Nitrogen and sulfur co-doped vanadium carbide MXene for highly reversible lithium-ion storage

In Situ TEM Studies of Tunnel-Structured Materials for Alkali Metal-Ion Batteries

Tunnel-structured materials have garnered significant attention as promising candidates for high-performance rechargeable batteries, owing to their unique structural characteristics that facilitate efficient ionic transport. However, understanding the dynamic processes of ionic transport within these tunnels is crucial for their further development and performance optimization. Analytical in situ transmission electron microscopy (TEM) has demonstrated its effectiveness as a powerful tool for visualizing the complex ionic transport processes in real time. In this review, we summarize the state-of-the-art in situ tracking of ionic transport processes in tunnel-structured materials for alkali metal-ion batteries (AMIBs) by TEM observation at the atomic scale, elucidating the fundamental issues pertaining to phase transformations, structural evolution, interfacial reactions and degradation mechanisms. This review covers a wide range of electrode and electrolyte materials used in AMIBs, highlighting the versatility and general applicability of in situ TEM as a powerful tool for elucidating the fundamental mechanisms underlying the performance of AMIBs. Furthermore, this work critically discusses current challenges and future research directions, offering perspectives on the development of next-generation battery materials through advanced in situ characterization techniques.

General and Fast Gas-Solid Synthesis of Functional MXenes and Derivatives on the Scale of Tens of Grams

The rising of MXenes not only enriches the two-dimensional material family but also brings more opportunities for diverse functional applications. However, the controllable synthesis of MXenes is still unsatisfied via the common liquid-solid etching route, considering the unsolved problems like safety risk, time cost and easy oxidation. Herein, a facile yet efficient gas-solid (G-S) reaction methodology is devised by using hydrogen fluoride gas derived from fluorinated organics as the MAX etchant toward high-efficiency fabrication of multiple MXenes and their derivatives. The innovative G-S reaction strategy exhibits superb versatility to achieve different gram-level MXenes (V2C, Ti3C2, Nb2C, Ti2N, Ti3CN, (Mo2/3Y1/3)2C) in a very short time, and even realizes in situ heteroatom doping or synchronous phase conversion of MXenes directly from MAX phases. The obtained MXenes and their derivatives exhibit excellent structure stability and high electron/ion conductivity, making them promising materials for electrochemical applications. In particular, the N-doped V2C MXene shows superior adsorption and catalytic activity toward lithium polysulfides for advanced lithium sulfur batteries.

Prussian Blue Analogues "Dressed" in MXene Nanosheets Tightly for High Performance Lithium-Ion Batteries

MXenes, have been considered as a new generation anode material in lithium-ion batteries for lower lithium-ion diffusion barriers and superior conductivity. Unfortunately, their structures are prone to aggregation and stacking, hindering further shuttle of lithium ions and electrons, resulting in lower discharge capacity. Therefore, the introduction of interlayer spacers for the preparation of MXene-based hybrids has attracted much attention. Introducing Prubssian blue analogues (PBAs) as a new interlayer spacer to combine with MXene nanosheets can not only preserve the high conductivity of MXene and inhibit the volume expansion and structural degradation of the PBA component, but also inherit the characteristics of large specific surface area and high porosity of PBAs. By intelligent regulating the size of MXene sheets, Co-PBA@MXene hybrids with common sandwich-like structures and superior core-shell-like structures have been successfully obtained. Furthermore, Co@M(x:y) hybrids are prepared by intelligently adjusting the shell thickness of MXene through intelligently controlling of the mass ratio between Co-PBA and MXene. Among them, the Co@M(5:2) anode exhibits an excellent capacity (603 mA h g-1 at 0.2 A g-1 after 100 cycles) and superior long-term cycling stability due to the protective and conductive properties provided by the MXene shell and multi-redox pairs and rich porosity from Co-PBA core.

