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High entropy alloy nanoparticles (HEA-NPs) are reported to have superior performance in catalysis, energy storage, and conversion due to the broad range of elements that can be incorporated in these materials, enabling tunable activity, excellent thermal and chemical stability, and a synergistic catalytic effect. However, scaling the manufacturing of HEA-NPs with uniform particle size and homogeneous elemental distribution efficiently is still a challenge due to the required critical synthetic conditions where high temperature is typically involved. In this work, we demonstrate an efficient and scalable microwave heating method using carbon-based materials as substrates to fabricate HEA-NPs with uniform particle size. Due to the abundant functional group defects that can absorb microwave efficiently, reduced graphene oxide is employed as a model substrate to produce an average temperature reaching as high as ∼1850 K within seconds. As a proof-of-concept, we utilize this rapid, high-temperature heating process to synthesize PtPdFeCoNi HEA-NPs, which exhibit an average particle size of ∼12 nm and uniform elemental mixing resulting from decomposition nearly at the same time and liquid metal solidification without diffusion. Various carbon-based materials can also be employed as substrates, including one-dimensional carbon nanofibers and three-dimensional carbonized wood, which can achieve temperatures of >1400 K. This facile and efficient microwave heating method is also compatible with the roll-to-roll process, providing a feasible route for scalable HEA-NPs manufacturing.

The use of solid-state electrolyte may be necessary to enable safe, high-energy-density Li metal anodes for next-generation energy storage systems. However, the inhomogeneous local current densities during long-term cycling result in instability and detachment of the Li anode from the electrolyte, which greatly hinders practical application. In this study, we report a new approach to maintain a stable Li metal | electrolyte interface by depositing an amorphous carbon nanocoating on garnet-type solid-state electrolyte. The carbon nanocoating provides both electron and ion conducting capability, which helps to homogenize the lithium metal stripping and plating processes. After coating, we find the Li metal/garnet interface displays stable cycling at 3 mA/cm2 for more than 500 h, demonstrating the interface's outstanding electro-chemomechanical stability. This work suggests amorphous carbon coatings may be a promising strategy for achieving stable Li metal | electrolyte interfaces and reliable Li metal batteries.

Solid-state lithium batteries using inorganic electrolytes are expected to revolutionize energy storage systems due to their better safety and high energy density. However, their application is greatly hindered by the poor solid-solid interface between the solid-state electrolyte (SSE) and electrodes, particularly the cathode. Herein, we report a facile strategy to address the high cathode/SSE interfacial resistance through rapid, high-temperature microwave soldering. As a proof-of-concept demonstration, we soldered a garnet-type Li7La3Zr2O12 (LLZO) SSE with a V2O5 cathode, which feature high thermal stability and suitable melting temperatures. Our microwave soldering technique can selectively melt the surface of the granular V2O5 and rapidly form an intact and continuous cathode layer with tightly embedded carbon black nanoparticles, leading to a remarkable 690-time increase of the electronic conductivity of cathode. Additionally, the melted V2O5 cathode is conformally soldered to the garnet electrolyte, resulting in a 28-fold decrease of the cathode/garnet interfacial resistance (from 14.4 ​kΩ ​cm2to 0.5 ​kΩ ​cm2. As a result, this all-solid-state full cell displays a low overall resistance of 0.3 ​kΩ ​cm2 at 100 ​°C, which enables stable cyclability of the battery without the addition of liquid/polymer electrolyte. The fast microwave soldering strategy constitutes a significant step towards the development of the all-solid-state batteries.

Electric conductors are ubiquitously used for electromagnetic shielding, flexible electronics, and energy storage, with metals and carbon-based compounds as traditional choices for these applicatio...

Summary Here we demonstrate a thermal shock synthesis method triggered by microwave irradiation for the rapid synthesis of nanoparticles on reduced graphene oxide (RGO) substrate. With properly controlled reduction, RGO has high electrical conductivity while maintaining functional groups, leading to an extremely efficient microwave absorption of ∼70%. The high utilization of microwaves results in the ability to raise the temperature to 1,600 K in just 100 ms, which is followed by rapid quenching to room temperature. The defects on the RGO are crucial for achieving this record-high microwave-induced temperature as these defects play a fundamental role in absorbing the radiation as well as the self-quenching mechanism. By loading precursors onto RGO, we can utilize rapid temperature change to synthesize nanoparticles. The nanoparticles are ∼10 nm with uniform distribution. This facile, rapid, and universal synthesis technique has the potential to be employed in large-scale production of nanomaterials and suggests a new direction for nanosynthesis.

High performance and low-cost electrocatalysts for overall water splitting, i.e., catalyzing hydrogen and oxygen evolution reactions with the same material, are of great importance for large-scale, renewable energy conversion processes. Here, we report an ultrafast (~ 7 ms) synthesis technique for transition metal chalcogenide nanoparticles assisted by high temperature treatment. As a proof of concept, we demonstrate that cobalt sulfide (~ 20 nm in diameter)@ few-layer graphene (~ 2 nm in thickness) core-shell nanoparticles embedded in RGO nanosheets exhibit remarkable bifunctional electrocatalytic activity and stability for overall water splitting, which is comparable to commercial 40 wt.% platinum/carbon (Pt/C) electrocatalysts. After 60 h of continuous operation, 10 mA·cm−2 water splitting current density can still be achieved at a low potential of ~ 1.77 V without any activity decay, which is among the most active for non-noble material based electrocatalysts. The presented study provides prospects in synthesizing highly efficient bifunctional electrocatalysts for large-scale energy conversion application via a simple yet efficient technique.

