Pre-oxidized and composite strategy greatly boosts performance of polyacrylonitrile/LLZO nanofibers for lithium-metal batteries.

The active cyano-group in polyacrylonitrile has severe passivation of lithium anode under larger current density, which restricts the wide application of polyacrylonitrile(PAN) in lithium metal batteries. Herein, in order to address the excessive passivation of lithium metal by PAN, inspired by the pre-oxidation of carbon fibers, PAN was pre-oxidized at 230 °C, which transformed part of the cyano group into a more chemically stable cyclized structure. The electrochemical and mechanical properties of the composite solid electrolyte were effectively improved by introducing the fast ionic conductor Li6.25La3Zr2Al0.25O12 into PAN by electrospinning. The oxidized PAN-based composite solid electrolyte presents high ionic conductivity (3.05 × 10-3 S·cm-1) and high lithium transference number of 0.79 at 25 °C, further contributing to a high electrochemical window (5.3 V). The solid-state batteries assembled by Li||10 wt%-LLZAO@230-oxy-PAN||NCM523 behave superb electrochemical performance, delivering a high initial discharge capacity of 157 mAh g-1 at 0.2 C. After 100 cycles, the capacity retention was 93.3 %, indicating the electrolyte displays great electrochemical stability. This work provides new insights into the structural design of polymer-based high-voltage batteries.

Boosting Thermoelectric Performance via Weakening Carrier-Phonon Coupling in BiCuSeO-Graphene Composites.

BiCuSeO is a promising oxygen-containing thermoelectric material due to its intrinsically low lattice thermal conductivity and excellent service stability. However, the low electrical conductivity limits its thermoelectric performance. Aliovalent element doping can significantly improve their carrier concentration, but it may also impact carrier mobility and thermal transport properties. Considering the influence of graphene on carrier-phonon decoupling, Bi0.88 Pb0.06 Ca0.06 CuSeO (BPCCSO)-graphene composites are designed. For further practical application, a rapid preparation method is employed, taking less than 1 h, which combines self-propagating high-temperature synthesis with spark plasma sintering. The incorporation of graphene simultaneously optimizes the electrical properties and thermal conductivity, yielding a high ratio of weighted mobility to lattice thermal conductivity (144 at 300 K and 95 at 923 K). Ultimately, BPCCSO-graphene composites achieve exceptional thermoelectric performance with a ZT value of 1.6 at 923 K, bringing a ≈40% improvement over BPCCSO without graphene. This work further promotes the practical application of BiCuSeO-based materials and this facile and effective strategy can also be extended to other thermoelectric systems.

An initiator-free and solvent-free in-situ self-catalyzed crosslinked polymer electrolyte for all-solid-state lithium-metal batteries.

Linear polymer (e.g. polyethylene oxide, PEO) based electrolytes have been widely studied due to their flexibility and relatively good contact against electrodes. However, the linear polymers are prone to crystallization at room temperature and melting at moderate temperature, restricting their application in lithium metal batteries. To address these problems, a self-catalyzed crosslinked polymer electrolyte (CPE) was designed and prepared by the reaction of poly (ethylene glycol diglycidyl ether) (PEGDGE) and polyoxypropylenediamine (PPO) with only the bistrifluoromethanesulfonimide lithium salt (LiTFSI) added and with no any initiators. LiTFSI catalyzed the reaction by reducing the activation energy to form a crosslinked network structure, which was identified by calculation, NMR and FTIR. The as-prepared CPE has high resilience and a low glass transition temperature (Tg = -60 °C). Meanwhile, the solvent-free in-situ polymerization technique has been adopted in the assembly of the CPE with electrodes to decrease the interfacial impedance greatly and improve the ionic conductivity to 2.05 × 10-5 S cm-1 and 2.55 × 10-4 S cm-1 at room temperature and 75 °C, respectively. As a result, the in-situ LiFeO4/CPE/Li battery exhibits outstanding thermal and electrochemical stability at 75 °C. Our work has proposed an initiator-free and solvent-free in-situ self-catalyzed strategy of preparing high performance crosslinked solid polymer electrolytes.

