Superlithiated Polydopamine Derivative for High-Capacity and High-Rate Anode for Lithium-Ion Batteries

High-strength nacre-like composite films based on pre-polymerised polydopamine and polyethyleneimine cross-linked MXene layers via multi-bonding interactions

Demands for high-strength flexible electrodes have significantly increased across various fields, especially in wearable electronics. Inspired by the strong integrated layered structure of the natural nacre via multi-bonding interactions, we report the fabrication of the strong integrated nacre-like composite films based on pre-polymerised polydopamine and polyethyleneimine cross-linked MXene layers (p-DEM), achieving the synergic effect of hydrogen bonding, covalent bonding and electrostatic interactions. As a result, a high-level tensile strength of ∼302 MPa, 10.8 times higher than that of the plain MXene film, is obtained for the prepared p-DE0.5M composite film. Meanwhile, the composite film also delivers superior energy storage (∼1218F cm-3 at 5 mV s-1) and rate performances (capacitance retention of 81.3% at 1000 mV s-1). To demonstrate the practical application of the composite films, a symmetrical supercapacitor based on p-DE0.5M electrodes is assembled, which shows stable energy storage performances under different deformation states such as bending angles at 0, 60, 90 and 180°, or withstand repeated bending times (1000 cycles). This type of multi-bonding interactions induced strong integrated MXene assembly may promote the wide applications of MXene-based films in flexible electronics, artificial intelligence, and tissue engineering, to name a few.

Achieving High Thermal Conductivity and Satisfactory Insulating Properties of Elastomer Composites by Self-Assembling BN@GO Hybrids

With increasing heat accumulation in advanced modern electronic devices, dielectric materials with high thermal conductivity (λ) and excellent electrical insulation have attracted extensive attention in recent years. Inspired by mussel, hexagonal boron nitride (hBN) and graphene oxide (GO) are assembled to construct mhBN@GO hybrids with the assistance of poly(catechol-polyamine). Then, mhBN@GO hybrids are dispersed in carboxy nitrile rubber (XNBR) latex via emulsion coprecipitation to form elastomer composites with a high λ and satisfactory insulating properties. Thanks to the uniform dispersion of mhBN@GO hybrids, the continuous heat conduction pathways exert a significant effect on enhancing the λ and decreasing the interface thermal resistance of XNBR composites. In particular, the λ value of 30 vol% mhBN@GO/XNBR composite reaches 0.4348 W/(m·K), which is 2.7 times that of the neat XNBR (0.1623 W/(m·K)). Meanwhile, the insulating hBN platelets hinder the electron transfer between adjacent GO sheets, leading to satisfactory electrical insulation in XNBR composites, whose AC conductivity is as low as 10^-10 S/cm below 100 Hz. This strategy opens up new prospects in the assembly of ceramic and carbonaceous fillers to prepare dielectric elastomer composites with high λ and satisfactory electrical insulation, making them promising for modern electrical systems.

Porous biscuit-like nanoplate FeNb11O29-x@C for lithium-ion storage and oxygen evolution

The development of efficient and stable electrode materials for lithium-ion batteries (LIBs) and the oxygen evolution reaction (OER) is critical for clean and sustainable energy storage and conversion. In this work, porous biscuit-like nanoplate FeNb₁₁O_29-x@C is reasonably prepared by morphology control and microstructure modification, and presents many advantages in LIBs and the OER. In particular, FeNb₁₁O_29-x@C displays a large specific surface area, abundant active sites and a significant edge effect, thus improving the Li⁺ reactivity and OER kinetics. Meanwhile, the oxygen vacancies and lattice defects in FeNb₁₁O_29-x@C enhance the Li⁺ transport rate and reduce the OER barrier. In addition, the carbon layer structure not only inhibits the irreversible reaction between the electrolyte and metal ions, but promotes the stability, cycling ability and conductivity of LIBs and the OER. Generally, FeNb₁₁O_29-x@C demonstrates good electrochemical performance in LIBs (providing 240.8 mA h g^-1 reversible capacity at a current density of 0.25C and just 0.98% capacity attenuation after 500 cycles at a current density of 10C). Again, it also shows high catalytic performance in the OER (a low overpotential (290 mV@10 mA cm^-2), a small Tafel slope (44.4 mV dec^-1) and desirable catalytic stability).

