A general method to synthesize and sinter bulk ceramics in seconds

Ceramics are an important class of materials with widespread applications because of their high thermal, mechanical, and chemical stability. Computational predictions based on first principles methods can be a valuable tool in accelerating materials discovery to develop improved ceramics. It is essential to experimentally confirm the material properties of such predictions. However, materials screening rates are limited by the long processing times and the poor compositional control from volatile element loss in conventional ceramic sintering techniques. To overcome these limitations, we developed an ultrafast high-temperature sintering (UHS) process for the fabrication of ceramic materials by radiative heating under an inert atmosphere. We provide several examples of the UHS process to demonstrate its potential utility and applications, including advancements in solid-state electrolytes, multicomponent structures, and high-throughput materials screening.

Rapid, High-Temperature, In Situ Microwave Synthesis of Bulk Nanocatalysts

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.

Fly-through synthesis of nanoparticles on textile and paper substrates

The fast and efficient synthesis of nanoparticles on flexible and lightweight substrates is increasingly critical for various medical and wearable applications. However, conventional high temperature (high-T) processes for nanoparticle synthesis are intrinsically incompatible with temperature-sensitive substrates, including textiles and paper (i.e. low-T substrates). In this work, we report a non-contact, 'fly-through' method to synthesize nanoparticles on low-T substrates by rapid radiative heating under short timescales. As a demonstration, textile substrates loaded with platinum (Pt) salt precursor are rapidly heated and quenched as they move across a 2000 K heating source at a continuous production speed of 0.5 cm s-1. The rapid radiative heating method induces the thermal decomposition of various precursor salts and nanoparticle formation, while the short duration ensures negligible change to the respective low-T substrate along with greatly improved production efficiency. The reported method can be generally applied to the synthesis of metal nanoparticles (e.g. gold and ruthenium) on various low-T substrates (e.g. paper). The non-contact and continuous 'fly-through' synthesis offers a robust and efficient way to synthesize supported nanoparticles on flexible and lightweight substrates. It is also promising for ultrafast and roll-to-roll manufacturing to enable viable applications.

Nanocellulose-Enabled, All-Nanofiber, High-Performance Supercapacitor

Nanocellulose has been used as a sustainable nanomaterial for constructing advanced electrochemical energy-storage systems with renewability, lightweight, flexibility, high performance, and satisfying safety. Here, we demonstrate a high-performance all-nanofiber asymmetric supercapacitor (ASC) assembled using a forest-based, nanocellulose-derived hierarchical porous carbon (nanocellulose carbon, HPC) anode, a mesoporous nanocellulose membrane separator (nanocellulose separator), and a NiCo₂O₄ cathode with nanocellulose carbon as the support matrix (nanocellulose cathode, HPC/NiCo₂O₄). HPC has a three-dimensional porous structure comprising interconnected nanofibers with an ultrahigh surface area of 2046 m² g^-1. When integrated with the mesoporous feature of the nanocellulose membrane separator, these properties facilitate the quick delivery of both ions and electrons even with a thick (up to several hundreds of micrometers) and highly loaded (5.8 mg cm^-2) ASC design. Consequently, the all-nanofiber ASC demonstrates a high electrochemical performance (64.83 F g^-1 (10.84 F cm^-3) at 0.25 A g^-1 and 32.78 F g^-1 or 5.48 F cm^-3 at 4 A g^-1) that surpasses most cellulose-based ASCs ever reported. Moreover, the nanocellulose components promise renewability, low cost, and biodegradability, thereby presenting a promising direction toward high-power, environmentally friendly, and renewable energy-storage devices.

An Electron/Ion Dual-Conductive Alloy Framework for High-Rate and High-Capacity Solid-State Lithium-Metal Batteries

The solid-state Li battery is a promising energy-storage system that is both safe and features a high energy density. A main obstacle to its application is the poor interface contact between the solid electrodes and the ceramic electrolyte. Surface treatment methods have been proposed to improve the interface of the ceramic electrolytes, but they are generally limited to low-capacity or short-term cycling. Herein, an electron/ion dual-conductive solid framework is proposed by partially dealloying the Li-Mg alloy anode on a garnet-type solid-state electrolyte. The Li-Mg alloy framework serves as a solid electron/ion dual-conductive Li host during cell cycling, in which the Li metal can cycle as a Li-rich or Li-deficient alloy anode, free from interface deterioration or volume collapse. Thus, the capacity, current density, and cycle life of the solid Li anode are improved. The cycle capability of this solid anode is demonstrated by cycling for 500 h at 1 mA cm^-2 , followed by another 500 h at 2 mA cm^-2 without short-circuiting, realizing a record high cumulative capacity of 750 mA h cm^-2 for garnet-type all-solid-state Li batteries. This alloy framework with electron/ion dual-conductive pathways creates the possibility to realize high-energy solid-state Li batteries with extended lifespans.