Li–CO2 batteries are considered promising approaches for reducing the “greenhouse effect” and taking advantage of the abundant CO2 in the atmosphere for use in energy storage devices, due to the molecule's reversible reaction with Li. However, Li–CO2 batteries suffer from several setbacks, such as poor rechargeability and low Coulombic efficiency. Designing and fabricating a highly efficient cathode is one of the key components to improving the electrochemical performance. For the first time, we demonstrate a transient, in situ thermal shock method combined with a three-dimensional cross-linked structure derived from CO2 gasification to produce a high dispersion of ultrafine Ru nanoparticles on activated carbon nanofibers to serve as an efficient cathode in Li–CO2 batteries. The interconnected channels, numerous pores, ultrafine nanoparticles, and highly crystalline structure promote the diffusion of CO2 and the permeation of electrolyte, enhancing the catalytic decomposition of discharge products in Li–CO2 batteries. These devices exhibit not only impressive cycling performance with a limited capacity of 1000 mA h g−1, but also a low overpotential due to the sufficient number of active sites on the cathode. The electrode displays a low overpotential of 1.43 V after 50 cycles at 0.1 A g−1. Furthermore, low overpotentials of 1.79 and 1.81 V can be achieved even at elevated current densities of 0.8 and 1.0 A g−1, respectively. In comparison, the previously reported overpotentials were up to 1.95 and 1.90 V at low current densities of 0.1 and 0.2 A g−1, respectively, indicating the Ru nanoparticles on the carbon nanofibers display excellent catalytic performance towards the reaction of Li and CO2. Therefore, this approach offers a new pathway to high performance Li–CO2 batteries and may spur further applications in catalysis and other renewable energy storage technologies.

Li-S batteries, while promising, face tremendous challenges due to the infinite volume change of the lithium anode, the constantly evolving solid-electrolyte interface, and the polysulfide shuttling effect. Herein we report a novel all-in-one cell design introduced by a porous-dense-porous trilayer garnet electrolyte. Both lithium anode and the sulfur cathode are infiltrated in the porous garnet framework, resulting in the first reported solid-state all-in-one battery. The interconnected 3D garnet electrolyte provides ion pathways throughout the whole cell while the conformal coating of carbon nanotubes and infiltrated lithium metal form continuous pathways for electrons. The all-in-one cell design has the following advantages: (1) continuous pathways for Li+ and electrons that lead to a lower resistance, (2) all-solid-state lithium metal anode eliminating the formation of an SEI, (3) seamless contact between the garnet and lithium metal introduced by a ZnO surface treatment that results in small interface resistance, (4) low local current density at an applied areal current density due to high contact area of the 3D porous structure, (5) locally confined volume changes for both anode and cathode, avoiding dead Li and dead S formation, (6) the use of a thin dense ceramic electrolyte as a separator enabled by the trilayer architecture, which is otherwise impossible due to inherent brittleness of thin film ceramics, (7) unique approaches for cell manufacturing and packaging made available by the all-in-one design, which bring about new opportunities. As a proof of concept, we demonstrated the all-in-one Li-S battery which completely eliminates lithium polysulfide shuttling and lithium dendrite penetration, leading to a high efficiency and safe operating battery system. With both lithium and sulfur infused in the porous layer of the solid-state electrolyte, the proposed Li-S battery achieves a high capacity of over 1200 mAh/gS and nearly 100% coulombic efficiency, demonstrating the advantages of the all-in-one design.

Solid-state electrolytes (SSEs) have been widely studied to enable applications of high-energy Li metal anodes in batteries with high safety and stable performance. However, integration of SSEs into batteries is hindered by the infinite volume change of Li metal anodes upon cycling, the unstable resistance between Li and SSE, and low battery energy densities. To address these challenges, we developed a porous-dense bilayer structured garnet SSE as a 3D ionic framework for Li metal. The framework consists of one porous layer as a volume-stable host of Li metal with a large contact area, and one dense layer as a solid-state separator preventing short-circuits. The flatness of the dense layer enables simple battery manufacturing by laying a pre-made cathode on top of the bilayer framework. The thicknesses of the porous and dense layers are well controlled at 50 and 20 µm, respectively, to improve the battery energy density. Based on the bilayer garnet framework and highly loaded Li(Ni0.5Mn0.3Co0.2)O2 (NMC) cathodes (32 mg/cm2), we developed solid-state Li-NMC batteries with energy densities (329 W h/kg and 972 W h/L) significantly higher than all of the state-of-art garnet-based Li metal batteries. The bilayer framework design provides a promising strategy towards solid-state Li metal batteries with high energy densities because of its well-optimized thickness, stable cycling performance, and feasibility to be integrated with high-energy cathodes.

Designing solid-state lithium metal batteries requires fast lithium-ion conductors, good electrochemical stability, and scalable processing approaches to device integration. In this work, we demonstrate a unique design for a flexible lithium-ion conducting ceramic textile with the above features for use in solid-state batteries. The ceramic textile was based on the garnet-type conductor Li7La3Zr2O12 and exhibited a range of desirable chemical and structural properties, including: lithium-ion conducting cubic structure, low density, multi-scale porosity, high surface area/volume ratio, and good flexibility. The solid garnet textile enabled reinforcement of a solid polymer electrolyte to achieve high lithium-ion conductivity and stable long-term Li cycling over 500 h without failure. The textile also provided an electrolyte framework when designing a 3D electrode to realize ultrahigh cathode loading (10.8 g/cm2 sulfur) for high-performance Li-metal batteries.