KOH activated nitrogen and oxygen co-doped tubular carbon clusters as anode material for boosted potassium-ion storage capability

Carbon nanomaterials have become a promising anode material for potassium-ion batteries (KIBs) due to their abundant resources, low cost, and excellent conductivity. However, among carbon materials, the sluggish reaction kinetics and inferior cycle life severely restrict their commercial development as KIBs anodes. It is still a huge challenge to develop carbon materials with various structural advantages and ideal electrochemical properties. Therefore, it is imperative to find a carbon material with heteroatom doping and suitable nanostructure to achieve excellent electrochemical performance. Benefiting from a Na₂SO₄template-assisted method and KOH activation process, the KOH activated nitrogen and oxygen co-doped tubular carbon (KNOCTC) material with a porous structure exhibits an impressive reversible capacity of 343 mAh g^-1at 50 mA g^-1and an improved cyclability of 137 mAh g^-1at 2 A g^-1after 3000 cycles with almost no capacity decay. The kinetic analysis indicates that the storage mechanism in KNOCTC is attributed to the pseudocapacitive process during cycling. Furthermore, the new synthesis route of KNOCTC provides a new opportunity to explore carbon-based potassium storage anode materials with high capacity and cycling performance.

Three-dimensional thiophene-diketopyrrolopyrrole-based molecules/graphene aerogel as high-performance anode material for lithium-ion batteries

Herein, 3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (TDPP) and di-tert-butyl 2,2'-(1,4-dioxo-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-2,5(1H,4H)-diyl)diacetate (TDPPA) were synthesized, which were then loaded in graphene aerogels. The as-prepared thiophene-diketopyrrolopyrrole-based molecules/reduced graphene oxide composites for lithium-ion battery (LIB) anode composites consist of DPPs nanorods on a graphene network. In relation to the DPPs part, embedding DPPs nanorods into graphene aerogels can effectively reduce the dissolution of DPPs in the electrolyte. It can serve to prevent electrode rupture and improve electron transport and lithium-ion diffusion rate, by partially connecting DPPs nanorods through graphene. The composite not only has a high reversible capacity, but also shows excellent cycling stability and performance, due to the densely distributed graphene nanosheets forming a three-dimensional conductive network. The TDPP₆₀ electrode exhibits high reversible capacity and excellent performance, showing an initial discharge capacity of 835 mA h g^-1 at a current density of 100 mA g^-1. Even at a current density of 1000 mA g^-1, after 500 cycles, it still demonstrates a discharge capacity of 303 mA h g^-1 with a capacity retention of 80.7%.

Gifts from Nature: Bio-Inspired Materials for Rechargeable Secondary Batteries

Materials in nature have evolved to the most efficient forms and have adapted to various environmental conditions over tens of thousands of years. Because of their versatile functionalities and environmental friendliness, numerous attempts have been made to use bio-inspired materials for industrial applications, establishing the importance of biomimetics. Biomimetics have become pivotal to the search for technological breakthroughs in the area of rechargeable secondary batteries. Here, the characteristics of bio-inspired materials that are useful for secondary batteries as well as their benefits for application as the main components of batteries (e.g., electrodes, separators, and binders) are discussed. The use of bio-inspired materials for the synthesis of nanomaterials with complex structures, low-cost electrode materials prepared from biomass, and biomolecular organic electrodes for lithium-ion batteries are also introduced. In addition, nature-derived separators and binders are discussed, including their effects on enhancing battery performance and safety. Recent developments toward next-generation secondary batteries including sodium-ion batteries, zinc-ion batteries, and flexible batteries are also mentioned to understand the feasibility of using bio-inspired materials in these new battery systems. Finally, current research trends are covered and future directions are proposed to provide important insights into scientific and practical issues in the development of biomimetics technologies for secondary batteries.

Bismuth Nanoparticles Confined in Carbonaceous Nanospheres as Anodes for High-Performance Potassium-Ion Batteries

Bismuth (Bi) has been considered as a promising alloying-type anode for potassium-ion batteries (PIBs), owing to its high theoretical capacity and suitable working voltage plateaus. However, Bi suffers from dramatic volume fluctuation and significant pulverization during the discharge/charge processes, resulting in fast capacity decay. Herein, we synthesize Bi nanoparticles confined in carbonaceous nanospheres (denoted as Bi@C) for PIBs by first utilizing BiOCl nanoflakes as a hard template and a Bi precursor. The construction of the loose structure buffers the mechanical stresses resulting from the volume expansion of Bi during the alloying reaction and avoids the fracture of the electrode structure, thus improving the cycling performance. Moreover, the carbonaceous layers increase the electronic conductivity and disperse the Bi nanoparticles, enhancing the charge transportation and ionic diffusion, which further promotes the rate capability of Bi@C. It exhibits a superior capacity (389 mAh g^-1 at 100 mA g^-1 after 100 cycles), excellent cycling stability (206 mAh g^-1 at 500 mA g^-1 over 1000 cycles), and an improved rate capability (182 mAh g^-1 at 2.0 A g^-1). This work provides a new structuring strategy in alloying materials for boosting reversible and stable potassium-ion storage.