V-MXenes for Energy Storage/Conversion Applications

MXenes, a two-dimensional (2D) material, exhibit excellent optical, electrical, chemical, mechanical, and electrochemical properties. Titanium-based MXene (Ti-MXene) has been extensively studied and serves as the foundation for 2D MXenes. However, other transition metals possess the potential to offer excellent properties in various applications. This comprehensive review aims to provide an overview of the properties, challenges, key findings, and applications of less-explored vanadium-based MXenes (V-MXenes) and their composites. The current trends in V-MXene and their composites for energy storage and conversion applications have been thoroughly summarized. Overall, this review offers valuable insights, identifies potential opportunities, and provides key suggestions for future advancements in the MXenes and energy storage/conversion applications.

Hydrogen-Bonded Organic Framework Derived 2D N, O Co-Doped Carbon Nanobelt with Tunable Pseudocapacitive Contribution for Efficient Capacitive Deionization

Defect engineering is recognized as an attractive method for modulating the electronic structure and physicochemical characteristics of carbon materials. Exploiting heteroatom-doped porous carbon with copious active sites has attracted great attention for capacitive deionization (CDI). However, traditional methods often rely on the utilization of additional heteroatom sources and strong corrosive activators, suffering from low doping efficiency, insufficient doping level, and potential biotoxicity. Herein, hydrogen-bonded organic frameworks (HOFs) are employed as precursors to synthesize N, O co-doped porous carbon via a simple and green reverse defect engineering strategy, achieving controllable heavy doping of heteroatoms. The N, O co-doping triggers significant pseudocapacitive contribution and the surface pore structure supports the formation of the electric double layer. Therefore, when HOF-derived N, O co-doped carbon is used as CDI electrodes, a superior salt adsorption capacity of 32.29 ± 1.42 mg g-1 and an outstanding maximum salt adsorption rate of 10.58 ± 0.46 mg g-1 min-1 at 1.6 V in 500 mg L-1 NaCl solution are achieved, which are comparable to those of state-of-the-art carbonaceous electrodes. This work exemplifies the effectiveness of the reverse nitrogen-heavy doping strategy on improving the carbon structure, shedding light on the further development of rational designed electrode materials for CDI.

In-situ synthesized and induced vertical growth of cobalt vanadium layered double hydroxide on few-layered V2CTx MXene for high energy density supercapacitors

Two-dimensional (2D) MXene nanomaterials display great potential for green energy storage. However, as a result of self-stacking of MXene nanosheets and the presence of conventional binders, MXene-based nanomaterials are significantly hindered in their rate capability and cycling stability. We successfully constructed a self-supported stereo-structured composite (TMA-V2CTx/CoV-LDH/NF) by in-situ growing 2D cobalt vanadium layered double hydroxide (CoV-LDH) vertically on 2D few-layered V2CTx MXene nanosheets and interconnecting it with Ni foam (NF) with a self-supported structure to act as a binder-free electrode. In addition to inhibiting CoV-LDH aggregation, the highly conductive V2CTx MXene and CoV-LDH work synergistically to improve charge storage. The specific capacitance of the TMA-V2CTx/CoV-LDH/NF electrode is 2374 F/g (1187 C/g) at 1 A/g. At the same time, the TMA-V2CTx/CoV-LDH/NF exhibits excellent stability, retaining 85.3 % of its specific capacitance at 20 A/g after 10,000 cycles. In addition, the hybrid supercapacitor (HSC) is assembled based on positive electrode (TMA-V2CTx/CoV-LDH/NF) and negative electrode (AC), achieving the maximum energy density of 74.4 Wh kg-1 at 750.3 W kg-1. TMA-V2CTx/CoV-LDH/NF has potential as an electrode material for storing green energy. The research strategy provides a development prospect for the construction of novel V2CTx MXene-based electrode material with self-supported structures.