Solid-state electrolytes (SSEs) have been widely considered as enabling materials for the practical application of lithium metal anodes. However, many problems inhibit the widespread application of solid state batteries, including the growth of lithium dendrites, high interfacial resistance, and the inability to operate at high current density. In this study, we report a three-dimensional (3D) mixed electron/ion conducting framework (3D-MCF) based on a porous-dense-porous trilayer garnet electrolyte structure created via tape casting to facilitate the use of a 3D solid state lithium metal anode. The 3D-MCF was achieved by a conformal coating of carbon nanotubes (CNTs) on the porous garnet structure, creating a composite mixed electron/ion conductor that acts as a 3D host for the lithium metal. The lithium metal was introduced into the 3D-MCF via slow electrochemical deposition, forming a 3D lithium metal anode. The slow lithiation leads to improved contact between the lithium metal anode and garnet electrolyte, resulting in a low resistance of 25 Ω cm

The interaction between metal nanoparticles (NPs) and their substrate plays a critical role in determining the particle morphology, distribution, and properties. The pronounced impact of a thin oxide coating on the dispersion of metal NPs on a carbon substrate is presented. Al2 O3 -supported Pt NPs are compared to the direct synthesis of Pt NPs on bare carbon surfaces. Pt NPs with an average size of about 2 nm and a size distribution ranging between 0.5 nm and 4.0 nm are synthesized on the Al2 O3 coated carbon nanofiber, a significant improvement compared to those directly synthesized on a bare carbon surface. First-principles modeling verifies the stronger adsorption of Pt clusters on Al2 O3 than on carbon, which attributes the formation of ultrafine Pt NPs. This strategy paves the way towards the rational design of NPs with enhanced dispersion and controlled particle size, which are promising in energy storage and electrocatalysis.

Carbon dioxide is understood as a major contributor to the greenhouse effect. The search for an effective and efficient method for CO2 capture and utilization has become a priority task on a global scale. For Mars exploration missions, the ability to use the CO2 in the atmosphere (96%) could offer great benefits in terms of energy storage. The Li–CO2 battery is considered a promising platform for CO2 capture, with its ability to utilize the captured CO2 for energy storage. However, the Li–CO2 battery still suffers various inadequacies, including the slow kinetics of CO2 reduction, the high charge/discharge hysteresis, the ultra-stable discharge product, and the slow transport of CO2 gas and electrolyte. In this work, we introduce a high-capacity, long-life Li–CO2 battery based on a flexible wood cathode architecture. Mother nature has produced the most efficient ion and gas transport architectural system in the form of wood. The unique channel structure of the wood-based cathode separates the transport of CO2 and the electrolyte into specific pathways, leading to facilitated transport. The improvements in mass transport, combined with faster kinetics as a result of the use of Ru nanocatalyst supported on carbon nanotubes that reside in the microchannels, contribute to substantially improved electrochemical performance. Stable cycling for over 200 cycles with both a low overpotential and an ultrahigh discharge capacity of 11 mA h cm−2 is achieved with the flexible wood-based Li–CO2 battery. Such a long cycle life and high capacity is unprecedented for a Li–CO2 battery. Additionally, the cathode exhibits excellent mechanical flexibility imparted by the flexible wood scaffold, holding great promise for wearable device applications. The high capacity and the long cycle life make the flexible wood cathode Li–CO2 battery a promising candidate for combining CO2 capture and utilization.

Room-temperature Na ion batteries (NIBs) have attracted great attention because of the widely available, abundant sodium resources and potentially low cost. Currently, the challenge of the NIB development is due primarily to the lack of a high-performance anode, while the Na metal anode holds great promise considering its highest specific capacity of 1165 mA h/g and lowest anodic potential. However, an uneven deposit, relatively infinite volume change, and dendritic growth upon plating/stripping cycles cause a low Coulombic efficiency, poor cycling performance, and severe safety concerns. Here, a stable Na carbonized wood (Na-wood) composite anode was fabricated via a rapid melt infusion (about 5 s) into channels of carbonized wood by capillary action. The channels function as a high-surface-area, conductive, mechanically stable skeleton, which lowers the effective current density, ensures a uniform Na nucleation, and restricts the volume change over cycles. As a result, the Na-wood composite anode exhibited flat plating/stripping profiles with smaller overpotentials and stable cycling performance over 500 h at 1.0 mA/cm

Nanoparticles (NPs) dispersed within a conductive host are essential for a range of applications including electrochemical energy storage, catalysis, and energetic devices. However, manufacturing high quality NPs in an efficient manner remains a challenge, especially due to agglomeration during assembly processes. Here we report a rapid thermal shock method to in situ synthesize well-dispersed NPs on a conductive fiber matrix using metal precursor salts. The temperature of the carbon nanofibers (CNFs) coated with metal salts was ramped from room temperature to ∼2000 K in 5 ms, which corresponds to a rate of 400,000 K/s. Metal salts decompose rapidly at such high temperatures and nucleate into metallic nanoparticles during the rapid cooling step (cooling rate of ∼100,000 K/s). The high temperature duration plays a critical role in the size and distribution of the nanoparticles: the faster the process is, the smaller the nanoparticles are, and the narrower the size distribution is. We also demonstrated that the peak temperature of thermal shock can reach ∼3000 K, much higher than the decomposition temperature of many salts, which ensures the possibility of synthesizing various types of nanoparticles. This universal, in situ, high temperature thermal shock method offers considerable potential for the bulk synthesis of unagglomerated nanoparticles stabilized within a matrix., Uniformly small, well-dispersed nanoparticles on a conductive matrix were synthesized by a rapid thermal shock method (2100 K, 5 ms), showing a new way for ultrafast and energy efficient nanoparticle dispersal by high temperature shock.