Preparation Strategies and Applications of MXene-Polymer Composites: A Review

As a new member of the 2D material family, MXene integrates high metallic conductivity and hydrophilic property simultaneously. It shows tremendous potential in fields of energy storage, sensing, electromagnetic shielding, and so forth. Due to the abundant surface functional groups, the physical and chemical properties of MXene can be tuned by the formation of MXene-polymer composites. The introduction of polymers can expand the interlayer spacing, reduce the distance of ion/electron transport, improve the surface hydrophilicity, and thus guide the assembly of MXene-polymer structures. Herein, the preparation strategies of MXene-polymer composites including physical mixing, surface modification, such as anchoring through TiN and Ti-O-C bonds, bonding through esterification, grafting functional groups through TiOSi/TiOP bonds, photograft reaction, as well as in situ polymerization are highlighted. In addition, the possible mechanisms for each strategy are explained. Furthermore, the applications of MXene-polymer composites obtained by different preparation strategies are summarized. Finally, perspectives and challenges are presented for the designs of MXene-polymer composites.

Flake (NH4)6Mo7O24/ Polydopamine as a High Performance Anode for Lithium Ion Batteries

Ammonium molybdate tetrahydrate ((NH₄)₆Mo₇O₂₄) (AMT) is commonly used as the precursor to synthesize Mo-based oxides or sulfides for lithium ion batteries (LIBs). However, the electrochemical lithium storage ability of AMT itself is unclear so far. In the present work, AMT is directly examined as a promising anode material for Li-ion batteries with good capacity and cycling stability. To further improve the electrochemical performance of AMT, AMT/polydopamine (PDA) composite was simply synthesized via recrystallization and freeze drying methods. Unlike with block shape for AMT, the as-prepared AMT/PDA composite shows flake morphology. The initial discharge capacity of AMT/PDA is reached up to 1471 mAh g⁻¹. It delivers a reversible discharge capacity of 702 mAh g⁻¹ at a current density of 300 mA g⁻¹, and a stable reversible capacity of 383.6 mA h g⁻¹ is retained at a current density of 0.5 A g⁻¹ after 400 cycles. Moreover, the lithium storage mechanism is fully investigated. The results of this work could potentially expand the application of AMT and Mo-based anode for LIBs.

Long-term cycling stability of NiCo2S4 hollow nanowires supported on biomass-derived ultrathin N-doped carbon 3D networks as an anode for lithium-ion batteries

A bio-based N-doped carbon 3D network is designed to fabricate a composite anode for LIBs. Benefiting from the highly active substrate and the supported NiCo2S4 hollow nanowires, the composites exhibit an ultrahigh reversible capacity of 1198 mA h g-1 after 500 cycles, holding great potential for long-term applications.

Recent Advanced on the MXene-Organic Hybrids: Design, Synthesis, and Their Applications

With increasing research interest in the field of flexible electronics and wearable devices, intensive efforts have been paid to the development of novel inorganic-organic hybrid materials. As a newly developed two-dimensional (2D) material family, MXenes present many advantages compared with other 2D analogs, especially the variable surface terminal groups, thus the infinite possibility for the regulation of surface physicochemical properties. However, there is still less attention paid to the interfacial compatibility of the MXene-organic hybrids. To this end, this review will briefly summarize the recent progress on MXene-organic hybrids, offers a deeper understanding of the interaction and collaborative mechanism between the MXenes and organic component. After the discussion of the structure and surface characters of MXenes, strategies towards MXene-organic hybrids are introduced based on the interfacial interactions. Based on different application scenarios, the advantages of MXene-organic hybrids in constructing flexible devices are then discussed. The challenges and outlook on MXene-organic hybrids are also presented.