A high performance composite separator with robust environmental stability for dendrite-free lithium metal batteries.

The garnet ceramic Li6.4La3Zr1.4Ta0.6O12 (LLZTO) modified separators have been proposed to overcome the poor thermal stability and wettability of commercial polyolefin separators. However, the side reaction of LLZTO in the air leads to deterioration of environmental stability of composite separators (PP-LLZTO), which will limit the electrochemical performance of batteries. Herein, the LLZTO with the polydopamine (PDA) coating (LLZTO@PDA) was prepared by solution oxidation, and then applied it to a commercial polyolefin separator to achieve a composite separator (PP-LLZTO@PDA). LLZTO@PDA is stable in the air, and no Li2CO3 can be observed on the surface even after 90 days in the air. Besides, LLZTO@PDA coating endows the PP-LLZTO@PDA separator with the tensile strength (up to 103 MPa), good wettability (contact angle 0°) and high ionic conductivity (0.93 mS cm-1). Consequently, the Li/PP-LLZTO@PDA/Li symmetric cell cycles stably for 600 h without significant dendrites generation, and the assembled Li//LFP cells with PP-LLZTO@PDA-D30 separators deliver a high capacity retention of 91.8% after 200 cycles at 0.1C. This research provides a practical strategy for constructing composite separators with excellent environmental stability and high electrochemical properties.

Compositing effects for high thermoelectric performance of Cu2Se-based materials.

Thermoelectric materials can realize direct conversion between heat and electricity, showing excellent potential for waste heat recovery. Cu2Se is a typical superionic conductor thermoelectric material having extraordinary ZT values, but its superionic feature causes poor service stability and low mobility. Here, we reported a fast preparation method of self-propagating high-temperature synthesis to realize in situ compositing of BiCuSeO and Cu2Se to optimize the service stability. Additionally, using the interface design by introducing graphene in these composites, the carrier mobility could be obviously enhanced, and the strong phonon scatterings could lead to lower lattice thermal conductivity. Ultimately, the Cu2Se-BiCuSeO-graphene composites presented excellent thermoelectric properties with a ZTmax value of ~2.82 at 1000 K and a ZTave value of ~1.73 from 473 K to 1000 K. This work provides a facile and effective strategy to largely improve the performance of Cu2Se-based thermoelectric materials, which could be further adopted in other thermoelectric systems.

Robust, Flexible Thermoelectric Film for Energy Harvesting by a Simple and Eco-Friendly Method.

As for the self-supporting composite films, it is significant to develop a structural design that allows for excellent flexibility while reducing the negative effect on thermoelectric (TE) properties. Herein, a robust, flexible TE film was fabricated by in situ chemical transformation and vacuum-assisted filtration without any organic solvents involved. The performance of the films was further optimized by adjusting the Ag/Te ratio and post-treatment methods. Owing to the semi-interpenetrating nanonetwork structure formed by AgxTe nanowires and bacterial cellulose, the obtained TE film displayed a high tensile strength of ∼78.4 MPa and a high power factor of 48.9 µW m-1 K-2 at room temperature. A slight electrical conductivity decrement of the TE film in flexible test (∼2% after 1000 bending cycles) indicates an excellent flexibility. Finally, a TE bracelet was assembled to harvest body heat energy, and a steady current of ∼2.7 µA was generated when worn on the wrist indoors. This work provides a reference for the structural design and practical application of flexible TE films.

Application and Research Progress of Covalent Organic Frameworks for Solid-State Electrolytes in Lithium Metal Batteries.

Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers with periodic networks that are constructed from small molecular units via covalent bonds, which have low densities, high porosity, large specific surface area, and ease of functionalization. The one-dimension nanochannels in COFs offer an effective means of transporting lithium ions while maintaining a stable structure over a wide range of temperatures. As a new category of ionic conductors, COFs exhibit unparalleled application potential in solid-state electrolytes. Here, we provide a comprehensive summary of recent applications and research progress for COFs in solid-state electrolytes of lithium metal batteries and discuss the possible development directions in the future. This review is expected to provide theoretical guidance for the design of high-performance solid-state electrolytes.