Tannic acid - a bridge and suspending agent for lithium cobalt oxide and reduced graphene oxide: a lodestar for lithium-ion batteries

ABSTRACTLithium cobalt oxide (LCO) has been employed as cathode material for 40 years. However, the low solubility of LCOs in water and strong electrostatic force and H-bonding between the LCOs particles limited the use of the aqueous binders in the LCO system. We report a feasible and universal approach to fabricating a complex cathode of LCO and reduced graphene oxide (RGO). Tannic acid (TA) could simultaneously disperse LCO and RGO particles. Meanwhile, the branched polyphenol TA acts as a 'bridge' molecule for connecting the LCO and RGO, confirmed by the SEM test. The rheology properties of the PVDF slurry of cathode materials (LCO, LCO/, RGO, and TA/LCO/RGO) were also determined. It could be found that the TA could act as a crosslinking agent for the LCO and RGO particles, increasing the viscosity and storage modulus of the slurry. The cell employed the TA/LCO/RGO slurry as the cathode material, have a higher areal capacity, and had a higher redox potential than employed LCO/RGO and LCO as cathode materials, all of which could be attributed to the addition of the TA. This green molecule can be used to fabricate environmentally friendly and possibly biodegradable electrochemical energy storage devices.

N/S Co-Doped Graphene Aerogels as Superior Anode Materials for High-Rate Lithium-Ion Batteries

The nitrogen and sulfur co-doped graphene aerogel (SNGA) was synthesized by a one-pot hydrothermal route using graphene oxide as the starting material and thiourea as the S and N source. The obtained SNGA with a three-dimensionally hierarchical structure, providing more available pathways for the transport of lithium ions. The existing form of S and N was regulated by changing the calcination temperature and thiourea doping amount. The results revealed that high temperature could decompose -SOX- functional groups and promote the transformation of C-S-C to C-S, ensuring the cyclic stability of electrode materials, and increasing the thiourea dosage amount introduced more pyridine nitrogen, improving the multiplicative performance of electrode materials. Benefiting from the synergistic effect of sulfur and nitrogen atoms, the prepared SNGA showed superior rate capability (107.8 mAh g-1 at 5 A g-1), twice more than that of GA (52.8 mAh g-1), and excellent stability (232.1 mAh g-1 at 1 A g-1 after 300 cycles), 1.85 times more than that of GA (125.6 mAh g-1). The present study provides a detailed report on thiourea as a dopant to provide a sufficient basis for SNGA and a theoretical guide for further modifying.

MXene-based anode materials for high performance sodium-ion batteries

As an emerging class of layered transition metal carbides/nitrides/carbon-nitrides, MXenes have been one of the most investigated anode subcategories for sodium ion batteries (SIBs), due to their unique layered structure, metal-like conductivity, large specific surface area and tunable surface groups. In particular, different MAX precursors and synthetic routes will lead to MXenes with different structural and electrochemical properties, which actually gives MXenes unlimited scope for development. In this feature article, we systematically present the recent advances in the methods and synthetic routes of MXenes, together with their impact on the properties of MXenes and also the advantages and disadvantages. Subsequently, the sodium storage mechanisms of MXenes are summarized, as well as the recent research progress and strategies to improve the sodium storage performance. Finally, the main challenges currently facing MXenes and the opportunities in improving the performance of SIBs are pointed out.

Preparation of carbon-coated Fe2 O3 @Ti3 C2 Tx composites by mussel-like modifications as high-performance anodes for lithium-ion batteries

Fe2 O3 with high theoretical capacity (1007 mA h g-1 ) and low cost is a potential anode material for lithium-ion batteries (LIBs), but its practical application is restricted by its low electrical conductivity and large volume changes during lithiation/delithiation. To solve these problems, Fe2 O3 @Ti3 C2 Tx composites were synthesized by a mussel-like modification method, which relies on the self-polymerization of dopamine under mild conditions. During polymerization, the electronegative group (-OH) on dopamine can easily coordinate with Fe3+ ions as well as form hydrogen bonds with the -OH terminal group on the surface of Ti3 C2 Tx , which induces a uniform distribution of Fe2 O3 on the Ti3 C2 Tx surface and mitigates self-accumulation of MXene nanosheets. In addition, the polydopamine-derived carbon layer protects Ti3 C2 Tx from oxidation during the hydrothermal process, which can further improve the electrical conductivity of the composites and buffer the volume expansion and particle agglomeration of Fe2 O3 . As a result, Fe2 O3 @Ti3 C2 Tx anodes exhibit ~100 % capacity retention with almost no capacity loss at 0.5 A g-1 after 250 cycles, and a stable capacity of 430 mA h g-1 at 2 A g-1 after 500 cycles. The unique structural design of this work provides new ideas for the development of MXene-based composites in energy storage applications.