Sandwich-Structured Ordered Mesoporous Polydopamine/MXene Hybrids as High-Performance Anodes for Lithium-Ion Batteries

Organic polymers have attracted significant interest as electrodes for energy storage devices because of their advantages, including molecular flexibility, cost-effectiveness, and environmentally friendly nature. Nevertheless, the real implementation of polymer-based electrodes is restricted by their poor stability, low capacity, and slow electron-transfer/ion diffusion kinetics. In this work, a sandwich-structured composite of ordered mesoporous polydopamine (OMPDA)/Ti₃C₂T_x has been fabricated by in situ polymerization of dopamine on the surface of Ti₃C₂T_x via employing the PS-b-PEO block polymer as a soft template. The OMPDA layers with vertically oriented, accessible nanopores (∼20 nm) provide a continuous pore channel for ion diffusion, while the Ti₃C₂T_x layers guarantee a fast electron-transfer path. The OMPDA/Ti₃C₂T_x composite anode exhibits high reversible capacity, good rate performance, and excellent cyclability for lithium-ion batteries. The in situ transmission electron microscopy analysis reveals that the OMPDA in the composite only shows a small volume expansion and almost preserves the initial morphology during lithiation. Moreover, these in situ experiments also demonstrate the generation of a stable and ultrathin solid electrolyte interphase layer surrounding the active material, which acts as an electrode protective film during cycling. This study demonstrates the method to develop polymer-based electrodes for high-performance rechargeable batteries.

Cross-Conjugated Polycatechol Organic Cathode for Aqueous Zinc-Ion Storage

The rapid development of aqueous zinc-ion batteries poses a challenge for the exploration of cathode materials with high capacity and long cycle life. Organic materials are considered an appropriate choice owing to their structural flexibility and tunable surface chemistry. However, most organic cathode materials still have some shortcomings, such as low electrical conductivity, high cost, and limited cycling durability. Here, a facile synthesis of a novel organic composite cathode composed of cross-conjugated polycatechol (PC) combined with graphene (PC/G) is reported. The PC/G cathode is used for aqueous zinc-ion storage, wherein many hydroxy groups in the PC/G composite cathode can be converted into redox-active carbonyl groups at the initial discharge-charge. This composite cathode can deliver a high specific capacity of 355 mAh g^-1 at 0.1 C and a specific capacity of 171 mAh g^-1 at 10 C. Moreover, the composite cathode can retain 74.4 % of its initial capacity after 3000 discharge-charge cycles at 2 C. This coordination route to zinc ions within the PC/G composite cathode can avoid the destruction of the cathode material during discharge-charge. This organic cathode shows great promise for reversible zinc-ion storage, bringing aqueous zinc-ion batteries a step closer to future practical applications.

Mechanical Enhancement of Bioinspired Polydopamine Nanocoatings

Inspired by the catechol and amine-rich adhesive proteins of mussels, polydopamine (pDA) has become one of the most widely employed methods for functionalizing material surfaces, powered in part by the versatility and simplicity of pDA film deposition that takes place spontaneously on objects immersed in an alkaline aqueous solution of dopamine monomer. Despite the widespread adoption of pDA as a multifunctional coating for surface modification, it exhibits poor mechanical performance. Attempts to modify the physical properties of pDA by incorporation of oxidizing agents, cross-linkers, or carbonization of the films at ultrahigh temperatures have been reported; however, improving mechanical properties with mild post-treatments without sacrificing the functionality and versatility of pDA remains a challenge. Here, we demonstrate thermal annealing at a moderate temperature (130 °C) as a facile route to enhance mechanical robustness of pDA coatings. Chemical spectroscopy, X-ray scattering, molecular force spectroscopy, and bulk mechanical analyses indicate that monomeric and oligomeric species undergo further polymerization during thermal annealing, leading to fundamental changes in molecular and bulk mechanical behavior of pDA. Considerable improvements in scratch resistance were noted in terms of both penetration depth (32% decrease) and residual depth (74% decrease) for the annealed pDA coating, indicating the enhanced ability of the annealed coating to resist mechanical deformations. Thermal annealing resulted in significant enhancement in the intermolecular and cohesive interactions between the chains in the pDA structure, attributed to cross-linking and increased entanglements, preventing desorption and detachment of the chains from the coating. Importantly, improvements in pDA mechanical performance through thermal annealing did not compromise the ability of pDA to support secondary coating reactions as evidenced by electroless deposition of a metal film adlayer on annealed pDA.