Novel In Situ Growth of ZIF-8 in Porous Epoxy Matrix for Mechanically Robust Composite Electrolyte of High-Performance, Long-Life Lithium Metal Batteries.

Polymer electrolytes (PEs) with high flexibility, low cost, and excellent interface compatibility have been considered as an ideal substitute for traditional liquid electrolytes for high safety lithium metal batteries (LMBs). Nevertheless, the mechanical strength of PEs is generally poor to prevent the growth of lithium dendrites during the charge/discharge process, which seriously restricts their wide practical applications. Herein, a mechanical robust ZIF-8/epoxy composite electrolyte with unique pore structure was prepared, which effectively inhibited the growth of lithium dendrites. Meanwhile, the in situ growth of ZIF-8 in porous epoxy matrix can promote the uniform flux and fast transport of lithium ions. Ultimately, the optimal electrolyte shows high ionic conductivity (2.2 × 10-3 S cm-1), wide electrochemical window (5 V), and a large Li+ transference number (0.70) at room temperature. The Li||NCM811 cell using the optimal electrolyte exhibits high capacity and excellent cycling performance (83.2% capacity retention with 172.1 mA h g-1 capacity retained after 200 cycles at 0.2 C). These results indicate that the ZIF-8/epoxy composite electrolyte is of great promise for the application in LMBs.

In Situ Constructing Ultrathin, Robust-Flexible Polymeric Electrolytes with Rapid Interfacial Ion Transport in Lithium Metal Batteries.

Safety of lithium metal batteries (LMBs) has been improved by using the solid-state polymer electrolytes, but the performance of LMBs is still troubled by the poor interface of solid electrolytes/electrodes, leading to insufficient interfacial Li+ transport. Here, a novel ultrathin, robust-flexible polymeric electrolyte is achieved by in situ polymerization of 1,3-dioxolane in soft nanofibrous skeleton at room temperature without any extra initiator or plasticizer, leading to the electrolyte with rapid interfacial ion transport. This facilitated Li+ transportation is demonstrated by molecular dynamics simulation. Consequently, the as-prepared electrolyte exhibits excellent cycling performance. The results indicate that the electrolyte works well in the LiFePO4 //Li cell at elevated temperature up to 90 °C, and further matches with the high-voltage LiNi0.8 Mn0.1 Co0.1 O2 cathode. This study provides an effective approach to constructing a practical polymeric electrolyte for fabrication of safe, high performance LMBs.

Dynamical Ion Association and Transport Properties in PEO-LiTFSI Electrolytes: Effect of Salt Concentration.

The association of ions describes the formation of ion species in electrolyte solutions and is strongly related to the salt concentration. However, the discussion of ion species and their transport is ambiguous in some studies on electrolyte materials due to the assumption of ideal solutions. Accordingly, in this work, molecular dynamics simulations are used to study ion association and transport properties of poly(ethylene)oxide (PEO)-lithium bis(trifluoromethanesulfonyl)imide electrolytes over a range of salt concentrations (r = [Li]/[EO]) from 0.01 to 0.20. Based on the analysis of the solvation environment and ion species, it is revealed that the distinct ion-ion correlations exist in two different characteristic areas, with a salt concentration of 0.10 as the limit. Below the critical concentration, the dynamic equilibrium between free ions and ion pairs is the most important process affecting the transport properties of electrolytes, but the process may have a minor influence on the applicability of the Nernst-Einstein relation. In concentrated solutions, a large number of ion pairs, triplets, and so forth appear in the electrolytes. The high-order ion clusters, with an average size of 3.95 at r = 0.20, are the main stable structures for transporting Li+, but the trapped free ions are the most abundant ion species. Meanwhile, the effect of salt concentrations on the average transport of ion clusters is to increase their average lifetime, but their transport rates remain unchanged. In addition, the coupling dynamics between ions and polymers is also discussed in order to gain a complete insight into the importance of salt concentrations.

Ultrahigh Power Factor of Ternary Composites with Abundant Se Nanowires for Thermoelectric Application.

