Fast-Charging, Binder-Free Lithium Battery Cathodes Enabled via Multidimensional Conductive Networks

To meet the growing demands in both energy and power densities of lithium ion batteries, electrode structures must be capable of facile electron and ion transport while minimizing the content of electrochemically inactive components. Herein, binder-free LiFePO4 (LFP) cathodes are fabricated with a multidimensional conductive architecture that allows for fast-charging capability, reaching a specific capacity of 94 mAh g-1 at 4 C. Such multidimensional networks consist of active material particles wrapped by 1D single-walled carbon nanotubes (CNTs) and bound together using 2D MXene (Ti3C2Tx) nanosheets. The CNTs form a porous coating layer and improve local electron transport across the LFP surface, while the Ti3C2Tx nanosheets provide simultaneously high electrode integrity and conductive pathways through the bulk of the electrode. This work highlights the ability of multidimensional conductive fillers to realize simultaneously superior electrochemical and mechanical properties, providing useful insights into future fast-charging electrode designs for scalable electrochemical systems.

Enhancing the Ignition and Combustion Performances of Solid Propellants Incorporating Al Particles Inside Oxidizers

The combustion efficiency of Al plays a critical role in the combustion of high-energy aluminum-based solid propellants. For traditional formulations, the Al powders are dispersed in the binder matrix, leading to limited contact with the oxidizers and hence usually insufficient combustion and higher values of the pressure exponent. In this paper, various core-shell structural Al/oxidizer composites such as Al@HMX, Al@AP, and AP@Al have been prepared by a spray-drying technique based on which solid propellants with precise interfacial control between Al particles and oxidizers were realized. Compared to the control sample, the modified propellants have a greater heat of explosion of 5890 J g-1 (15% higher) and a reduced ignition delay time of 58 ms (65% decrease). Without changing the content of components, the burn rates of propellants can be easily modulated by tuning the interfacial contact of Al and oxidizers, where it varies in a wide range of 4.56-5.79 mm s-1 at the same pressure of 1 MPa. After introducing Al/oxidizer composites, the lowest pressure exponent of 0.19 within 1-15 MPa could be achieved by using Al@HMX and AP@Al composites. The agglomeration of Al was also inhibited by using Al/oxidizer composites, and the mechanism can be interpreted by using a classical "pocket" model. Moreover, the improved combustion efficiency of the solid propellants was verified by a noticeable reduction in the unreacted Al content.

Solid State Zinc and Aluminum ion batteries: Challenges and Opportunities

Solid-state zinc ion batteries (ZIBs) and aluminum-ion batteries (AIBs) are deemed as promising candidates for supplying power in wearable devices due to merits of low cost, high safety, and tunable flexibility. However, their wide-scale practical application is limited by various challenges, down to the material level. This Review begins with elaboration of the root causes and their detrimental effect for four main limitations: electrode-electrolyte interface contact, electrolyte ionic conductivity, mechanical strength, and electrochemical stability window of the electrolyte. Thereafter, various strategies to mitigate each of the described limitation are discussed along with future research direction perspectives. Finally, to estimate the viability of these technologies for wearable applications, economic-performance metrics are compared against Li-ion batteries.

Synergistic Defect Engineering and Interface Stability of Activated Carbon Nanotubes Enabling Ultralong Lifespan All-Solid-State Lithium-Sulfur Batteries