Interface Engineering for Garnet-Based Solid-State Lithium-Metal Batteries: Materials, Structures, and Characterization

Lithium-metal batteries are considered one of the most promising energy-storage systems owing to their high energy density, but their practical applications have long been hindered by significant safety concerns and poor cycle stability. Solid-state electrolytes (SSEs) are expected to improve not only the safety but also the energy density of Li-metal batteries. The key challenge for solid-state Li-metal batteries lies in the low ionic conductivity of the SSEs and moreover the interface contact between the electrode and SSE. To achieve feasible solid-state Li-metal batteries, it is imperative that the ionic conductivity is improved, especially at the electrode-SSE interface. Herein, recent advances in interface engineering for solid-state Li-metal batteries are reported, mainly focusing on garnet-type SSEs. Various materials to modify the cathode-garnet and Li-garnet interfaces by intermediate layers, alloys, and polymer electrolytes are analyzed. Structural innovations for SSEs including composite electrolytes and multilayer SSE frameworks are reviewed, along with advanced characterization approaches to probe the interfaces, which will provide further insights for garnet-based solid-state batteries. Future challenges and the great promise of garnet-based Li-metal batteries are discussed to close.

Muscle-Inspired Highly Anisotropic, Strong, Ion-Conductive Hydrogels

Biological tissues generally exhibit excellent anisotropic mechanical properties owing to their well-developed microstructures. Inspired by the aligned structure in muscles, a highly anisotropic, strong, and conductive wood hydrogel is developed by fully utilizing the high-tensile strength of natural wood, and the flexibility and high-water content of hydrogels. The wood hydrogel exhibits a high-tensile strength of 36 MPa along the longitudinal direction due to the strong bonding and cross-linking between the aligned cellulose nanofibers (CNFs) in wood and the polyacrylamide (PAM) polymer. The wood hydrogel is 5 times and 500 times stronger than the bacterial cellulose hydrogels (7.2 MPa) and the unmodified PAM hydrogel (0.072 MPa), respectively, representing one of the strongest hydrogels ever reported. Due to the negatively charged aligned CNF, the wood hydrogel is also an excellent nanofluidic conduit with an ionic conductivity of up to 5 × 10^-4 S cm^-1 at low concentrations for highly selective ion transport, akin to biological muscle tissue. The work offers a promising strategy to fabricate a wide variety of strong, anisotropic, flexible, and ionically conductive wood-based hydrogels for potential biomaterials and nanofluidic applications.

Anisotropic, lightweight, strong, and super thermally insulating nanowood with naturally aligned nanocellulose

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 <5% over the solar spectrum with the ability to effectively reflect solar thermal energy. Moreover, the nanowood is lightweight yet strong, owing to the effective bonding between the aligned cellulose nanofibrils with a high compressive strength of 13 MPa in the axial direction and 20 MPa in the transverse direction at 75% strain, which exceeds other thermal insulation materials, such as silica and polymer aerogels, Styrofoam, and wool. The excellent thermal management, abundance, biodegradability, high mechanical strength, low mass density, and manufacturing scalability of the nanowood make this material highly attractive for practical thermal insulation applications.

Rapid Thermal Annealing of Cathode-Garnet Interface toward High-Temperature Solid State Batteries

High-temperature batteries require the battery components to be thermally stable and function properly at high temperatures. Conventional batteries have high-temperature safety issues such as thermal runaway, which are mainly attributed to the properties of liquid organic electrolytes such as low boiling points and high flammability. In this work, we demonstrate a truly all-solid-state high-temperature battery using a thermally stable garnet solid-state electrolyte, a lithium metal anode, and a V₂O₅ cathode, which can operate well at 100 °C. To address the high interfacial resistance between the solid electrolyte and cathode, a rapid thermal annealing method was developed to melt the cathode and form a continuous contact. The resulting interfacial resistance of the solid electrolyte and V₂O₅ cathode was significantly decreased from 2.5 × 10⁴ to 71 Ω·cm² at room temperature and from 170 to 31 Ω·cm² at 100 °C. Additionally, the diffusion resistance in the V₂O₅ cathode significantly decreased as well. The demonstrated high-temperature solid-state full cell has an interfacial resistance of 45 Ω·cm² and 97% Coulombic efficiency cycling at 100 °C. This work provides a strategy to develop high-temperature all-solid-state batteries using garnet solid electrolytes and successfully addresses the high contact resistance between the V₂O₅ cathode and garnet solid electrolyte without compromising battery safety or performance.