In this work, ultrahigh-performance single-walled carbon nanotube (SWCNT)/Se nanowire (NW)/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) ternary thermoelectric (TE) nanocomposite films are successfully designed by rational design of CNT/Se/PEDOT:PSS ternary nanocomposites. The addition of CNTs apparently improves the electrical conductivity of composite films, resulting in a relatively huge growth of the power factor. The PEDOT:PSS interface layers uniformly attach on both sides of the Se NWs and CNTs effectively, forming a tightly interleaving and interconnected three-dimensional network. As a consequence, a maximum power factor of 863.83 µW/(m·K2) has been achieved for the sample containing 26 wt % CNTs at 434 K. Ultimately, a flexible TE generator prototype consisting of 5-unit freestanding composite film strips is fabricated using the optimized composite films, which can generate a maximum output power of 206.8 nW at a temperature gradient of 44.7 K. Therefore, the present work has a further potential to be used for the flexible polymer/carbon TE nanocomposite films and devices.

Self-Enhancing Gel Polymer Electrolyte by In Situ Construction for Enabling Safe Lithium Metal Battery.

Lithium metal battery (LMB) possessing a high theoretical capacity is a promising candidate of advanced energy storage devices. However, its safety and stability are challenged by lithium dendrites and the leakage of liquid electrolyte. Here, a self-enhancing gel polymer electrolyte (GPE) is created by in situ polymerizing 1,3-dioxolane (DOL) in the nanofibrous skeleton for enabling safe LMB. The nanofiber membrane possesses a better affinity with poly-DOL (PDOL) than commercial separator for constructing homogeneous GPE with enhanced ion conductivity. Furthermore, polydopamine is introduced on nanofiber membrane to form hydrogen bonding with PDOL and bis((trifluoromethyl)sulfonyl)imide anion, dramatically improving the mechanical strength, ionic conductivity, and transference number of GPE. Besides, molecular dynamic simulation is used to reveal the intrinsic factors of high ionic conductivity and reinforcing effect in the meantime. Consequently, the LiFePO4 //Li batteries using self-enhancing GPE show extraordinary cyclic stability over 800 cycles under high current density of 2 C, with a capacity decay of 0.021% per cycle, effectively suppressing the growth of lithium dendrites. This ingenious strategy is expected to manufacture advanced performance and high safety LMBs and compatible with the current battery production.

Flexible Thermoelectric Films Based on Bi2Te3 Nanosheets and Carbon Nanotube Network with High n-Type Performance.

Flexible thermoelectric materials and devices have gained wide attention due to their capability to stably and directly convert body heat or industrial waste heat into electric energy. Many research and synthetic methods of flexible high-performance p-type thermoelectric materials have made great progress. However, their counterpart flexible n-type organic thermoelectric materials are seldom studied due to the complex synthesis of conductive polymer and poor stability of n-type materials. In this work, bismuth tellurium (Bi2Te3) nanosheets are in situ grown on single-walled carbon nanotubes (SWCNTs) assisted by poly(vinylpyrrolidone) (PVP). A series of flexible SWCNTs@Bi2Te3 composite films on poly(vinylidene fluoride) (PVDF) membranes are obtained by vacuum-assisted filtration. The high electrical conductivity of 253.9 S/cm, and a corresponding power factor (PF) of 57.8 µW/m·K2 is obtained at 386 K for SWCNTs@Bi2Te3-0.8 film. Moreover, high electrical conductivity retention of 90% can be maintained after a 300-cycle bending test and no obvious attenuation can be detected after being stored in an Ar atmosphere for 9 months, which exhibits good flexibility and excellent stability of the SWCNTs@Bi2Te3 composite films. This work shows a convenient method to fabricate n-type and flexible thermoelectric composite film and further promotes the practical application of n-type flexible thermoelectric materials.

All-in-One MoS2 Nanosheets Tailored by Porous Nitrogen-Doped Graphene for Fast and Highly Reversible Sodium Storage.