Due to the high energy density, high safety, and low cost of sulfur, all-solid-state lithium-sulfur batteries (ASSLSBs) are considered one of the most promising next-generation energy storage devices. Nevertheless, the insufficient interfacial contact between solid electrolytes (SEs) and the active material of sulfur leads to inadequate electronic and ionic conduction, which increases interfacial resistance and capacity decay. In this paper, commercial carbon nanotubes (CNTs) are activated to form porous-CNTs (P-CNTs), which are used as sulfur-bearing matrix, forming S@P-CNTs-based composite cathodes for ASSLSBs. Compared with CNTs, P-CNTs possess a larger specific surface area and more oxygen-containing groups, providing enhanced interfacial contact and stability between S@P-CNTs and Li6PS5Cl SE, which are confirmed by scanning electron microscopy, X-ray photoelectron spectroscopy, and density functional theory calculations. Moreover, P-CNTs can form a 3D conductive network in the composite cathodes, facilitating the migration of electrons and the diffusion of ions, as well as improving the utilization of sulfur. As a result, the S@P-CNTs-based ASSLSBs display excellent electrochemical performances, especially rarely reported ultralong lifespan, which deliver a capacity of 1099.2 mA h g-1 at a current density of 1.34 mA cm-2, and remarkably maintain 70.4% of the initial capacity over 1400 cycles.

Enhanced Contact Performance and Thermal Tolerance of Ni/Bi2Te3 Joints for Bi2Te3-Based Thermoelectric Devices

Ni metal has been widely used as a barrier layer in Bi₂Te₃-based thermoelectric devices, which establishes stable joints to link Bi₂Te₃-based legs and electrodes. However, the Ni/Bi₂Te₃ joints become very fragile when the devices were exposed to high temperature, causing severe performance deterioration and even device failure. Herein, stable Ni/Bi₂Te₃ joints have been established by arc spraying of the Ni barrier layer on the Bi₂Te₃-based alloys. The interface microstructure and contact performance including the bonding strength and contact resistivity of the arc-sprayed Ni/Bi₂Te₃ joints are investigated. The results indicate that, as compared with traditional Ni/Bi₂Te₃ joints, the arc-sprayed Ni/Bi₂Te₃ joints have comparably low contact resistivity while possessing a 50% higher bonding strength. Aging the joints as an exposure to high-temperature circumstances, the arc-sprayed Ni/Bi₂Te₃ joints exhibit much better tolerance to the thermal shock with stable bonding strength and contact resistivity. The enhanced interfacial contact performance and thermal tolerance should be attributed to the thick Ni barrier layer and interface reaction layer with good Ohmic contact. This work provides an effective strategy to establish stable joints for the Bi₂Te₃-based thermoelectric devices with improved thermal stability.

Patterning Design of Electrode to Improve the Interfacial Stability and Rate Capability for Fast Rechargeable Solid-State Lithium-Ion Batteries

Patterned electrodes were developed for use in solid-state lithium-ion batteries, with the ultimate goal to promote fast-charging attributes through improving electrochemically activated surfaces within electrodes. By a conventional photolithography, patterned arrays of SnO₂ nanowires were fabricated directly on the current collector, and empty channel structures formed between the resulting arrays were customized through modifying the size and interval of the SnO₂ patterns. The composite electrolyte comprising Li₇La₃Zr₂O₁₂ and poly(ethylene oxide) was exploited to secure intimate interfacial contact at the electrode/electrolyte junction while preserving ionic conductivity in the bulk electrolyte. The potential and limitation of the electrode patterning approach were then explored experimentally. For example, the electrochemical behaviors of patterned electrodes were investigated as a function of variations in microchannel structures, and compared with those of conventional film-type electrodes. The findings show promise to improve electrode dynamics when electrochemical reaction kinetics could be hindered by poor interfacial characteristics on electrodes.

Hierarchical Ultrathin Layered GO-ZnO@CeO(2) Nanohybrids for Highly Efficient Methylene Blue Dye Degradation

