Theoretical Storage Capacity Research Articles

Two-dimensional Zr2C monolayer as anode material for Li, Na and K ion batteries

In this paper, the electronic properties and storage capacity of Zr2C after adsorption of Li, Na, and K metal ions are systematically investigated with density-functional theory (DFT) based on first-principles calculations. For Li, Na, and K ion adsorption, the negative adsorption energy indicates a strong interaction between the metal ions and the two-dimensional (2D) Zr2C monolayer, which prevents the formation of dendrites, and the adsorbed system has good metallic properties with low diffusion barriers, suitable open-circuit voltages, and high theoretical storage capacities. Our study shows that Zr2C monolayer is a promising anode material for metal-ion batteries.

Suitability of BC6N monolayer as an anode material for K-ions batteries: A first-principles study

Selecting an appropriate anode material is a crucial initial stage in improvement of batteries to achieve optimal performance. This study investigates suitability of BC6NA monolayer as an anode through application of first-principles based DFT. With varying K atom adsorption concentrations, the BC6NA monolayer maintains its metallic behaviors, which is a great asset for battery purposes. A theoretical storage capacity for K-adsorbed BC6NA monolayer of 390.52 mAhg−1 has been presented, which is a significant improvement over graphite, BC6NA, and many other 2D materials. K-ions on the BC6NA monolayer and a reliable diffusion barrier of 0.35 eV point to good diffusivity. Open-circuit voltage (OCV) is moderate and lower than for materials used in traditional anodes. According to our findings, the BC6NA monolayer can serve as an effective host material for K-ions batteries (KIBs). As a result, the current research into the possible anodic use of BC6NA monolayer is beneficial for next experimental work on sodium storage methods for KIBs.

SiP2 monolayer as potential anode material for Na/K-ion batteries predicted from first-principles calculations

Based on the density functional theory (DFT), a systematic feasibility analysis of monolayer SiP2 as potential anode material for Na/K-ion batteries has been carried out. Through ab-initio molecular dynamics (AIMD) calculation, the findings reveal exceptional stability of SiP2. The ultra-low ion diffusion barriers (0.107 eV for Na and 0.043 eV for K) and metallic properties following adsorption of alkali metal ions demonstrate that SiP2 exhibits a rapid charge and discharge rate and remarkable electrical conductivity when employed as an anode. Furthermore, it possesses a considerable theoretical storage capacity (Na/K: 446.53/595.38 mAh/g) and energy density (Na/K: 1026.91/1322.46 mWh/g). These findings suggest that monolayer SiP2 exhibits superior performance as potential anode material for Na/K-ion batteries.

Strain Engineering of ScYCCl2 MXene Monolayer and Intercalation of Metal-ions on MXene Surface: A DFT Study

The present work theoretically examines the influence of bi-axial strain on functionalized ScYCCl2 monolayer. The indirect to direct band gap transition on tensile conditions and the phase transition from semiconductor to metal on compressive strain have been studied. The analysis of extreme conditions of 10% compressive and 10% tensile strain through phonon and AIMD simulations underscore the kinetic and thermal stability, respectively of the monolayer under strain. These findings assure the possibility of experimental synthesis of the ScYCCl2 monolayer. After metallization, ScYCCl2 MXene is used as an anode of metal-ion (−Na, −K, −Li, −Mg) batteries as it has high theoretical storage capacity and low open circuit voltage. Work function engineering and the strain-dependent optical behavior of the ScYCCl2 monolayer have been examined. The work function of the ScYCCl2 monolayer has been raised under compressive strain and decreased under tensile strain. The Crystal Orbital Hamiltonian Population has been simulated under tensile and compressive strain to check the bond- strengths. Hence, the ScYCCl2 monolayer has the capability to alter its characteristics under strain. The improved optical characteristics recommend its applications in low-dimensional photonic devices and metallization after compressive strain recommends its energy storage applications in metal-ion batteries.