Waste biomass garlic stem-derived porous carbon materials as high-capacity and long-cycling anode for lithium/sodium-ion batteries

Carbon materials are promising anode materials for rechargeable lithium and sodium-ion batteries, due to their low cost, high capacity, and structural designability. In this work, we selected a waste biomass, garlic stem, as the carbon precursor, and we systematically investigated the effect of pyrolysis temperature and time on their battery performance. We find that 800 °C and 2 h are the best pyrolysis conditions, which leads to the optimal carbon material (800C-2H) with a large layer spacing, abundant defect sites, high surface area, and sufficient micro/meso-porous structures. Due to these favorable properties, this carbon anode exhibits an impressive performance for Lithium-ion batteries, with a very high capacity of 480 mAh g-1 and no significant capacity fading after 3000 cycles. Besides, this anode also shows promising performance for Sodium-ion batteries, where a good capacity of 151.9 mAh g-1 and reasonable cycling of 100 cycles are achievable. We also carried out in-situ X-ray diffraction and in-situ Raman spectroscopy experiments to understand the relationship between carbon microstructures and their Li-ion storage.

NiM (Sb, Sn)/N-doped hollow carbon tube as high-rate and high-capacity anode for lithium-ion batteries

Alloy-type materials are regarded as prospective anode replacements for lithium-ion batteries (LIBs) owing to their attractive theoretical capacity. However, the drastic volume expansion leads to structural collapse and pulverization, resulting in rapid capacity decay during cycling. Here, a simple and scalable approach to prepare NiM (M: Sb, Sn)/nitrogen-doped hollow carbon tubes (NiMC) via template and substitution reactions is proposed. The nanosized NiM particles are uniformly anchored in the robust hollow N-doped carbon tubes via NiNC coordination bonds, which not only provides a buffer for volume expansion but also avoids agglomerating of the reactive material and ensures the integrity of the conductive network and structural framework during lithiation/delithiation. As a result, NiSbC and NiSnC exhibit high reversible capacities (1259 and 1342 mAh/g after 100 cycles at 0.1 A/g) and fascinating rate performance (627 and 721 mAh/g at 2 A/g), respectively, when employed as anodes of LIBs. The electrochemical kinetic analysis reveals that the dominant lithium storage behavior of NiMC electrodes varies from capacitive contribution to diffusion contribution during the cycling corresponding to the activation of the electrode exposing more NiM sites. Meanwhile, M (Sb, Sn) is gradually transformed into stable NiM during the de-lithium process, making the NiMC structure more stable and reversible in the electrochemical reaction. This work brings a novel thought to construct high-performance alloy-based anode materials.

Application of MXene-Based Materials for Cathode in Lithium-Sulfur Batteries

The lithium-sulfur (Li-S) batteries have a high theoretical specific capacity of 1675 mAh ⋅ g-1 and have become the most promising high-energy storage system for the next generation batteries technology. However, their applications are hindered by insulated feature and volume expansion of sulfur, as well as the "shuttle effect" of polysulfides. MXenes own metallic conductivity and strong ability of polysulfides adsorption. Besides, their unique two-dimensional (2D) structure, large specific surface area, abundant functional groups, and adjustability are beneficial to overcome the drawbacks of the sulfur cathode. In this review, different mainstream preparation methods and excellent properties of MXenes are summarized. Significant achievements and recent progress of MXene-based cathodes and interlayers applied to Li-S cathodes are concluded later. Finally, the challenges, possible solutions and potential applications of MXenes for Li-S batteries are also presented.