Lithium metal anode with the highest capacity and lowest anode potential is extremely attractive to battery technologies, but infinite volume change during the Li stripping/plating process results in cracks and fractures of the solid electrolyte interphase, low Coulombic efficiency, and dendritic growth of Li. Here, we use a carbonized wood (C-wood) as a 3D, highly porous (73% porosity) conductive framework with well-aligned channels as Li host material. We discovered that molten Li metal can infuse into the straight channels of C-wood to form a Li/C-wood electrode after surface treatment. The C-wood channels function as excellent guides in which the Li stripping/plating process can take place and effectively confine the volume change that occurs. Moreover, the local current density can be minimized due to the 3D C-wood framework. Therefore, in symmetric cells, the as-prepared Li/C-wood electrode presents a lower overpotential (90 mV at 3 mA⋅cm-2), more-stable stripping/plating profiles, and better cycling performance (∼150 h at 3 mA⋅cm-2) compared with bare Li metal electrode. Our findings may open up a solution for fabricating stable Li metal anode, which further facilitates future application of high-energy-density Li metal batteries.

To simultaneously address the challenges of chemical/physical short circuits and electrode volume variation, we demonstrate a three-dimensional (3D) bilayer garnet solid-state electrolyte framework for advanced Li metal batteries. The dense layer is reduced in thickness to a few microns and still retains good mechanical stability, thereby enabling the safe use of Li metal anodes. The thick porous layer acts as a mechanical support for the thin dense layer which serves as a host for high loading of cathode materials and provides pathways for continuous ion transport. Results show that the integrated sulfur cathode loading can reach >7 mg cm−2 while the proposed hybrid Li–S battery exhibits a high initial coulombic efficiency (>99.8%) and high average coulombic efficiency (>99%) during the subsequent cycles. This electrolyte framework represents a promising strategy to revolutionize Li-metal batteries by transitioning to all-solid-state batteries and can be extended to other cathode materials.

Solid-state electrolytes are known for nonflammability, dendrite blocking, and stability over large potential windows. Garnet-based solid-state electrolytes have attracted much attention for their high ionic conductivities and stability with lithium metal anodes. However, high-interface resistance with lithium anodes hinders their application to lithium metal batteries. Here, we demonstrate an ultrathin, conformal ZnO surface coating by atomic layer deposition for improved wettability of garnet solid-state electrolytes to molten lithium that significantly decreases the interface resistance to as low as ∼20 Ω·cm2. The ZnO coating demonstrates a high reactivity with lithium metal, which is systematically characterized. As a proof-of-concept, we successfully infiltrated lithium metal into porous garnet electrolyte, which can potentially serve as a self-supported lithium metal composite anode having both high ionic and electrical conductivity for solid-state lithium metal batteries. The facile surface treatme...

Carbon-black-supported nanoparticles (CNPs) have attracted considerable attention for their intriguing catalytic properties and promising applications. The traditional liquid synthesis of CNPs commonly involves demanding operation conditions and complex pre- or post-treatments, which are time consuming and energy inefficient. Herein, a rapid, scalable, and universal strategy is reported to synthesize highly dispersed metal nanoparticles embedded in a carbon matrix via microwave irradiation of carbon black with preloaded precursors. By optimizing the amount of carbon black, the microwave absorption is dramatically improved while the thermal dissipation is effectively controlled, leading to a rapid temperature increase in carbon black, ramping to 1270 K in just 6 s. The whole synthesis process requires no capping agents or surfactants, nor tedious pre- or post-treatments of carbon black, showing tremendous potential for mass production. As a proof of concept, the synthesis of ultrafine Ru nanoparticles (≈2.57 nm) uniformly embedded in carbon black using this microwave heating technique is demonstrated, which displays remarkable electrocatalytic performance when used as the cathode in a Li-O2 battery. This microwave heating method can be extended to the synthesis of other nanoparticles, thereby providing a general methodology for the mass production of carbon-supported catalytic nanoparticles.

Electrochemical cells that utilize metals in the anode and an ambient gas as the active material in the cathode blur the lines between fuel cells and batteries. Such cells are under active consideration worldwide because they are considered among the most promising energy storage platforms for electrified transportation. Li-air batteries are among the most actively investigated cells in this class, but long-term challenges, such as CO2 contamination of the cathode gas and electrolyte decomposition, are associated with loss of rechargeability owing to metal carbonate formation in the cathode. Remediation of the first of these problems adds significant infrastructure burdens to the Li-air cell that bring into question its commercial viability. Several recent studies offer contradictory evidence, namely, that the presence of substantial fractions of CO2 in the cathode gas stream can have significant benefits, including increasing the already high specific energy of a Li-O2 cell by as much as 200 %. In this report, we consider electrochemical processes in model Na-O2 /CO2 cells and find that, provided the electrode/electrolyte interfaces are electrochemically stable, such cells are able to deliver both exceptional energy storage capacity and stable long-term charge-discharge cycling behaviors at room temperature.