Highly efficient interfacial contact between components in nanohybrids is a key to achieving great photocatalytic activity in photocatalysts and degradation of organic model pollutants under visible light irradiation. Herein, we report the synthesis of nano-assembly of graphene oxide, zinc oxide and cerium oxide (GO-ZnO@CeO₂) nanohybrids constructed by the hydrothermal method and subsequently annealed at 300 °C for 4 h. The unique graphene oxide sheets, which are anchored with semiconducting materials (ZnO and CeO₂ nanoparticles), act with a significant role in realizing sufficient interfacial contact in the new GO-ZnO@CeO₂ nanohybrids. Consequently, the nano-assembled structure of GO-ZnO@CeO₂ exhibits a greater level (96.66%) of MB dye degradation activity than GO-ZnO nanostructures and CeO₂ nanoparticles on their own. This is due to the thin layers of GO-ZnO@CeO₂ nanohybrids with interfacial contact, suitable band-gap matching and high surface area, preferred for the improvement of photocatalytic performance. Furthermore, this work offers a facile building and cost-effective construction strategy to synthesize the GO-ZnO@CeO₂ nanocatalyst for photocatalytic degradation of organic pollutants with long-term stability and higher efficiency.

Bridging the Interfacial Contact for Improved Stability and Efficiency of Inverted Perovskite Solar Cells

Inverted perovskite solar cells (PSCs) have received widespread attention due to their facile fabrication and wide applications. However, their power conversion efficiency (PCE) is reported lower than that of regular PSCs because of the undesirable interfacial contact between perovskite and the hydrophobic hole transport layer (HTL). Here, an interface regulation strategy is proposed to overcome this limitation. A small molecule ([2-(9H-carbazol-9-yl) ethyl] phosphonic acid, abbreviated as 2P), composed of carbazole and phosphonic acid groups, is inserted between perovskite and HTL. Morphological characterization and theoretical calculation reveal that perovskite bonds stronger on 2P-modified HTL than on pristine HTL. The improved interfacial contact facilitates hole extraction and retards degradation. Upon the incorporation of 2P, inverted PSCs deliver a high PCE of over 22% with superior stability, keeping 84.6% of initial efficiency after 7200 h storage under an ambient atmosphere with a relative humidity of ≈30-40%. This strategy provides a simple and efficient way to boost the performance of inverted PSCs.

Amorphous Titanium Polysulfide Composites with Electronic/Ionic Conduction Networks for All-Solid-State Lithium Batteries

All-solid-state lithium/sulfide batteries are considered as next-generation high-energy-density batteries with unrivaled safety. However, sulfide cathodes generally suffer from insulating properties and huge volume expansion in all-solid-state lithium batteries. Based on amorphous TiS₄ (a-TiS₄), a certain proportion of Super P is introduced to suppress the volume expansion and increase the electronic conductivity. Meanwhile, a Li₇P₃S₁₁ solid electrolyte is in situ coated on the surface of 20% Super P/a-TiS₄, and the close interfacial contact between the active material and the solid electrolyte constructs a favorable ionic conduction path. As a result, a Li/75% Li₂S-24% P₂S₅-1% P₂O₅/Li₁₀GeP₂S₁₂/20% Super P/a-TiS₄@Li₇P₃S₁₁ battery shows a high reversible capacity of 507.4 mAh g^-1 after 100 cycles at 0.1 A g^-1. Even the current density increases to 1.0 A g^-1, and it can also provide a reversible capacity of 349.8 mAh g^-1 after 200 cycles. These results demonstrate a promising 20% Super P/a-TiS₄@Li₇P₃S₁₁ cathode material with electronic/ionic conduction networks for all-solid-state lithium batteries.

Ultrastable Interfacial Contacts Enabling Unimpeded Charge Transfer and Ion Diffusion in Flexible Lithium-Ion Batteries

Deteriorating interfacial contact under mechanical deformation induces large cracks and high charge transfer resistance, resulting in a severe capacity fading of flexible lithium-ion batteries (LIBs). Herein, an oxygen plasma treatment on a polymer separator combined with high-speed centrifugal spraying to construct ultrastable interfacial contacts is reported. With the treatment, abundant hydrophilic oxygen-containing functional groups are produced and ensure strong chemical adhesion between the separator and the active materials. With single walled carbon nanotubes (SWCNTs) sprayed onto the active materials, a dense thin film is formed as the current collector. Meanwhile, the centrifugal force caused by high-speed rotation together with van der Waals forces under fast evaporation produces a much closer interface between the current collector and the active materials. As a result of this ultrastable interfacial interaction, the integrated electrode shows no structural failure after 5000 bending cycles with the charge-transfer resistance as low as 35.8% and a Li-ion diffusion coefficient nearly 19 times of the untreated electrode. Flexible LIBs assembled with these integrated electrodes show excellent structural and electrochemical stability, and can work steadily under various deformed states and repeated bending. This work provides a new technique toward rational design of electrode configuration for flexible LIBs.