Interface regulation of Zr-MOF/Ni2P@nickel foam as high-efficient electrocatalyst for pH-universal hydrogen evolution reaction

Currently, the development of economical and effective non-noble metal electrocatalysts is vital for advancing hydrogen evolution reaction (HER) and enabling its widespread applications. The customizable pore structure and enormous surface area of metal-organic frameworks (MOFs) have made them to become promising non-noble metal electrocatalysts for HER. However, MOFs have some challenges, including low conductivity and instability, which can result in them having high overpotentials and slow reaction kinetics in electrocatalytic processes. In this work, we present an innovative approach for synthesizing cost-effective and high-efficient Zr-MOF-derived pH-universal electrocatalysts for HER. It entails creating the interfaces of the electrocatalysts with suitable proportions of phosphide nanostructures. Zr-MOF/Ni2P@nickel foam (NF) electrodes with interface regulated by Ni2P nanostructures were successfully developed for high-efficient pH-universal HER electrocatalysts. The presence of Ni2P nanostructures with abundant active sites at the Zr-MOFs@NF interfaces boosted the electronic conductivity and local charge density of the hybrid electrocatalysts. This helped to improve their reaction kinetics and electrocatalytic activity. By optimizing the Ni2P amount, Zr-MOF/Ni2P@NF demonstrated impressive stability and superior HER activities, with a low overpotential of 149 mV (acidic electrolytes) and 143 mV (alkaline electrolytes) at 10 mA cm-2. The proven strategy in this work can be expanded to many types of MOF-based materials for wider practical applications.

One-step construction of hexagonal WO3 nano-shuttles with enhanced lithium storage performance

In this work, WO3 nanorod-based aggregates and WO3 nano-shuttles were constructed by a facile hydrothermal route. The structure, morphology, element composition and valence state of the formed WO3 samples were characterized using different testing instruments. As the active anode for lithium-ion batteries, the WO3 nano-shuttle electrode can deliver a reversible specific capacity of 614.7 mA h g-1 after 300 cycles at a current density of 500 mA g-1. The excellent electrochemical properties indicate that WO3 nano-shuttles are a prospective anode candidate for high performance lithium-ion batteries.

V4 C3 MXene Immune Profiling and Modulation of T Cell-Dendritic Cell Function and Interaction

Although vanadium-based metallodrugs are recently explored for their effective anti-inflammatory activity, they frequently cause undesired side effects. Among 2D nanomaterials, transition metal carbides (MXenes) have received substantial attention for their promise as biomedical platforms. It is hypothesized that vanadium immune properties can be extended to MXene compounds. Therefore, vanadium carbide MXene (V4 C3 ) is synthetized, evaluating its biocompatibility and intrinsic immunomodulatory effects. By combining multiple experimental approaches in vitro and ex vivo on human primary immune cells, MXene effects on hemolysis, apoptosis, necrosis, activation, and cytokine production are investigated. Furthermore, V4 C3 ability is demonstrated to inhibit T cell-dendritic cell interactions, evaluating the modulation of CD40-CD40 ligand interaction, two key costimulatory molecules for immune activation. The material biocompatibility at the single-cell level on 17 human immune cell subpopulations by single-cell mass cytometry is confirmed. Finally, the molecular mechanism underlying V4 C3 immune modulation is explored, demonstrating a MXene-mediated downregulation of antigen presentation-associated genes in primary human immune cells. The findings set the basis for further V4 C3 investigation and application as a negative modulator of the immune response in inflammatory and autoimmune diseases.

Preparation and Evaluation of Co-Doped Fe7S8/C Composites for Lithium Storage

Fe₇S₈ has a high theoretical capacity (663 mAh g^-1) and can be prepared at a low cost, making it advantageous for production. However, Fe₇S₈ has two disadvantages as a lithium-ion battery anode material. The first is that the conductivity of Fe₇S₈ is not good. The second is that when the lithium ion is embedded, the volume expansion of the Fe₇S₈ electrode is serious. That is why Fe₇S₈ has not been used in real life yet. In this paper, Co-Fe₇S₈/C composites were prepared by doping Co into Fe₇S₈ through a one-pot simple hydrothermal method. In situ Co is doped into Fe₇S₈ to produce a more disordered microstructure to improve ion and electron transport performance, thereby reducing the activation barrier of the main material. The Co-Fe₇S₈/C electrode presents a high specific discharge capacity of 1586 mAh g^-1 and a Coulombic efficiency (CE) of 71.34% at an initial cycle at 0.1 A g^-1. After 1500 cycles, the specific discharge capacity remains at 436 mAh g^-1 (5 A g^-1). When the current density returns to 0.1 A g^-1, the capacity almost returns to the initial level, showing excellent rate performance.