Garnet-based solid-state Li metal batteries have been widely considered one of the most promising next-generation energy storage systems. However, the performance of these batteries is plagued by various limitations caused by the solid-state electrolyte (SSE). The poor wetting of lithium on the garnet surface diminishes the contact between the anode and electrolyte, leading to extremely high anode interfacial resistance. Similarly, the point-to-point contact between the cathode and electrolyte leads to high impedance on the cathode side. Moreover, although the SSE serves a firm barrier separating the anode and cathode, lithium dendrites can still grow through, causing a short circuit. Finally, the solid/solid interface cannot be well maintained under cycling at high current density and capacity. Recently, remarkable progress has been achieved in garnet electrolyte to resolve these problems towards the aim of a high-performance solid-state Li metal battery. In this perspective, we highlight various recent advances in the field of garnet-based solid-state battery, including improving the anode/electrolyte interface, lithium dendrite detection, reducing cathode impedance, and electrolyte architecture design.

The increasing demands for efficient and clean energy-storage systems have spurred the development of Li metal batteries, which possess attractively high energy densities. For practical application of Li metal batteries, it is vital to resolve the intrinsic problems of Li metal anodes, i.e., the formation of Li dendrites, interfacial instability, and huge volume changes during cycling. Utilization of solid-state electrolytes for Li metal anodes is a promising approach to address those issues. In this study, we use a 3D garnet-type ion-conductive framework as a host for the Li metal anode and study the plating and stripping behaviors of the Li metal anode within the solid ion-conductive host. We show that with a solid-state ion-conductive framework and a planar current collector at the bottom, Li is plated from the bottom and rises during deposition, away from the separator layer and free from electrolyte penetration and short circuit. Owing to the solid-state deposition property, Li grows smoothly in the pores of the garnet host without forming Li dendrites. The dendrite-free deposition and continuous rise/fall of Li metal during plating/stripping in the 3D ion-conductive host promise a safe and durable Li metal anode. The solid-state Li anode shows stable cycling at 0.5 mA cm-2 for 300 h with a small overpotential, showing a significant improvement compared with reported Li anodes with ceramic electrolytes. By fundamentally eliminating the dendrite issue, the solid Li metal anode shows a great potential to build safe and reliable Li metal batteries.

We report on electrochemical properties of Li/Li1.2Ni0.15Co0.1Mn0.55O2 secondary batteries in electrolytes designed to stabilize electrodeposition of lithium. Ethylene carbonate (EC): dimethyl carbonate (DMC) containing a LiPF6/LiF salt blend stabilizes lithium electrodeposition and enables Li/Li1.2Ni0.15Co0.1Mn0.55O2 batteries with a high discharge capacity of 270 mAh·g−1 at 0.05 mA cm−2. Cells containing the LiF-reinforced electrolytes also exhibit excellent capacity retention over 500 cycles with Columbic efficiencies approaching 100%. Post-mortem SEM analysis of the lithium anode shows more compact deposition in the presence of the LiF salt additive, while XPS depth profile analysis of cathodes show a more uniform distribution of Mn over the first 180 nm from the electrode/electrolyte interface. The results imply that LiF reinforced electrolytes simultaneously facilitate stable lithium electrodeposition and reduce Mn dissolution. Keywords: Lithium-ion battery, High voltage cathode, Lithium fluoride

Metal–air batteries, especially lithium and sodium air technologies, have attracted significant research attention in the past decade. The high theoretical specific energy (3500 Wh kg−1 for Li–O2 and 1600 Wh kg−1 for Na–O2) and moderate equilibrium potential (2.96 V for Li–O2 and 2.3 V for Na–O2) make these chemistries attractive energy storage platforms for transportation, autonomous aircraft, and emergent robotics technologies. The term metal–air battery, however, hardly describes the cell design under most active investigation by researchers; in most studies, O2 is used in place of air as the active material in the battery cathode. This change, designed to eliminate the formation of electrochemically stable metal hydroxide and metal carbonate discharge products when CO2 and moisture present in ambient air react with metal ions in the cathode, introduces significant new complications for practical metal–air battery design and operation that largely defeat the competitive advantages of this storage technology. Recent work has shown that when a mixture of O2 and CO2 is used as the active material in the cathode, it is possible to recharge a metal–O2/CO2 cell provided steps are taken to prevent electrolyte decomposition during recharge. In this highlight, we critically review the literature on metal–O2/CO2 cells, focusing on how the presence of CO2 in the active cathode material changes electrochemistry at the cathode and rechargeability of the cells. We also assess the progress and future prospects for metal–air battery technologies involving ambient air as the cathode gas.