Immobilizing Ceramic Electrolyte Particles into a Gel Matrix Formed In Situ for Stable Li-Metal Batteries

Hybrid solid/gel electrolytes (SGEs) have generated much research attentions because of their capability to suppress Li dendrite growth and improve battery safety. However, the interfacial compatibility of the electrode/electrolyte or polymer/inorganic ceramics within hybrid electrolytes remains challenging for practical applications. Herein, an SGE is fabricated by confining ceramic particles (Li₇La₃Zr₂O₁₂; LLZO) into in situ formed tetraethylene glycol dimethyl ether (G4)-based gel electrolytes within assembled cells. A hierarchical layered structure is formed when LLZO settles near the Li anode within the liquid electrolyte during the gradual gelatinization process. Good interfacial compatibility is obtained from good contact with the liquid G4 component. The LLZO layer also serves as an ionic sieve to redistribute the Li deposition. This SGE endows stable Li stripping/plating cycling over 800 h at 0.5 mA/cm² (60 °C). Moreover, Li-metal batteries with an SGE coupled with LiFePO₄ and an air cathode both exhibit superior cycling performance. This work presents a promising strategy for hierarchically layered SGEs for high-performance Li-metal batteries.

High Energy Density Single-Crystal NMC/Li6PS5Cl Cathodes for All-Solid-State Lithium-Metal Batteries

To match the high capacity of metallic anodes, all-solid-state batteries require high energy density, long-lasting composite cathodes such as Ni-Mn-Co (NMC)-based lithium oxides mixed with a solid-state electrolyte (SSE). However in practice, cathode capacity typically fades due to NMC cracking and increasing NMC/SSE interface debonding because of NMC pulverization, which is only partially mitigated by the application of a high cell pressure during cycling. Using smart processing protocols, we report a single-crystal particulate LiNi_0.83Mn_0.06Co_0.11O₂ and Li₆PS₅Cl SSE composite cathode with outstanding discharge capacity of 210 mA h g^-1 at 30 °C. A first cycle coulombic efficiency of >85, and >99% thereafter, was achieved despite a 5.5% volume change during cycling. A near-practical discharge capacity at a high areal capacity of 8.7 mA h cm^-2 was obtained using an asymmetric anode/cathode cycling pressure of only 2.5 MPa/0.2 MPa.

19% Efficient P3CT-Na Based MAPbI3 Solar Cells with a Simple Double-Filtering Process

A high-efficiency inverted-type CH₃NH₃PbI₃ (MAPbI₃) solar cell was fabricated by using a ultrathin poly[3-(4-carboxybutyl)thiophene-2,5-diyl]-Na (P3CT-Na) film as the hole transport layer. The averaged power conversion efficiency (PCE) can be largely increased from 11.72 to 18.92% with a double-filtering process of the P3CT-Na solution mainly due to the increase in short-circuit current density (J_SC) from 19.43 to 23.88 mA/cm², which means that the molecular packing structure of P3CT-Na thin film can influence the formation of the MAPbI₃ thin film and the contact quality at the MAPbI₃/P3CT-Na interface. Zeta potentials, atomic-force microscopic images, absorbance spectra, photoluminescence spectra, X-ray diffraction patterns, and Raman scattering spectra are used to understand the improvement in the J_SC. Besides, the light intensity-dependent and wavelength-dependent photovoltaic performance of the MAPbI₃ solar cells shows that the P3CT-Na thin film is not only used as the hole transport layer but also plays an important role during the formation of a high-quality MAPbI₃ thin film. It is noted that the PCE values of the best P3CT-Na based MAPbI₃ solar cell are higher than 30% in the yellow-to-near infrared wavelength range under low light intensities. On the other hand, it is predicted that the double-filtering method can be readily used to increase the PCE of polymer based solar cells.