A moisture self-regenerative, ultra-low temperature anti-freezing and self-adhesive polyvinyl alcohol/polyacrylamide/CaCl2/MXene ionotronics hydrogel for bionic skin strain sensor

Ignited by the concept of bionics, hydrogel-based bionic skin sensors have received more and more attention and been widely used in health monitoring, robots, implantable prostheses and human-machine interfaces. However, there still remain some challenges to be urgently solved for hydrogel-based bionic skin sensors, such as the water evaporation and the defects of single conductive mechanism of electronic skin or ionic skin. Herein, we prepared a polyvinyl alcohol/polyacrylamide/CaCl₂/MXene (PPCM) ionotronics hydrogel with moisture self-regenerative, highly sensitive, ultra-low temperature anti-freezing (-50 °C) and self-adhesive features and applied it as bionic skin strain sensor. The introduction of MXene and CaCl₂ endows the PPCM hydrogel with both electron and ion conductive channels, which effectively compensates for the defects of single electronic skin or ionic skin. Importantly, the addition of CaCl₂ into the PPCM hydrogel offers it the moisture self-regenerative ability, holding the long-term water retention. The water in the PPCM hydrogel can still be kept in a stable state after continuous use for 70 days at room temperature, thus ensuring the long-term stability of the hydrogel-based sensor. Such a moisture self-regenerative ability should be an important feature for intelligentizing the hydrogel-based bionic skin for practical applications.

Sodium titanium phosphate nanocube decorated on tablet-like carbon for robust sodium storage performance at low temperature

Sodium-ion batteries, featuring resource abundance and similar working mechanisms to lithium-ion batteries, have gained extensive interest in both scientific exploration and industrial applications. However, the extremely sluggish reaction kinetics of charge carrier (Na+) at subzero temperatures significantly reduces their specific capacities and cycling life. Herein, this study presents a novel hybrid structure with sodium titanium phosphate (NaTi2(PO4)3, NTP) nanocube in-situ decorated on tablet-like carbon (NTP/C), which manifests superior sodium storage performances at low temperatures. At even -25 °C, a stable cycling with a specific capacity of 94.3 mAh/g can still be maintained after 200 cycles at 0.5 A/g, delivering a high capacity retention of 91.5 % compared with that at room temperature, along with an excellent rate capability. Generally, the superionic conductor structure, flat voltage plateaus, as well as the conductive carbonaceous framework can efficiently facilitate the charge transfer, accelerate the diffusion of Na+, and decrease the electrochemical polarization. Moreover, further investigations on diffusion kinetics, solid electrolyte interface layer, and the interaction between NTP and carbonaceous skeleton reveal its high Na+ diffusion coefficient, robust solid electrolyte interface, and strong electronic interaction, thus contributing to the superior capacity retentions at subzero temperatures.

Advances of MXenes; Perspectives on Biomedical Research

The last decade witnessed the emergence of a new family of 2D transition metal carbides and nitrides named MXenes, which quickly gained momentum due to their exceptional electrical, mechanical, optical, and tunable functionalities. These outstanding properties also rendered them attractive materials for biomedical and biosensing applications, including drug delivery systems, antimicrobial applications, tissue engineering, sensor probes, auxiliary agents for photothermal therapy and hyperthermia applications, etc. The hydrophilic nature of MXenes with rich surface functional groups is advantageous for biomedical applications over hydrophobic nanoparticles that may require complicated surface modifications. As an emerging 2D material with numerous phases and endless possible combinations with other 2D materials, 1D materials, nanoparticles, macromolecules, polymers, etc., MXenes opened a vast terra incognita for diverse biomedical applications. Recently, MXene research picked up the pace and resulted in a flood of literature reports with significant advancements in the biomedical field. In this context, this review will discuss the recent advancements, design principles, and working mechanisms of some interesting MXene-based biomedical applications. It also includes major progress, as well as key challenges of various types of MXenes and functional MXenes in conjugation with drug molecules, metallic nanoparticles, polymeric substrates, and other macromolecules. Finally, the future possibilities and challenges of this magnificent material are discussed in detail.