Though being a promising anode material for sodium-ion batteries (SIBs), MoS2 with high theoretical capacity shows poor rate capability and rapid capacity decay, especially involving the conversion of MoS2 to Mo metal and Na2S. Here, we report all-in-one MoS2 nanosheets tailored by porous nitrogen-doped graphene (N-RGO) for the first time to achieve superior structural stability and high cycling reversibility of MoS2 in SIBs. The all-in-one MoS2 nanosheets possess desirable structural characteristics by admirably rolling up all good qualities into one, including vertical alignment, an ultrathin layer, vacancy defects, and expanded layer spacing. Thus, the all-in-one MoS2@N-RGO composite anode exhibits an improvement in the charge transport kinetics and availability of active materials in SIBs, resulting in outstanding cycling and rate performance. More importantly, the restricted growth of all-in-one MoS2 by the porous N-RGO via a strong coupling effect dramatically improves the cycling reversibility of conversion reaction. Consequently, the all-in-one MoS2@N-RGO composite anode demonstrates excellent reversible capacity, outstanding rate capability, and superior cycling stability. This study strongly suggests that the all-in-one MoS2@N-RGO has great potential for practical application in high-performance SIBs.

A highly stretchable dielectric elastomer based on core-shell structured soft polymer-coated liquid-metal nanofillers.

Elastomer, poly(n-butyl methacrylate), coated liquid metal (LM) nanodroplets (EGaIn@PBMA) were successfully fabricated via a facile in situ free radical polymerization method. The as-prepared soft nanoparticles can be directly hot-pressed into nanocomposites which not only exhibited ultra-high stretching flexibility (>400%) but also excellent dielectric properties with remarkably suppressed dielectric loss, showing great promise in the flexible energy-storage field.

High Thermoelectric Performance of AgSb1-xPbxSe2 Prepared by Fast Nonequilibrium Synthesis.

AgSbSe2 is a typical member of cubic I-V-VI2 semiconductors, which are known for their extremely low lattice thermal conductivity (κl). However, the low electrical conductivity of AgSbSe2, below ∼10 S cm-1 at room temperature, has hindered its thermoelectric performance. In this work, single-phase AgSbSe2 bulk samples with much higher electrical conductivity were synthesized via self-propagating high-temperature synthesis (SHS) combined with spark plasma sintering (SPS) for the first time. Pb doping through the nonequilibrium process further increases the electrical conductivity to >100 S cm-1. Furthermore, continuously increased effective mass md* can be achieved upon Pb doping because of the multiple degenerate valence bands of AgSbSe2 and the energy-filtering effect induced by in situ-formed nanodots. The simultaneous enhancement of both the electrical conductivity and Seebeck coefficient contributes to an unprecedentedly high average power factor of 6.75 µW cm-1 K-2. Meanwhile, the introduced dense grain boundaries and point defects enhance the phonon scattering and consequently suppress κl, yielding a high ZT value of 1.2 at 723 K in AgSb0.94Pb0.06Se2. This study opens a new avenue for rapid, low-cost, large-scale production of AgSbSe2-based materials and demonstrates that Pb-doped AgSbSe2 prepared via the SHS-SPS method is a promising candidate for thermoelectric applications.

Effect of resin composition on performance of polymer-infiltrated feldspar-network composites for dental restoration.

This study intends to obtain a kind of polymer-infiltrated ceramic-network (PICN) composite with improved performance for dental restoration. Porous ceramic network was prepared via compressing feldspar powders, followed by resin infiltration using Bis-GMA/TEGDMA or UDMA/TEGDMA mixtures to obtain PICN composites after thermocuring. The sintering parameters (temperature, duration) for the formation of feldspathic network with proper porosity were investigated. The ratios of resin mixtures were adjusted to optimize the infiltration. Comprehensive characterizations were conducted on the porosity and the shrinkage of preformed ceramic-networks, the viscosity of resin mixtures and their infiltration into the ceramic networks, as well as, flexural properties, Vickers hardness and wear resistance of the final PICN composites. It turned out that the PICN composite prepared from Bis-GMA/TEGDMA (6:4) achieved the best performance among all the samples, which is expected to be a suitable material for computer-aided design/computer-aided manufacturing (CAD/CAM) dental restorative applications.

Superresilient Hard Carbon Nanofabrics for Sodium-Ion Batteries.