Enhancing Electrochemical Performance of Si@CNT Anode by Integrating SrTiO3 Material for High-Capacity Lithium-Ion Batteries

Silicon (Si) has attracted worldwide attention for its ultrahigh theoretical storage capacity (4200 mA h g−1), low mass density (2.33 g cm−3), low operating potential (0.4 V vs. Li/Li+), abundant reserves, environmentally benign nature, and low cost. It is a promising high-energy-density anode material for next-generation lithium-ion batteries (LIBs), offering a replacement for graphite anodes owing to the escalating energy demands in booming automobile and energy storage applications. Unfortunately, the commercialization of silicon anodes is stringently hindered by large volume expansion during lithiation–delithiation, the unstable and detrimental growth of electrode/electrolyte interface layers, sluggish Li-ion diffusion, poor rate performance, and inherently low ion/electron conductivity. These present major safety challenges lead to quick capacity degradation in LIBs. Herein, we present the synergistic effects of nanostructured silicon and SrTiO3 (STO) for use as anodes in Li-ion batteries. Si and STO nanoparticles were incorporated into a multiwalled carbon nanotube (CNT) matrix using a planetary ball-milling process. The mechanical stress resulting from the expansion of Si was transferred via the CNT matrix to the STO. We discovered that the introduction of STO can improve the electrochemical performance of Si/CNT nanocomposite anodes. Experimental measurements and electrochemical impedance spectroscopy provide evidence for the enhanced mobility of Li-ions facilitated by STO. Hence, incorporating STO into the Si@CNT anode yields promising results, exhibiting a high initial Coulombic efficiency of approximately 85%, a reversible specific capacity of ~800 mA h g−1 after 100 cycles at 100 mA g−1, and a high-rate capability of 1400 mA g−1 with a capacity of 800 mA h g−1. Interestingly, it exhibits a capacity of 350 mAh g−1 after 1000 lithiation and delithiation cycles at a high rate of 600 mA hg−1. This result unveils and sheds light on the design of a scalable method for manufacturing Si anodes for next-generation LIBs.

Influence of cationic species on the electrochemical performance of quinone derivatives

Quinones exhibit considerable promise as active components in energy storage applications, owing to their high theoretical storage capacity, well-defined redox potentials, rapid reaction kinetics, structural diversity, and proficiency in cycling both protons and metal ions. In this study, six quinone derivatives underwent comprehensive electrochemical and computational analyses using TBA+, H+, Li+, K+, Na+, Ca2+, and Mg2+-based electrolytes, aiming to uncover novel cycling chemistries with organic materials. Cyclic Voltammetry (CV) and Square Wave Voltammetry (SWV) elucidated the widely recognized 2H+/2e- redox process during proton cycling, as well as the two-step 1e- redox process in the presence of other cycling ions. Additionally, it was established that the quinone formal redox potential for different cycling chemistries followed the sequence TBA+ < K+ < Na+ < Li+ < H+, and cycling of the divalent cations resulted in potentials within the same range as those observed for proton cycling. DFT calculations provided insights into how cycling ions influenced the quinone formal redox potential, attributing it to the cation's ability to accommodate a portion of the bisolate anion charge upon reduction. Cations inducing a higher quinone formal redox potential and accommodating a larger fraction of the negative charge demonstrated a greater stabilizing effect on the reduced state. This stabilizing effect exhibited a strong correlation with the ionization energies of the respective cations.