Element-Doped Mxenes: Mechanism, Synthesis, and Applications

Heteroatom doping can endow MXenes with various new or improved electromagnetic, physicochemical, optical, and structural properties. This greatly extends the arsenal of MXenes materials and their potential for a spectrum of applications. This article comprehensively and critically discusses the syntheses, properties, and emerging applications of the growing family of heteroatom-doped MXenes materials. First, the doping strategies, synthesis methods, and theoretical simulations of high-performance MXenes materials are summarized. In order to achieve high-performance MXenes materials, the mechanism of atomic element doping from three aspects of lattice optimization, functional substitution, and interface modification is analyzed and summarized, aiming to provide clues for developing new and controllable synthetic routes. The mechanisms underlying their advantageous uses for energy storage, catalysis, sensors, environmental purification and biomedicine are highlighted. Finally, future opportunities and challenges for the study and application of multifunctional high-performance MXenes are presented. This work could open up new prospects for the development of high-performance MXenes.

Electronic and Optical Properties of Twin T-Graphene Co-Doped with Boron and Phosphorus

Twin T-graphene (TTG) is a new two-dimensional carbon allotrope of graphene. Heteroatom co-doping is an effective method for the modulation of the physical and chemical properties of two-dimensional materials. This study explored the structural stability, electronic structures, and optical properties of boron and phosphorus co-doped TTG using first-principles calculations. TTG was doped with B and P atoms (BP) at different positions considering 13 different configurations. Pristine TTG has a band gap of 1.89 eV, and all BP co-doped TTG (TTG/BP) systems remain semiconducting with band gaps that gradually decrease with increasing doping concentration. For a given doping concentration, the TTG/BP-ortho systems had a narrower band gap than the corresponding TTG/BP-para systems. The TTG and TTG/BP systems exhibited significant optical anisotropy. In the infrared region, BP co-doping increased the absorption coefficient, and the reflectance and refractive index increased with increasing doping concentration, except for the vertical component of the TTG/BP-ortho system. In the visible region, the absorption coefficient, reflectance, and refractive index decreased with increasing doping concentration for the vertical component, and the peaks were red-shifted from the near-ultraviolet region to the visible region. In the near-ultraviolet region, the reflectance also decreased with increasing doping concentration. The BP co-doping concentration can regulate the electronic structures and optical properties of the TTG, showing that the BP co-doped TTG has potential for application in nanoelectronics and optoelectronics.

Highly reversible Li-ion full batteries using a Mg-doped Li-rich Li1.2Ni0.28Mn0.468Mg0.052O2 cathode and carbon-decorated Mn3O4 anode with hierarchical microsphere structures

Microsphere structured Mg-doped Li-rich Li1.2Ni0.28Mn0.468Mg0.052O2 cathode and carbon-decorated Mn3O4 anode materials were prepared for application to lithium-ion full batteries. As-assembled lithium-ion full batteries exhibited enhanced electrochemical performances like high charge/discharge capacity, and long-term capacity retention.

A nano-truncated Ni/La doped manganese spinel material for high rate performance and long cycle life lithium-ion batteries

A nano-truncated octahedral LiNi0.08La0.01Mn1.91O4 cathode material with {111} and {100} crystal planes achieves capacity retention of 89.0% after 1000 cycles at 10C.

Improved electrode kinetics of a modified Na3V2(PO4)3 cathode through Zr substitution and nitrogen-doped carbon coating towards robust electrochemical performance at low temperature

The substitution of V with Zr in a NASICON structure and an NC coating endow 0.1Zr-NVP/NC with excellent electrochemical performance at low temperature.

