Multi-scale microstructural construction in ultralight graphene aerogels enables super elasticity and unprecedented durability for impact protection materials.

Ultralight graphene aerogels have gained extensive recognition in the impact protection field. However, attaining both elasticity and durability at low material density is challenging due to their intrinsic conflicts. Inspired by the mantis ootheca, we present a simultaneous improvement in the elasticity, durability, and density restrictions of ultralight graphene aerogels via constructing a multiscale honeycomb microstructure (MHM) within the graphene skeleton. This approach enables resulting graphene aerogel to achieve a strength per unit volume of 284.6 cm3 mg-1, the ability to recover its shape within 10 ms after an impact at 3.569 m/s, and maintain 97.2 % of its sample height after 20,000 cycles at 90 % strain. The operand analyses and calculation results reveal that the MHM structure facilitates this aerogel's dual-stage stress transfer pathway. Initially, the macroscale honeycomb structure (millimeter-scale) of the graphene aerogels bear and transmit stress to the surrounding regions, followed by the microscale honeycomb structure (micron-scale) deformation to convert stress kinetic energy into elastic potential energy. This two-stage stress transition mechanism of the MHM structure can effectively mitigate excessive local stress and suppress strain localization, thus providing remarkable elasticity and durability. Ultimately, the obtained graphene aerogel demonstrates promising applications as a fall height detection device and impact protective material.

Zwitterionic cellulose nanofibers-based hydrogels with high toughness, ionic conductivity, and healable capability in cryogenic environments.

Extreme environmental conditions often lead to irreversible structural failure and functional degradation in hydrogels, limiting their service life and applicability. Achieving high toughness, self-healing, and ionic conductivity in cryogenic environments is vital to broaden their applications. Herein, we present a novel approach to simultaneously enhance the toughness, self-healing, and ionic conductivity of hydrogels, via inducing non-freezable water within the zwitterionic cellulose-based hydrogel skeleton. This approach enables resulting hydrogel to achieve an exceptional toughness of 10.8 MJ m-3, rapid self-healing capability (98.9 % in 30 min), and high ionic conductivity (2.9 S m-1), even when subjected to -40 °C, superior to the state-of-the-art hydrogels. Mechanism analyses reveal that a significant amount of non-freezable water with robust electrostatic interactions is formed within zwitterionic cellulose nanofibers-modified polyurethane molecular networks, imparting superior freezing tolerance and versatility to the hydrogel. Importantly, this strategy harnesses the non-freezable water molecular state of the zwitterionic cellulose nanofibers network, eliminating the need for additional antifreeze and organic solvents. Furthermore, the dynamic Zn coordination within these supramolecular molecule chains enhances interfacial interactions, thereby promoting rapid subzero self-healing and exceptional mechanical strength. Demonstrating its potential, this hydrogel can be used in smart laminated materials, such as aircraft windshields.

High Performance Single-Crystal Ni-Rich Cathode Modification via Crystalline LLTO Nanocoating for All-Solid-State Lithium Batteries.

Sulfide-based all-solid-state lithium batteries (ASSLBs) assembled with Ni-rich layered cathodes are currently promising candidates for achieving high-energy-density and high-safety energy storage systems. However, the interfacial challenges between sulfide electrolyte and Ni-rich layered cathode, such as space charge layer, side reaction, and poor physical contact, greatly limit the practicality of all-solid-state batteries. In this work, an optimal crystalline Li0.35La0.55TiO3 (LLTO) surface coating with a thickness of roughly 6 nm and a high Li ion conductivity of 0.3 mS cm-1 was adopted to enhance the structural stability of the single-crystal LiNi0.6Co0.2Mn0.2O2 (S-NCM622) cathode in ASSLBs. Furthermore, due to the high ionic conductivity and chemical stability of the LLTO coating layer, the interfacial problems, involving interfacial reaction and a space charge layer, in sulfide-based all-solid-state batteries have been effectively solved. As a result, the assembled ASSLBs with the S-NCM622@LLTO cathode exhibit high initial capacity (179.7 mAh g-1) at 0.05 C and excellent cycling performance with 84.5% capacity retention after 100 cycles at 0.1 C at room temperature. This work proposes an effective strategy to enhance the performance of Ni-rich layered cathodes for next-generation high-energy-density sulfide-based lithium batteries.

Heat- and freeze-tolerant organohydrogel with enhanced ionic conductivity over a wide temperature range for highly mechanoresponsive smart paint.