Inverted battery design as ion generator for interfacing with biosystems

In a lithium-ion battery, electrons are released from the anode and go through an external electronic circuit to power devices, while ions simultaneously transfer through internal ionic media to meet with electrons at the cathode. Inspired by the fundamental electrochemistry of the lithium-ion battery, we envision a cell that can generate a current of ions instead of electrons, so that ions can be used for potential applications in biosystems. Based on this concept, we report an 'electron battery' configuration in which ions travel through an external circuit to interact with the intended biosystem whereas electrons are transported internally. As a proof-of-concept, we demonstrate the application of the electron battery by stimulating a monolayer of cultured cells, which fluoresces a calcium ion wave at a controlled ionic current. Electron batteries with the capability to generate a tunable ionic current could pave the way towards precise ion-system control in a broad range of biological applications.

Garnet Solid Electrolyte Protected Li-Metal Batteries

Garnet-type solid state electrolyte (SSE) is a promising candidate for high performance lithium (Li)-metal batteries due to its good stability and high ionic conductivity. One of the main challenges for garnet solid state batteries is the poor solid-solid contact between the garnet and electrodes, which results in high interfacial resistance, large polarizations, and low efficiencies in batteries. To address this challenge, in this work gel electrolyte is used as an interlayer between solid electrolyte and solid electrodes to improve their contact and reduce their interfacial resistance. The gel electrolyte has a soft structure, high ionic conductivity, and good wettability. Through construction of the garnet/gel interlayer/electrode structure, the interfacial resistance of the garnet significantly decreased from 6.5 × 10⁴ to 248 Ω cm² for the cathode and from 1.4 × 10³ to 214 Ω cm² for the Li-metal anode, successfully demonstrating a full cell with high capacity (140 mAh/g for LiFePO₄ cathode) over 70 stable cycles in room temperature. This work provides a binary electrolyte consisting of gel electrolyte and solid electrolyte to address the interfacial challenge of solid electrolyte and electrodes and the demonstrated hybrid battery presents a promising future for battery development with high energy and good safety.

Reducing Interfacial Resistance between Garnet-Structured Solid-State Electrolyte and Li-Metal Anode by a Germanium Layer

Substantial efforts are underway to develop all-solid-state Li batteries (SSLiBs) toward high safety, high power density, and high energy density. Garnet-structured solid-state electrolyte exhibits great promise for SSLiBs owing to its high Li-ion conductivity, wide potential window, and sufficient thermal/chemical stability. A major challenge of garnet is that the contact between the garnet and the Li-metal anodes is poor due to the rigidity of the garnet, which leads to limited active sites and large interfacial resistance. This study proposes a new methodology for reducing the garnet/Li-metal interfacial resistance by depositing a thin germanium (Ge) (20 nm) layer on garnet. By applying this approach, the garnet/Li-metal interfacial resistance decreases from ≈900 to ≈115 Ω cm² due to an alloying reaction between the Li metal and the Ge. In agreement with experiments, first-principles calculation confirms the good stability and improved wetting at the interface between the lithiated Ge layer and garnet. In this way, this unique Ge modification technique enables a stable cycling performance of a full cell of lithium metal, garnet electrolyte, and LiFePO₄ cathode at room temperature.

Enabling High-Areal-Capacity Lithium-Sulfur Batteries: Designing Anisotropic and Low-Tortuosity Porous Architectures

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 also be applied to other cathode materials to achieve a high areal capacity with uncompromised rate and cycling performance.

Carbon Welding by Ultrafast Joule Heating

Carbon nanomaterials exhibit outstanding electrical and mechanical properties, but these superior properties are often compromised as nanomaterials are assembled into bulk structures. This issue of scaling limits the use of carbon nanostructures and can be attributed to poor physical contacts between nanostructures. To address this challenge, we propose a novel technique to build a 3D interconnected carbon matrix by forming covalent bonds between carbon nanostructures. High temperature Joule heating was applied to bring the carbon nanofiber (CNF) film to temperatures greater than 2500 K at a heating rate of 200 K/min to fuse together adjacent carbon nanofibers with graphitic carbon bonds, forming a 3D continuous carbon network. The bulk electrical conductivity of the carbon matrix increased four orders of magnitude to 380 S/cm with a sheet resistance of 1.75 Ω/sq. The high temperature Joule heating not only enables fast graphitization of carbon materials at high temperature, but also provides a new strategy to build covalently bonded graphitic carbon networks from amorphous carbon source. Because of the high electrical conductivity, good mechanical structures, and anticorrosion properties, the 3D interconnected carbon membrane shows promising applications in energy storage and electrocatalysis fields.