BC6NA monolayer as an ideal anode material for high-performance sodium-ion batteries

Selecting an appropriate anode material (AM) has been considered to be a crucial initial step in advancing high-performance batteries. Within this piece of research, we examine the suitability of the BC6NA monolayer (referred to as BC6NAML) as an AM by first-principles calculations. The BC6NAML exhibits metallic behavior consistently, even with varying concentrations of Na atoms, making it an ideal choice for battery usages. Our findings revealed that the theoretical storage capacity for Na-adhered BC6NAML was 406.36 mAhg−1, surpassing graphite, TiO2, BC6NA, and numerous other 2D materials. The BC6NAML also demonstrates a diffusion barrier of 0.39 eV and favorable diffusivity of Na-ions. Although the open-circuit voltage (OCV) of BC6NAML was temperate and lower compared to the OCV of other AMs like TiO2, our results suggested that it is possible to utilize BC6NAML as one of the encouraging host materials for sodium-ion batteries (SIBs). Consequently, this investigation into the potential anodic application of BC6NAML proves valuable for future experimental studies into sodium storage for SIBs.

Theoretical prediction of SbP3 monolayer as anode material for lithium-ion battery applications

Herein, we have carried out a systematic investigation using first-principles calculations on the properties of Li atoms adsorbed on SbP3 monolayer in order to evaluate its pertinence as an anode material for (LIBs). The diffusion barrier value of Li atom on the SbP3 monolayer is around 0.44 eV, which is quite low. The value of OCV of the SbP3 monolayer is moderate and comparable to the commercial anode materials TiO2. Also, the theoretical storage capacity of Li-ion in SbP3 monolayer is 499.36 mAhg−1. Therefore, these findings render the SbP3 monolayer a potential candidate as an efficient anode material for LIBs.

Enhanced Redox Activity of Anthraquinone on N‐Doped Porous Carbon Electrode

AbstractAnthraquinone is one of the organic molecules that can potentially replace metal‐based electrodes due to its fast and reversible redox reaction as well as the abundance in nature. Here, we reported the redox activity of anthraquinone on N‐doped porous carbon electrodes derived from chemical activation of tea leaves with potassium carbonate. Electrochemical behavior was evaluated by cyclic voltammetry and galvanostatic charge/discharge in sulfuric acid, with X‐ray photoelectron spectroscopy providing insights into the surface chemistry of the electrodes. Anthraquinone on the composite electrode was able to achieve 97 % of its theoretical storage capacity. We found that nitrogen‐containing functional groups, especially graphitic and pyrrolic groups, had a major impact on the enhanced redox activity of anthraquinone.

Fast-Charging Phosphorus-Based Anodes: Promises, Challenges, and Pathways for Improvement.

Fast-charging batteries are highly sought after. However, the current battery industry has used carbon as the preferred anode, which can suffer from dendrite formation problems at high current density, causing failure after prolonged cycling and posing safety hazards. The phosphorus (P) anode is being considered as a promising successor to graphite due to its safe lithiation potential, low ion diffusion energy barrier, and high theoretical storage capacity. Since 2019, fast-charging P-based anodes have realized the goals of extreme fast charging (XFC), which enables a 10 min recharging time to deliver a capacity retention larger than 80%. Rechargeable battery technologies that use P-based anodes, along with high-capacity conversion-type cathodes or high-voltage insertion-type cathodes, have thus garnered substantial attention from both the academic and industry communities. In spite of this activity, there remains a rather sparse range of high-performance and fast-charging P-based cell configurations. Herein, we first systematically examine four challenges for fast-charging P-based anodes, including the volumetric variation during the cycling process, the electrode interfacial instability, the dissolution of polyphosphides, and the long-lasting P/electrolyte side reactions. Next, we summarize a range of strategies with the potential to circumvent these challenges and rationally control electrochemical reaction processes at the P anode. We also consider both binders and electrode structures. We also propose other remaining issues and corresponding strategies for the improvement and understanding of the fast-charging P anode. Finally, we review and discuss the existing full cell configurations based on P anodes and forecast the potential feasibility of recycling spent P-based full cells according to the trajectory of recent developments in batteries. We hope this review affords a fresh perspective on P science and engineering toward fast-charging energy storage devices.