Binary solvent-based fabrication permits the conductive organohydrogel to function well at low-temperature environments. However, the deep cryogenic and high temperatures are still threatening the performance of conductive organohydrogels in the application of stretchable electronics, biosensors, and intelligent coatings. Here, a radically new method is developed to introduce propylene and carbonate cellulose nanofibrils into freeze tolerance polymer matrix, and fabricate an antifreezing/antiheating organohydrogel integrated a high mechanical strength (1.6 MPa) and high level of ionic conductivity (4.2 S cm-1) over a wide temperature range (-40 to 100 °C). In this designed system, the propylene carbonate with low freezing point and high boiling point was shown to enhance antifreezing (-40 °C) and antiheating (100 °C) performance of organohydrogel. Furthermore, negative charge-rich cellulose nanofibrils (CNFs) were served as an ion transport channel and nanoreinforcements to boost the conductive and mechanical properties of the organohydrogel. In particular, Molecular Dynamics (MD) simulations reveal that propylene carbonate with high dielectric constant is capable of generating ion migration-facilitated effects, enabling the high ionic conductivity of organohydrogel. Tapping into these attributes, potential applications in mechanoresponsive smart coating have been demonstrated utilizing the appealing organohydrogel as a paint, rendering unprecedented protection and monitoring performance.

Ultralight GO-Hybridized CNTs Aerogels with Enhanced Electronic and Mechanical Properties for Piezoresistive Sensors.

Extremely low density carbon nanotubes/graphene hybrid aerogels (CNG) are highly potential active materials for fabricating flexible devices, owing to synergistic effects with one (nanotubes) and two (graphene) dimensional characters in a single structure. However, conquering the long-standing dilemma among low electronic conductivity and inferior mechanical properties for CNG remains a challenging task. Here, an ultralight CNG aerogel (1.52 mg cm-3) with prominent electronic conductivity and mechanical resilience is facilely fabricated through a triple roles design of the sodium dodecyl sulfate (SDS), namely anchoring metal ions, dispersing carbon nanotubes, and inducing self-assembly. It is demonstrated that the Ba2+ can be effectively anchored into the GO interlayers by coupling it with the SDS to reinforce the intersheet interactions, thereby achieving remarkable improvement in mechanical properties (Young's moduli up to 18.3 kPa). Density functional theory calculations reveal that the anchored Ba2+ acting as molecular bridges can availably reduce the tunneling barrier between the GO sheets and facilitate the multidirectional and fast transport of electronics, inducing the high electrical conductivity of CNG (12.55 S cm-1). Taking advantage of these features, potential applications in flexible sensing devices have been demonstrated utilizing the remarkable CNG as an active material, giving extraordinary sensing performance including high sensitivity (48.6 kPa-1), ultralow detection limit (10 Pa), and ultrafast response (18 ms).

Porous Composite Gel Polymer Electrolyte with Interfacial Transport Pathways for Flexible Quasi Solid Lithium-Ion Batteries.

The growing demand for safer energy storage devices leads to wide research on solid-state lithium-ion batteries. However, as an important component in the solid-state battery, the solid-state electrolyte often encounters problems, especially the low conductivity at room temperature, inhibiting the development of solid-state batteries. Here, improved electrochemical performances of lithium-ion batteries are obtained by designing a composite gel polymer electrolyte with a sponge-like structure. The porous composite gel polymer electrolyte (PCGPE) is developed by a facile phase inversion process of poly(vinylidiene fluoride-hexafluoropropylene) (PVdF-HFP) and Li6.4La3Zr1.4Ta0.6O12 (LLZTO). The solid-state nuclear magnetic resonance test proves the continuous porous structure constructs fast Li-ion transport pathways on internal interfaces. As a result, the ionic conductivity of PCGPE is up to 5.45 × 10-4 S cm-1 at room temperature. Moreover, an initial capacity of 142.2 mAh g-1 and 82.6% capacity retention at 1 C after 350 cycles are successfully achieved in flexible LiFPO4//PCGPE//Li batteries.

Heterovalent Cation Substitution to Enhance the Ionic Conductivity of Halide Electrolytes.

Application of halide electrolytes including Li3InCl6 in all-solid-state lithium-metal batteries is still challenging due to the instability with lithium metal and limited ionic conductivity compared with liquid electrolytes and some sulfides. Here, through Zr substitution, a novel Li2.9In0.9Zr0.1Cl6 electrolyte is synthesized through the ball milling and subsequent annealing process. The ionic conductivity of Li2.9In0.9Zr0.1Cl6 (1.54 mS cm-1 at 20 °C) is nearly double that of original Li3InCl6 (0.88 mS cm-1 at 20 °C). Such conductivity enhancement is mainly attributed to the enlarged interplanar spacing and lattice volume, improved concentration of lithium-ion vacancies created by introducing higher-valence Zr4+, and the change of the preferred orientation from the (001) plane to the (131) plane. As a result, the all-solid-state lithium-metal batteries (ASSLMBs) assembled with the Li2.9In0.9Zr0.1Cl6 electrolyte also demonstrate a higher charge/discharge capacity, better cycle stability, and rate performance during cycling without an extra lithium source at the anode side.

