully duplicated into ultrathick bulk LiCoO2 (LCO) cathode via a sol-gel process to achieve the high areal capacity and excellent rate capability. The X-ray-based microtomography demonstrates that the uniform microchannels are built up throughout the whole wood-templated LCO cathode bringing in 1.5 times lower of tortuosity and ≈2 times higher of Li-ion conductivity compared to that of random structured LCO cathode. The fabricated wood-inspired LCO cathode delivers high areal capacity up to 22.7 mAh cm-2 (five times of the existing electrode) and achieves the dynamic stress test at such high areal capacity for the first time. The reported wood-inspired design will open a new avenue to adopt natural hierarchical structures to improve the performance of LIBs.

Flexible and stable high-energy lithium-sulfur full batteries with only 100% oversized lithium

Abstract: Lightweight and flexible energy storage devices are urgently needed to persistently power wearable devices, and lithium-sulfur batteries are promising technologies due to their low mass densities and high theoretical capacities. Here we report a flexible and high-energy lithium-sulfur full battery device with only 100% oversized lithium, enabled by rationally designed copper-coated and nickel-coated carbon fabrics as excellent hosts for lithium and sulfur, respectively. These metallic carbon fabrics endow mechanical flexibility, reduce local current density of the electrodes, and, more importantly, significantly stabilize the electrode materials to reach remarkable Coulombic efficiency of >99.89% for a lithium anode and >99.82% for a sulfur cathode over 400 half-cell charge-discharge cycles. Consequently, the assembled lithium-sulfur full battery provides high areal capacity (3 mA h cm−2), high cell energy density (288 W h kg−1 and 360 W h L−1), excellent cycling stability (260 cycles), and remarkable bending stability at a small radius of curvature (<1 mm). Lightweight and flexible energy storage devices are needed to persistently power wearable devices. Here the authors employ metallized carbon fabrics as hosts for sulfur and lithium to achieve flexibility, electrochemical stability and high energy density in a lithium-sulfur battery.

Robust Pinhole-free Li3N Solid Electrolyte Grown from Molten Lithium.

Abstract: Lithium metal is the ultimate anode choice for high energy density rechargeable lithium batteries. However, it suffers from inferior electrochemical performance and safety issues due to its high reactivity and the growth of lithium dendrites. It has long been desired to develop a materials coating on Li metal, which is pinhole-free, mechanically robust without fracture during Li metal deposition and stripping, and chemically stable against Li metal and liquid electrolytes, all while maintaining adequate ionic conductivity. However, such an ideal material coating has yet to be found. Here we report a novel synthesis method by reacting clean molten lithium foil directly with pure nitrogen gas to generate instantaneously a pinhole-free and ionically conductive α-Li3N film directly bonded onto Li metal foil. The film consists of highly textured large Li3N grains (tens of μm) with (001) crystalline planes parallel to the Li metal surface. The bonding between textured grains is strong, resulting in a mechanical...

An intermediate temperature garnet-type solid electrolyte-based molten lithium battery for grid energy storage

Abstract: Batteries are an attractive grid energy storage technology, but a reliable battery system with the functionalities required for a grid such as high power capability, high safety and low cost remains elusive. Here, we report a solid electrolyte-based molten lithium battery constructed with a molten lithium anode, a molten Sn–Pb or Bi–Pb alloy cathode and a garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZTO) solid electrolyte tube. We show that the assembled Li||LLZTO||Sn–Pb and Li||LLZTO||Bi–Pb cells can stably cycle at an intermediate temperature of 240 °C for about one month at current densities of 50 mA cm−2 and 100 mA cm−2 respectively, with almost no capacity decay and an average Coulombic efficiency of 99.98%. Furthermore, the cells demonstrate high power capability with current densities up to 300 mA cm−2 (90 mW cm−2) for Li||LLZTO||Sn–Pb and 500 mA cm−2 (175 mW cm−2) for Li||LLZTO||Bi–Pb. Our design offers prospects for grid energy storage with intermediate temperature operations, high safety margin and low capital and maintenance costs.

An Aqueous Inorganic Polymer Binder for High Performance Lithium-Sulfur Batteries with Flame-Retardant Properties.