High-Efficiency Perovskite Light-Emitting Diodes with Improved Interfacial Contact

Unbalanced charge injection is one of the major issues that hampers the efficiency of perovskite light-emitting diodes (PeLEDs). Through engineering the device structure with multiple hole transport layers (HTLs), i.e., poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)diphenylamine) (TFB)/poly(9-vinylcarbazole) (PVK) and nickel oxide (NiO_x)/TFB/PVK, efficient PeLED devices have been successfully demonstrated. However, in a typical solution-processed PeLED with multiple HTLs, the underlying conjugated HTL could be easily redissolved by the ink of the following one, which not only dramatically deteriorates the electrical property of HTLs but also influences the quality of the top perovskite films. In this work, through inserting a thin atomic layer-deposited aluminum oxide (Al₂O₃) layer between HTLs and the perovskite layer, an improved interfacial contact can be achieved, which enables us to obtain perovskite films with enhanced characteristics and balanced charge injection in the resultant PeLEDs. In addition, because of the proper refractive index (r), the presence of the Al₂O₃ layer also favors the light out-coupling of PeLEDs. As a result, we fabricate green PeLEDs with good repeatability and external quantum efficiency of 17.0%, which is approximately 60% higher than that of the control device without Al₂O₃. Our work provides a promising avenue to enhance interfacial contact between the charge transport layer and perovskite for efficient perovskite-based optoelectronic devices.

The Importance of the Interfacial Contact: Is Reduced Graphene Oxide Always an Enhancer in Photo(Electro)Catalytic Water Oxidation?

Optimizing interfacial contact between graphene and a semiconductor has often been proposed as essential for improving their charge interactions. Herein, we fabricated bismuth vanadate-reduced graphene oxide (BiVO₄/rGO) composites with tailored interfacial contact extents and revealed their disparate behavior in photoelectrochemical (PEC) and powder suspension (PS) water oxidation systems. BiVO₄/rGO with a high rGO coverage on the BiVO₄ surface (BiVO₄/rGO HC) exhibited an 8-fold enhancement in the PEC photocurrent density with respect to neat BiVO₄ at 0 V versus Ag/AgCl, while BiVO₄/rGO with a low rGO coverage (BiVO₄/rGO LC) gave a lesser 3-fold enhancement. In contrast, BiVO₄/rGO HC delivered a detrimental effect, while BiVO₄/rGO LC exhibited an enhanced performance for oxygen evolution in the PS system. The phenomenon is attributed to changes in the hydrophobicity of the BiVO₄/rGO composite in conjunction with the interfacial contact configuration. A better BiVO₄/rGO interfacial contact was found to improve the charge separation efficiency and charge transfer ability of the composite material, explaining the superior PEC performance of BiVO₄/rGO HC. Additionally, optimization of the interfacial contact extent was revealed to further improve the energetics of the composite material, as evidenced by a Fermi level shift to a more negative potential. However, the high hydrophobicity of BiVO₄/rGO HC arising from the higher rGO reduction extent triggered poor water miscibility, reducing the surface wettability and therefore hampering the photocatalytic O₂ evolution activity of the sample. The study underlines water miscibility as a governing issue in the PS system.