Developing supermechanically resilient hard carbon materials that can quickly accommodate sodium ions is highly demanded in fabricating durable anodes for wearable sodium-ion batteries. Here, an interconnected spiral nanofibrous hard carbon fabric with both remarkable resiliency (e.g., recovery rate as high as 1200 mm s-1 ) and high Young's modulus is reported. The hard carbon nanofabrics are prepared by spinning and then carbonizing the reaction product of polyacrylonitrile and polar molecules (melamine). The resulting unique hard carbon possesses a highly disordered carbonaceous structure with enlarged interlayer spacing contributed from the strong electrostatic repulsion of dense pyrrolic nitrogen atoms. Its excellent resiliency remains after intercalation/deintercalation of sodium ions. The outstanding sodium-storage performance of the derived anode includes excellent gravimetric capacity, high-power capability, and long-term cyclic stability. More significantly, with a high loading mass, the hard carbon anode displays a high-power capacity (1.05 mAh cm-2 at 2 A g-1 ) and excellent cyclic stability. This study provides a unique strategy for the design and fabrication of new hard carbon materials for advanced wearable energy storage systems.

An Ultra-microporous Carbon Material Boosting Integrated Capacitance for Cellulose-Based Supercapacitors.

A breakthrough in advancing power density and stability of carbon-based supercapacitors is trapped by inefficient pore structures of electrode materials. Herein, an ultra-microporous carbon with ultrahigh integrated capacitance fabricated via one-step carbonization/activation of dense bacterial cellulose (BC) precursor followed by nitrogen/sulfur dual doping is reported. The microporous carbon possesses highly concentrated micropores (~ 2 nm) and a considerable amount of sub-micropores (< 1 nm). The unique porous structure provides high specific surface area (1554 m2 g-1) and packing density (1.18 g cm-3). The synergistic effects from the particular porous structure and optimal doping effectively enhance ion storage and ion/electron transport. As a result, the remarkable specific capacitances, including ultrahigh gravimetric and volumetric capacitances (430 F g-1 and 507 F cm-3 at 0.5 A g-1), and excellent cycling and rate stability even at a high current density of 10 A g-1 (327 F g-1 and 385 F cm-3) are realized. Via compositing the porous carbon and BC skeleton, a robust all-solid-state cellulose-based supercapacitor presents super high areal energy density (~ 0.77 mWh cm-2), volumetric energy density (~ 17.8 W L-1), and excellent cyclic stability.

Enhancing overall properties of epoxy-based composites using polydopamine-coated edge-carboxylated graphene prepared via one-step high-pressure ball milling.

Graphene (GN) nanofillers have been widely used to enhance the overall performance of polymer composites due to their various superior properties, which strongly rely on the uniform dispersion and strong interfacial bonding of GN with high-quality polymer matrices. In the present study, the strengthening and functional effects of polydopamine-coated edge-carboxylated graphene (p-ECG) on the mechanical, moisture-barrier and electromagnetic properties of epoxy (EP)-based composites were systematically evaluated. p-ECG was successfully prepared via one-step high-pressure ball milling through the edge-selective functionalization and exfoliation of pristine graphite in the presence of dry ice, followed by synchronous reduction and coating via the mild oxidative polymerization of mussel-inspired dopamine. p-ECG showed prominent advantages of a small sheet size, excellent dispersibility and high chemical reactivity in the EP matrix. Obvious enhancements were achieved in the tensile and flexural properties and moisture-barrier performance of EP composites as well as the interlaminar shear strength (ILSS) and transverse fiber bundle tensile (TFBT) strength of carbon fiber (CF)/EP composites, which confirmed the excellent dispersion and chemically strengthened interfacial bonding of p-ECG in the EP matrix. More importantly, p-ECG introduced onto the surface of desized CF led to significant enhancement in the electromagnetic interference (EMI) shielding capability of CF/EP composites, which was primarily ascribed to the polarization relaxation effect induced by the defects and functional groups in p-ECG as well as the increase in electrical conductivity derived from the "bridging effect" of p-ECG. Specifically, with p-ECG content of 0.5 wt%, the increments in tensile strength, TFBT strength, shielding effectiveness (total, SET) and shielding effectiveness (reflection loss, SER) were as high as 33.3, 34.3, 31.3 and 71.0%, respectively.