Abstract: Lithium–sulfur (Li–S) batteries are regarded as promising next-generation high energy density storage devices for both portable electronics and electric vehicles due to their high energy density, low cost, and environmental friendliness However, there remain some issues yet to be fully addressed with the main challenges stemming from the ionically insulating nature of sulfur and the dissolution of polysulfides in electrolyte with subsequent parasitic reactions leading to low sulfur utilization and poor cycle life The high flammability of sulfur is another serious safety concern which has hindered its further application Herein, an aqueous inorganic polymer, ammonium polyphosphate (APP), has been developed as a novel multifunctional binder to address the above issues The strong binding affinity of the main chain of APP with lithium polysulfides blocks diffusion of polysulfide anions and inhibits their shuttling effect The coupling of APP with Li ion facilitates ion transfer and promotes the kinetics o

Engineering stable interfaces for three-dimensional lithium metal anodes

Abstract: Lithium metal has long been considered one of the most promising anode materials for advanced lithium batteries (for example, Li-S and Li-O2), which could offer significantly improved energy density compared to state-of-the-art lithium ion batteries. Despite decades of intense research efforts, its commercialization remains limited by poor cyclability and safety concerns of lithium metal anodes. One root cause is the parasitic reaction between metallic lithium and the organic liquid electrolyte, resulting in continuous formation of an unstable solid electrolyte interphase, which consumes both active lithium and electrolyte. Until now, it has been challenging to completely shut down the parasitic reaction. We find that a thin-layer coating applied through atomic layer deposition on a hollow carbon host guides lithium deposition inside the hollow carbon sphere and simultaneously prevents electrolyte infiltration by sealing pinholes on the shell of the hollow carbon sphere. By encapsulating lithium inside the stable host, parasitic reactions are prevented, resulting in impressive cycling behavior. We report more than 500 cycles at a high coulombic efficiency of 99% in an ether-based electrolyte at a cycling rate of 0.5 mA/cm2 and a cycling capacity of 1 mAh/cm2, which is among the most stable Li anodes reported so far.

Reversible and selective ion intercalation through the top surface of few-layer MoS2

Abstract: Electrochemical intercalation of ions into the van der Waals gap of two-dimensional (2D) layered materials is a promising low-temperature synthesis strategy to tune their physical and chemical properties. It is widely believed that ions prefer intercalation into the van der Waals gap through the edges of the 2D flake, which generally causes wrinkling and distortion. Here we demonstrate that the ions can also intercalate through the top surface of few-layer MoS2 and this type of intercalation is more reversible and stable compared to the intercalation through the edges. Density functional theory calculations show that this intercalation is enabled by the existence of natural defects in exfoliated MoS2 flakes. Furthermore, we reveal that sealed-edge MoS2 allows intercalation of small alkali metal ions (e.g., Li+ and Na+) and rejects large ions (e.g., K+). These findings imply potential applications in developing functional 2D-material-based devices with high tunability and ion selectivity. Electrochemical ion intercalation in 2D layered materials is known to occur through the material’s edges, accompanied by frequent structural deformations. Here the authors show that in MoS2 flakes where the edges have been sealed, a reversible and ion-selective intercalation occurs through the top surface via the intrinsic defects.

Lithium metal stripping beneath the solid electrolyte interphase.

Abstract: Lithium stripping is a crucial process coupled with lithium deposition during the cycling of Li metal batteries. Lithium deposition has been widely studied, whereas stripping as a subsurface process has rarely been investigated. Here we reveal the fundamental mechanism of stripping on lithium by visualizing the interface between stripped lithium and the solid electrolyte interphase (SEI). We observed nanovoids formed between lithium and the SEI layer after stripping, which are attributed to the accumulation of lithium metal vacancies. High-rate dissolution of lithium causes vigorous growth and subsequent aggregation of voids, followed by the collapse of the SEI layer, i.e., pitting. We systematically measured the lithium polarization behavior during stripping and find that the lithium cation diffusion through the SEI layer is the rate-determining step. Nonuniform sites on typical lithium surfaces, such as grain boundaries and slip lines, greatly accelerated the local dissolution of lithium. The deeper understanding of this buried interface stripping process provides beneficial clues for future lithium anode and electrolyte design.