Fluorinated Interface Layer with Embedded Zinc Nanoparticles for Stable Lithium-Metal Anodes.

Lithium-metal batteries are promising candidates for the next-generation energy storage devices. However, notorious dendrite growth and an unstable interface between Li and electrolytes severely hamper the practical implantation of Li-metal anodes. Here, a robust solid electrolyte interphase (SEI) layer with flexible organic components on the top and plentiful LiF together with lithiophilic Zn nanoparticles on the bottom is constructed on Li metal based on the spray quenching method. The fluorinated interface layer exhibits remarkable stability to shield Li from the aggressive electrolyte and restrain dendrite growth. Accordingly, the modified Li electrode delivers a stable cycling for over 400 cycles at 3 mA cm-2 in symmetric cells. An improved capacity retention is also achieved in a full cell with a LiFePO4 cathode. This novel design of the artificial SEI layer offers rational guidance for the further development of high-energy-density lithium-metal batteries.

Room temperature readily self-healing polymer via rationally designing molecular chain and crosslinking bond for flexible electrical sensor.

Mechanically tough polymers with excellent room temperature self-healing capacity have aroused strong interest in soft electronics, electronic skins and flexible energy storage devices. However, achieving such polymers remains a challenge due to tardy diffusion dynamics. Herein, a robust and readily self-healing polymer, which is synthesized by one-pot polymerization among 2,4'-tolylene diisocyanate, isophorone diisocyanate, and poly(oxy-1,4-butanediyl), is achieved through reasonably tuning the hardness of the molecular segment and the strength of the dynamic crosslinking bond. The poly(oxy-1,4-butanediyl) that act as a soft segment can effectively avoid the microphase separation, enabling rapid chain mobility of the polymer at the room temperature. Furthermore, the dual H-bonding from 2,4'-tolylene diisocyanate segment acting as a relatively strong crosslinking bond contributes to high mechanical strength, while the weaker single H-bonding from isophorone diisocyanate segment can efficiently dissipate strain energy by bond rupture, endowing the polymer with rapid room temperature self-healing ability. Featuring state-of-the-art of robust stress strength (≈1.3 MPa), high self-healing efficiency (97% within 6 h), and large tensile strain (≈2100%), the resulting polymers are used for the fabrication of stretchable and self-healable electrical sensor, which can be employed to monitor a variety of physiological activities in real time. The described strategy is promising and universal for healable materials, displaying great potential for developing soft electronics.

Potassium Hexafluorophosphate Additive Enables Stable Lithium-Sulfur Batteries.

Uncontrollable dendrite growth and low Coulombic efficiency are the two main obstacles that hinder the application of rechargeable Li metal batteries. Here, an optimized amount of potassium hexafluorophosphate (KPF6, 0.01 M) has been added into the 2 M LiTFSI/ether-based electrolyte to improve the cycling stability of lithium-sulfur (Li-S) batteries. Due to the synergistic effect of self-healing electrostatic shield effect from K+ cations and the LiF-rich solid electrolyte interphases derived from PF6- anions, the KPF6 additive enables a high Li Coulombic efficiency of 98.8% (1 mA cm-2 of 1 mAh cm-2). The symmetrical Li cell can achieve a stable cycling performance for over 200 cycles under a high Li utilization up to 33.3%. Meanwhile, the polysulfide shuttle has been restrained due to the higher concentration of the LiTFSI in the electrolyte. As a result, the assembled Li-S full cell displays excellent capacity retention with only 0.25% decay per cycle in the final electrolyte. Our work offers a smart approach to improve both the anode and cathode performance by the electrolyte modification of rechargeable Li-S batteries.

Robust, Stretchable, and Self-Healable Supramolecular Elastomers Synergistically Cross-Linked by Hydrogen Bonds and Coordination Bonds.