Boosting the lithium storage performance by synergistically coupling ultrafine heazlewoodite nanoparticle with N, S co-doped carbon

Transition metal sulfides, as an important class of inorganics, have been shown to be potential high-performance electrode candidates for lithium-ion batteries (LIBs) in account of their high activity towards lithium storage, rich types and diverse structures. Despite these advantages, structure degradation related with volume variations upon electrochemical cycling restricts their further development. In this present study, a unique hybrid structure with ultrafine heazlewoodite nanoparticles (less than 10 nm) in-situ confined in nitrogen and sulfur dual-doped carbon (Ni₃S₂@NSC) was constructed though a facile pyrolysis process, using a novel Ni-based metal chelates as the precursor. Specifically, enhanced structure stability, shortened Li⁺ migration distance and improved reaction dynamics can be obtained simultaneously in the designed structure, thereby allowing to realize high lithium storage performance. Consequently, a remarkable reversible capacity of 955.9 mAh g^-1 (0.1 A g^-1 after 100 cycles) and a superior long-term cycling stability up to 1200 cycles (863.7 mAh g^-1 at 1.0 A g^-1) are obtained. Importantly, the fundamental understanding on the improved lithium storage of Ni₃S₂@NSC based on the synergistic coupling reveals that the combination between Ni₃S₂ and NSC at the hetero-interface through the doped sulfur atoms contributes to the integrity of electrode and improved kinetics.

In Situ Preparation of MXenes in Ambient-Temperature Organic Ionic Liquid Aluminum Batteries with Ultrastable Cycle Performance

A fluorine-free and water-free electrochemical preparation of MXenes is achieved in Lewis acidic molten salts at ambient temperature. In addition, the anode reaction of the MAX phase V₂AlC is studied in the organic ionic liquid aluminum battery and the extraction voltages of the metal atoms Al and V in the MAX phase V₂AlC are determined. This points out the direction for the constant-voltage electrochemical preparation of MXenes. Furthermore, the electrochemical performance of the etched V₂AlC (E-V₂AlC) in an aluminum battery is studied. The one-stop preparation-application process prevents the MXenes from contacting water and air, and the MXenes etched in the aluminum battery are more conducive to the intercalation/deintercalation of Al³⁺. Therefore, E-V₂AlC exhibits excellent electrochemical performance in an aluminum battery. Under the conditions of a voltage window of 0.01-2.3 V (V vs Al/Al³⁺) and a current density of 500 mA g^-1, the specific discharge capacity is about 100 mAh g^-1 after 6500 cycles. In addition, the energy storage mechanism and Faraday energy storage method of E-V₂AlC in an aluminum battery are studied. The diffusion coefficient D of Al³⁺ is determined by a galvanostatic intermittent titration technique. The reasons for its excellent electrochemical performance are clarified from the perspective of kinetics.

Ultra-Stable Potassium Ion Storage of Nitrogen-Doped Carbon Nanofiber Derived from Bacterial Cellulose

As a promising energy storage system, potassium (K) ion batteries (KIBs) have received extensive attention due to the abundance of potassium resource in the Earth's crust and the similar properties of K to Li. However, the electrode always presents poor stability for K-ion storage due to the large radius of K-ions. In our work, we develop a nitrogen-doped carbon nanofiber (N-CNF) derived from bacterial cellulose by a simple pyrolysis process, which allows ultra-stable K-ion storage. Even at a large current density of 1 A g-1, our electrode exhibits a reversible specific capacity of 81 mAh g-1 after 3000 cycles for KIBs, with a capacity retention ratio of 71%. To investigate the electrochemical enhancement performance of our N-CNF, we provide the calculation results according to density functional theory, demonstrating that nitrogen doping in carbon is in favor of the K-ion adsorption during the potassiation process. This behavior will contribute to the enhancement of electrochemical performance for KIBs. In addition, our electrode exhibits a low voltage plateau during the potassiation-depotassiation process. To further evaluate this performance, we calculate the "relative energy density" for comparison. The results illustrate that our electrode presents a high "relative energy density", indicating that our N-CNF is a promising anode material for KIBs.