Nanoscaled Na3PS4 Solid Electrolyte for All-Solid-State FeS2/Na Batteries with Ultrahigh Initial Coulombic Efficiency of 95% and Excellent Cyclic Performances

Nanosized Na₃PS₄ solid electrolyte with an ionic conductivity of 8.44 × 10^-5 S cm^-1 at room temperature is synthesized by a liquid-phase reaction. The resultant all-solid-state FeS₂/Na₃PS₄/Na batteries show an extraordinary high initial Coulombic efficiency of 95% and demonstrate high energy density of 611 Wh kg^-1 at current density of 20 mA g^-1 at room temperature. The outstanding performances of the battery can be ascribed to good interface compatibility and intimate solid-solid contact at FeS₂ electrode/nanosized Na₃PS₄ solid electrolytes interface. Meanwhile, excellent cycling stability is achieved for the battery after cycling at 60 mA g^-1 for 100 cycles, showing a high capacity of 287 mAh g^-1 with the capacity retention of 80%.

Facile Approach to Preparing a Vanadium Oxide Hydrate Layer as a Hole-Transport Layer for High-Performance Polymer Solar Cells

We demonstrate a facile and green approach to preparing a vanadium oxide hydrate (VO_x·nH₂O) layer to serve as the hole-transport layer (HTL) in high-performance polymer solar cells (PSCs). The VO_x·nH₂O layer was in situ prepared by a combined H₂O₂ and ultraviolet-ozone (UVO) processing on a VO_x layer. The as-prepared VO_x·nH₂O layer featured a work function of 5.0 ± 0.1 eV, high transmittance, and better interface properties compared to those of the generally prepared VO_x (UVO or thermal annealing) layers. PSCs based on poly[(ethylhexyl-thiophenyl)-benzodithiophene-(ethylhexyl)-thienothiophene]/[6,6]-phenyl-C₇₁-butyric acid methyl ester using the VO_x·nH₂O layer as the HTL yielded high power conversion efficiencies (PCEs) up to 8.11%, outperforming the devices with VO_x layers (PCE of 6.79% for the UVO-processed VO_x layer and 6.10% for the thermally annealed VO_x layer) and conventional polyethylenedioxythiophene-polystyrenesulfonate (PEDOT:PSS) layers (PCE of 7.67%). The improved PCE was attributed to the enhanced J_SC and/or fill factor, which mainly correlate to the improved interfacial contact between the photoactive layer and the indium tin oxide/HTL or cathode when using the VO_x·nH₂O layer as the HTL. A similar improvement in the PCE was also observed for the PSCs based on poly(3-hexylthiophene)/[6,6]-phenyl-C₆₁-butyric acid methyl ester. In addition, PSCs with a VO_x·nH₂O layer as the HTL showed a higher stability than that of those with a PEDOT:PSS layer. Hence, it would be possible to use this simply and in situ prepared VO_x·nH₂O layer as an inexpensive HTL for high-performance PSCs.

Toward Lower Overpotential through Improved Electron Transport Property: Hierarchically Porous CoN Nanorods Prepared by Nitridation for Lithium-Oxygen Batteries

To lower the overpotential of a lithium-oxygen battery, electron transport at the solid-to-solid interface between the discharge product Li2O2 and the cathode catalyst is of great significance. Here we propose a strategy to enhance electron transport property of the cathode catalyst by the replace of oxygen atoms in the generally used metal oxide-based catalysts with nitrogen atoms to improve electron density at Fermi energy after nitridation. Hierarchically porous CoN nanorods were obtained by thermal treatment of Co3O4 nanorods under ammonia atmosphere at 350 °C. Compared with that of the pristine Co3O4 precursor before nitridation, the overpotential of the obtained CoN cathode was significantly decreased. Moreover, specific capacity and cycling stability of the CoN nanorods were enhanced. It is assumed that the discharged products with different morphologies for Co3O4 and CoN cathodes might be closely associated with the variation in the electronic density induced by occupancy of nitrogen atoms into interstitial sites of metal lattice after nitridation. The nitridation strategy for improved electron density proposed in this work is proved to be a simple but efficient way to improve the electrochemical performance of metal oxide based cathodes for lithium-oxygen batteries.