Researchers transformed natural wood into a super thermal insulation structural material with aligned cellulose nanofibers., There has been a growing interest in thermal management materials due to the prevailing energy challenges and unfulfilled needs for thermal insulation applications. We demonstrate the exceptional thermal management capabilities of a large-scale, hierarchal alignment of cellulose nanofibrils directly fabricated from wood, hereafter referred to as nanowood. Nanowood exhibits anisotropic thermal properties with an extremely low thermal conductivity of 0.03 W/m·K in the transverse direction (perpendicular to the nanofibrils) and approximately two times higher thermal conductivity of 0.06 W/m·K in the axial direction due to the hierarchically aligned nanofibrils within the highly porous backbone. The anisotropy of the thermal conductivity enables efficient thermal dissipation along the axial direction, thereby preventing local overheating on the illuminated side while yielding improved thermal insulation along the backside that cannot be obtained with isotropic thermal insulators. The nanowood also shows a low emissivity of

A highly porous 2D nanomaterial, holey graphene oxide (hGO), is synthesized directly from holey graphene powder and employed to create an aqueous 3D printable ink without the use of additives or binders. Stable dispersions of hydrophilic hGO sheets in water (≈100 mg mL-1 ) can be readily achieved. The shear-thinning behavior of the aqueous hGO ink enables extrusion-based printing of fine filaments into complex 3D architectures, such as stacked mesh structures, on arbitrary substrates. The freestanding 3D printed hGO meshes exhibit trimodal porosity: nanoscale (4-25 nm through-holes on hGO sheets), microscale (tens of micrometer-sized pores introduced by lyophilization), and macroscale (

The synthesis of nanoscale metal compound catalysts has attracted much research attention in the past decade. The challenges of preparation of the metal compound include the complexity of the synthesis process and difficulty of precise control of the reaction conditions. Herein, we report an in situ synthesis of nanoparticles via a high-temperature pulse method where the bulk material acts as the precursor. During the process of rapid heating and cooling, swift melting, anchoring, and recrystallization occur, resulting in the generation of high-purity nanoparticles. In our work, the cobalt boride (Co2B) nanoparticles with a diameter of 10–20 nm uniformly anchored on the reduced graphene oxide (rGO) nanosheets were successfully prepared using the high temperature pulse method. The as-prepared Co2B/rGO composite displayed remarkable electrocatalytic performance for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). We also prepared molybdenum disulfide (MoS2) and cobalt oxide (Co3O4)...

Lithium–sulfur (Li–S) batteries have attracted much attention due to their high theoretical energy density in comparison to conventional state-of-the-art lithium-ion batteries. However, low sulfur mass loading in the cathode results in low areal capacity and impedes the practical use of Li–S cells. Inspired by wood, a cathode architecture with natural, three-dimensionally (3D) aligned microchannels filled with reduced graphene oxide (RGO) were developed as an ideal structure for high sulfur mass loading. Compared with other carbon materials, the 3D porous carbon matrix has several advantages including low tortuosity, high electrical conductivity, and good structural stability, which make it an excellent 3D lightweight current collector. The Li–S battery assembled with the wood-based sulfur electrode can deliver a high areal capacity of 15.2 mAh cm–2 with a sulfur mass loading of 21.3 mg cm–2. This work provides a facile but effective strategy to develop 3D porous electrodes for Li–S batteries, which can a...

As an anode material for lithium-ion batteries (LIBs), silicon offers among the highest theoretical storage capacity, but is known to suffer from large structural changes and capacity fading during electrochemical cycling. Nanocomposites of silicon with carbon provide a potential material platform for resolving this problem. We report a spray-pyrolysis approach for synthesizing amorphous silicon–carbon nanocomposites from organic silane precursors. Elemental mapping shows that the amorphous silicon is uniformly dispersed in the carbon matrix. When evaluated as anode materials in LIBs, the materials exhibit highly, stable performance and excellent Coulombic efficiency for more than 150 charge discharge cycles at a charging rate of 1 A/g. Post-mortem analysis indicates that the structure of the Si–C composite is retained after extended electrochemical cycling, confirming the hypothesis that better mechanical buffering is obtained when amorphous Si is embedded in a carbon matrix. Keywords: Silicon anodes, Silicon–carbon nanocomposites, Lithium ion battery

Metal–air batteries, especially lithium and sodium air technologies, have attracted significant research attention in the past decade. The high theoretical specific energy (3500 Wh kg−1 for Li–O2 and 1600 Wh kg−1 for Na–O2) and moderate equilibrium potential (2.96 V for Li–O2 and 2.3 V for Na–O2) make these chemistries attractive energy storage platforms for transportation, autonomous aircraft, and emergent robotics technologies. The term metal–air battery, however, hardly describes the cell design under most active investigation by researchers; in most studies, O2 is used in place of air as the active material in the battery cathode. This change, designed to eliminate the formation of electrochemically stable metal hydroxide and metal carbonate discharge products when CO2 and moisture present in ambient air react with metal ions in the cathode, introduces significant new complications for practical metal–air battery design and operation that largely defeat the competitive advantages of this storage technology. Recent work has shown that when a mixture of O2 and CO2 is used as the active material in the cathode, it is possible to recharge a metal–O2/CO2 cell provided steps are taken to prevent electrolyte decomposition during recharge. In this highlight, we critically review the literature on metal–O2/CO2 cells, focusing on how the presence of CO2 in the active cathode material changes electrochemistry at the cathode and rechargeability of the cells. We also assess the progress and future prospects for metal–air battery technologies involving ambient air as the cathode gas.