Polymeric elastomers integrated with high mechanical toughness and excellent self-healing ability can find attractive applications in electronic skin, soft robotics, and electrical devices. However, simultaneously enhancing the mechanical and self-healing properties of elastomers is still a great challenge because it is difficult to balance the effects between strong and weak cross-linking bonds. Here, a novel self-healing elastomer is developed via a one-pot polycondensation reaction between bis(3-aminopropyl)-terminated poly(dimethylsiloxane) and 2,4'-tolylene diisocyanate, followed by being coordinated with Al(III) ions by metal-coordination bonds. In this elastomer system, the quadruple hydrogen bonds not only are able to achieve rapid reformation after fracture but also can dissipate strain energy as a weak dynamic bond, endowing the elastomer with excellent self-healing ability and high stretchability, while the treble Al-coordination bonds acting as a strong dynamic bond contribute to the robust molecular networks, leading to the significantly improved robustness and elasticity of the self-healing elastomer. Owing to the accuracy design, the synthesized elastomer exhibits all the desired properties, including high tensile stress (2.6 MPa), exceptional toughness (∼14.7 MJ m-3), high stretchability (∼1700%), and excellent self-healing ability (90%). The robust self-healing elastomer enables the easy fabrication of flexible electronic skin, which will open a new avenue for next-generation electrical devices.

Extremely elastic and conductive N-doped graphene sponge for monitoring human motions.

Due to the extraordinary properties of great elasticity, ultralow density, and good electrical conduction, macroporous graphene bulk materials are the promising candidate as the sensing materials for flexible electronics. Although a large number of progresses have been made, the piezoresistive effect of graphene does not completely meet requirements for various applications yet. Herein, the nitrogen-doped graphene sponge (NGS) material with well-ordered and uniform macroscopic porous structure in long range has been developed by a simple and low-cost strategy by combining hydrothermal and thermal annealing processes. The resulting NGS possesses superior properties of a low density, large elasticity with 80% of the reversible compressibility and outstanding linear elastic region (up to 30%-40%), favorable structural stability, good electrical conductivity (1.4 S m-1), as well as the outstanding sensing performances of a fine sensitivity (1.33 kP-1), low detection limit (2% strain), excellent linear sensing range (nearly 20%), long term stability (3000 cycles), and fast response (72.4 ms). Based on these prominent performances of NGS, a new type of piezoresistive sensor is fabricated, which can successfully detect the human motions from subtle deformations, including the finger bending with the bending degree of approximately 30° and the tiny pulse perturbation of the wrist joint.

Reducing Structural Defects and Oxygen-Containing Functional Groups in GO-Hybridized CNTs Aerogels: Simultaneously Improve the Electrical and Mechanical Properties To Enhance Pressure Sensitivity.

Three-dimensional graphene oxide-carbon nanotube (GO-CNT, abbreviated as GCNT) aerogels can find wide applications in various fields. Especially, low-density GCNT aerogels featuring both high conductivity and superelasticity are essential requirements for the construction of highly sensitive pressure sensor. However, simultaneous improvement on the electrical and mechanical properties of low-density GCNT is still a great challenge owing to their disordered microstructure, severe structural defects and massive oxygen-containing functional groups. Here, a structurally ordered and less defective GCNT aerogel featuring both high conductivity and superelasticity has been fabricated through alkali induced self-assembly of GO liquid crystals (GO LCs) and CNTs. Our methodology relies on the double roles of KOH solution as dispersant for CNTs and an inducer for the self-assembly of GO LCs nanosheets. The less-defective CNTs acting as reinforcement material contributes to the robust structure networks, leading to the significantly improved conductivity (2.4 S m-1) and elasticity (14.3 kPa) of GCNT. Benefiting from these outstanding properties of GCNT aerogels, the assembled pressure sensor exhibits an ultrahigh sensitivity of 1.22 kPa-1, rapid response time of 28 ms and excellent cycling stability, which enables it as a high-performance sensing platform to monitor various human motions in real time.

Hydroxyalkylation of phenol to bisphenol F over heteropolyacid catalysts: The effect of catalyst acid strength on isomer distribution and kinetics.

Hydroxyalkylation of phenol with formaldehyde to bisphenol F over heteropolyacid impregnated on clay was investigated. These catalysts displayed excellent catalytic performance for this reaction, especially that the effects of acid sites on the isomer distribution are obvious. Various solid catalysts were prepared by impregnating heteropolyacid on different kind of clay matrices, and their chemical compositions, textural properties, and acid strength of the heteropolyacid catalysts were characterized by EDX, BET, NH3-TPD, XRD, and FT-IR. Moreover, the effects of acid sites and reaction temperature on the yield and 4,4'-isomer distribution were launched by comparing the data obtained from the two kinds of catalysts. Furthermore, the kinetics of the hydroxyalkylation of phenol to BPF was established.