Multicomponent nanomaterials are extremely difficult to synthesize by conventional methods. Accordingly, nanoparticles composed of immiscible elemental combinations tend to phase-separate rather than form singe-phase solid solutions, which limits the compositional space. A synthetic technique that facilitates kinetic control over thermodynamic mixing regimes is therefore advantageous and offers untold scientific and technological opportunities. Here, we present a general route to alloy up to eight dissimilar elements into high entropy alloy nanoparticles (HEA-NPs) through a facile and tunable synthesis method: carbothermal shock (CTS).1 CTS employs flash heating and cooling of metal precursors on carbon to produce multimetallic nanoparticles with tailored elemental compositions, particle sizes, and structural complexity. Uniform mixing of nearly any metallic combination is achieved through high temperature exposure (~2000 K) during the thermal shock (55 ms) process, while rapid quenching (~105 K/s) retains this high-entropy state to form single-phase solid solutions. This new synthetic technique promotes materials discovery and design for a wide range of applications, including catalysis and energy storage. Inspired by the performance of quinary HEA-NPs as ammonia oxidation catalysts, novel solid solution nanoparticles (with 2 or more metallic elements) are synthesized and evaluated as electrocatalysts in air-based batteries, such as lithium-oxygen (Li-O2) and Li-CO2. In this way, HEA-NPs composed of catalytically active elements may impart synergistic electrocatalytic effects to improve overall battery performance. This talk will describe the process and underlying mechanism to synthesize HEA-NPs, the overall capabilities of the CTS method, and recent results on electrocatalyst development towards Li-air battery applications. References: Y Yao*, Z Huang*, P Xie*, SD Lacey*, RJ Jacob, H Xie, F Chen, A Nie, T Pu, M Rehwoldt, D Yu, MR Zachariah, C Wang, R Shahbazian-Yassar, J Lu and L Hu, “Carbothermal shock synthesis of high-entropy-alloy nanoparticles,” Science, 359 (6383), pp. 1489-1494 (2018).

Solid-state batteries have many enticing advantages in terms of safety and stability, but the solid electrolytes upon which these batteries are based typically lead to high cell resistance. Both components of the resistance (interfacial, due to poor contact with electrolytes, and bulk, due to a thick electrolyte) are a result of the rudimentary manufacturing capabilities that exist for solid-state electrolytes. In general, solid electrolytes are studied as flat pellets with planar interfaces, which minimizes interfacial contact area. Here, multiple ink formulations are developed that enable 3D printing of unique solid electrolyte microstructures with varying properties. These inks are used to 3D-print a variety of patterns, which are then sintered to reveal thin, nonplanar, intricate architectures composed only of Li7 La3 Zr2 O12 solid electrolyte. Using these 3D-printing ink formulations to further study and optimize electrolyte structure could lead to solid-state batteries with dramatically lower full cell resistance and higher energy and power density. In addition, the reported ink compositions could be used as a model recipe for other solid electrolyte or ceramic inks, perhaps enabling 3D printing in related fields.

In this work, a hierarchically porous and ultrathick “breathable” wood-based cathode for high-performance Li-O2 batteries is developed. The 3D carbon matrix obtained from the carbonized and activated wood (denoted as CA-wood) serves as a superconductive current collector and an ideal porous host for accommodating catalysts. The ruthenium (Ru) nanoparticles are uniformly anchored on the porous wall of the aligned microchannels (denoted as CA-wood/Ru). The aligned open microchannels inside the carbon matrix contribute to unimpeded oxygen gas diffusion. Moreover, the hierarchical pores on the microchannel walls can be facilely impregnated by electrolyte, forming a continuous supply of electrolyte. As a result, numerous ideal triphase active sites are formed where electrolyte, oxygen, and catalyst accumulate on the porous walls of microchannels. Benefiting from the numerous well-balanced triple-phase active sites, the assembled Li-O2 battery with the CA-wood/Ru cathode (thickness: ≈700 µm) shows a high specific area capacity of 8.58 mA h cm−2 at 0.1 mA cm−2. Moreover, the areal capacity can be further increased to 56.0 mA h cm−2 by using an ultrathick CA-wood/Ru cathode with a thickness of ≈3.4 mm. The facile ultrathick wood-based cathodes can be applied to other cathodes to achieve a super high areal capacity without sacrificing the electrochemical performance.

As demands on battery technology approach the limits of standard organic liquid electrolytes, a multitude of new materials are being developed as potential replacements, including solid-state Li-conducting ceramics. However, the major obstacles to integrating solid electrolytes into Li-ion batteries originate primarily from the relatively low ionic conductivity of the electrolyte itself (compared to organic liquid electrolytes) and from the high interfacial impedance associated with poor electrolyte-electrode contact. Several solid electrolytes, including the garnet-like ceramic Li7La3Zr2O12 (LLZ), have partially addressed the first issue by achieving ionic conductivities of ~1 mS/cm, approaching that of organic liquid electrolytes. With regards to high interfacial impedance, surface chemistry modifications at the electrolyte-electrode interface have greatly improved solid-solid contact with lithium metal anodes, though cathode interfaces remain a significant challenge for solid-state batteries. An especially promising development replaces the typical pellet geometry with a variable-porosity multi-layer structure, resulting in dramatically increased electrolyte-electrode interfacial area, thus decreasing interfacial impedance. Such an approach opens the possibility of tailoring the architecture of the electrolyte microstructure to improve the electrolyte-electrode interface and all-solid battery performance. However, what constitutes the ideal microstructure is currently unknown. At the same time, adopting such a complex structure may introduce unforeseen effects that impact overall electrolyte properties, positively or negatively. Li-ion migration through tortuous electrolyte pathways, cycling of electrode material at varying distances from the electrolyte dense layer, and effective pore filling by the electrodes are some of the new variables that must be accounted for when designing and evaluating such structures. While research on non-planar solid electrolytes exists, the focus has been limited to thin film batteries, with little work undertaken for macro-scale systems. Here, we have varied the porosity of high dimension (>100 um thick) LLZ electrolyte porous-dense-porous multi-layers, characterized the physical microstructure of the layers, and investigated how key structural parameters (e.g., tortuosity, LLZ/pore volume fractions, MAZO angle) related to the electrochemical properties. To study the LLZ microstructure, we utilized focused ion beam (FIB) tomography to reconstruct 3D representations of regions in the electrolyte, from which structural parameters were calculated. Samples to be analyzed were epoxy infiltrated and mounted in a Xenon-plasma source FIB/SEM, where we deposited platinum on the area of interest and milled a trench around the area to expose a cross-section of the LLZ (Figure 1, top). We then moved the sample to a Gallium-ion source FIB/SEM to finish polishing the cross-section (Figure 1, bottom), followed by serial milling-and-imaging to produce the set of images necessary for 3D reconstruction. To evaluate electrolyte performance, we relied on electrochemical impedance spectroscopy (EIS) to determine Li-ion conductivities for the different LLZ multi-layer microstructures. References: 1. Han, X. et al. Negating Interfacial Impedance in Garnet-based Solid-State Li Metal Batteries. Nat. Mater. 1, (2016). Figure 1

Lithium sulfur (Li-S) battery has been considered as one of the most promising next generation energy storage devices, especially for the emerging electric vehicles.1 Unlike the state-of-art lithium ion (Li-ion) batteries, the Li-S battery is based on the conversion reaction between lithium and sulfur instead of lithium intercalation/deintercalation mechanism, which leads to an exceptionally high theoretical energy density of over 500 Wh/kg.1 Despite the high energy density, there are still many problems to tackle for the application of Li-S battery. One of the biggest problems is the polysulfide shuttling effect. Massive improvements have been achieved recently to resolve the shuttling effect. However, since most methods are employed in conventional Li-S batteries, where liquid electrolyte is used, there is always dissolution of Li2Sxin the battery, leading to the decay of performance upon long term operation. Solid state electrolyte has attracted massive research attention recently due to their ability to block lithium dendrite growth and sustain safe operation. Garnet type LLCZN electrolyte has shown excellent performance due to its high ionic conductivity and stability.2-3 The nature of ceramic electrolyte can prevent the lithium polysulfide from reaching anode side, thus eliminating the polysulfude shuttling. Therefore, a solid state Li-S battery based on garnet electrolyte which can completely resolve the polysulfide shuttling problem can be a crucial step towards the actual application of Li-S battery. In this study, we introduce a solid-state Li-S battery based on a triple layer garnet type ceramic electrolyte, where a thin dense layer of garnet was sandwiched by two porous layer. Lithium and sulfur are molten infiltrated into the different porous sides of the garnet electrolyte and are separated by the dense layer of garnet. Therefore, it is impossible for Li2Sxto migrate to from the cathode to the sulfide, thus completely eliminating the shuttling effect. The proposed quasi solid state Li-S battery promotes a new design for high energy Li-S batteries. The tri-layer garnet structure was prepared via a tape casting technique. The dense layer is 30 µm thick while both the porous layers are 70 µm thick with a porosity of ~67%. The sintered trilayer was characterized via SEM, XRD and XPS. The product shows characteristic cubic garnet phase which ensures high ionic conductivity. The lithium can be stripped from one side of the other, thus enabling the operation of solid-state Li-S battery. The solid-state Li-S battery based on tri-layer garnet show high capacity of 1200 mAh/gsulfur and stable coulombic efficiency of nearly 100% after 50 cycles. Moreover, even with the extra weight introduce by the ceramic garnet electrolyte, the Li-S cell still delivered an impressive energy density of 250 Wh/kgcell. Such a high energy density makes the tri-layer Li-S battery superior compared to state-of-art Li-ion batteries. Moreover, the utilization of the solid-state electrolyte also prevents the growth of lithium dendrite, enabling a much safer battery operation. As far as we know, this is the first time a high energy density Li-S battery with all solid-state anode framework is developed. The high energy density, all-in-one configuration, solid-state Li-S battery introduces a new route for future energy storage system. Refrence P. G. Bruce et al., Nature Materials, 2012, 11, 19–29 V. Thangadurai et al., Chem. Soc. Rev., 2014, 43, 4714-4727 F. Han et al., Adv. Energy Mater. 2016, 6, 1501590

Developing low-cost, highly efficient, and robust earth-abundant electrocatalysts for hydrogen evolution reaction (HER) is critical for the scalable production of clean and sustainable hydrogen fuel through electrochemical water splitting. This study presents a facile approach for the synthesis of nanostructured pyrite-phase transition metal dichalcogenides as highly active, earth-abundant catalysts in electrochemical hydrogen production. Iron disulfide (FeS2) nanoparticles are in situ loaded and stabilized on reduced graphene oxide (RGO) through a current-induced high-temperature rapid thermal shock (≈12 ms) of crushed iron pyrite powder. FeS2 nanoparticles embedded in between RGO exhibit remarkably improved electrocatalytic performance for HER, achieving 10 mA cm−2 current at an overpotential as low as 139 mV versus a reversible hydrogen electrode with outstanding long-term stability under acidic conditions. The presented strategy for the design and synthesis of highly active earth-abundant nanomaterial catalysts paves the way for low-cost and large-scale electrochemical energy applications.