Low diffusion barrier in black phosphorene/graphdiyne heterostructure for ultrafast Li-ion battery anode

Black phosphorene (BlackP) with low diffusion barriers has been extensively researched as one of the new Li-ion batteries (LIBs) anode materials. Nevertheless, the poor mechanical properties and elastic stiffness of BlackP obviously limit its practical application. Thus, owing to the excellent mechanical properties and good elastic stiffness exhibited by Graphdiyne (GDY), the BlackP/GDY Van der Waals (vdW) heterostructure was investigated in our study to overcome those disadvantages on the basis of the density functional theory (DFT). Our results suggest that the BlackP/GDY vdW heterostructure has favorable mechanical properties and high thermodynamic stability with a small lattice mismatch, which is owing to the synergistic effect existed in BlackP and GDY. Besides, the adsorption energy of Li adsorption on the BlackP/GDY vdW heterostructure evidently enhanced along with the changing of the heterostructure from semiconductor to metallic. Moreover, the maximum theoretical storage capacity (384.703 mA h/g) of the BlackP/GDY vdW heterostructure is larger than that of Graphite (372 mA h/g). Above all, the minimum diffusion barrier (0.083 eV) is extremely low, which is vital for achieving ultrafast charge and discharge rates. These favorable advantages suggest that the BlackP/GDY vdW heterostructure is a viable ultrafast LIBs anode material.

Reservoir Static Modelling towards Safe CO2 Storage in Depleted Oil Reservoirs of ‘CRK’ Field, Niger Delta, Nigeria

Geological carbon storage (GCS) is gradually gaining acceptance as the technology of highest repute for the mitigation against greenhouse gas effect. This involves the injection and long-term or permanent storage of carbon dioxide (CO2) in subsurface geological formations. The development of a robust 3D reservoir model then becomes necessary to understand the facies changes and the petrophysical properties distribution of candidate CO2 storage reservoirs. This study attempts the use of static modelling technique to investigate the depleted oil and gas reservoirs of ‘CRK’ field in the Niger Delta sedimentary Basin as a potential CO2 storage site. Using an integrated approach of 3D seismic and a suit of well logs from the study area, two reservoir sands (D10C0 and D6200) were mapped. 3D static modelling of discrete and continuous property distribution of the reservoirs revealed the reservoirs are composed majorly of clean sands with water saturation ranging from 8 to 75%. The average porosity and permeability values are between 20 to 29% and 250 to 890mD respectively. A theoretical storage capacity of 24.85Mt is estimated for the two reservoirs combined, while the median effective storage capacity is 6.22Mt. Comparison of the results obtained in the study with recommended standard values show the reservoirs are suitable for CO2 storage. The property models constructed can serve as primary input for dynamic simulation of the oilfield in future studies.

A conceptual CO2 fill-and-spill mega-fairway in the UK Southern North Sea: A new approach to identify and optimise large-scale underground carbon storage (CCS)

This work explores the subsurface CO2 storage potential in UKCS Quadrants 43–44, by integrating 3D seismic interpretation, regional wellbore data and CO2 migration modelling. We show 11 Bunter Sandstone domes linked together in a fill-and-spill “Bunter Mega-Fairway”. These traps host a theoretical storage capacity of 8.4 Gt CO2 (≈3–4 times the filled-to-spill theoretical capacity of the proposed Endurance storage site), while lessening CO2 leakage risks.Within the mega-fairway, the Triassic Bunter Sandstone reservoir shows a P10-P90 thickness of 78–219 m, along with moderate-high porosities (11–28 %) and permeabilities (9–669 mD). A regionally-connected reservoir is suggested from spatially consistent, near-hydrostatic aquifer pressure gradients (≈0.51 psi/ft). The top-seal is laterally effective and structural closures are lower than the CO2 columns necessary to breach the seal.At the mega-fairway storage depths, CO2 would inhabit the reservoir as a supercritical fluid, enabling it to naturally migrate buoyantly from one trap to another, away from strategically-placed injector sites. Through the integration of migration spill-point modelling, multi-physics seabed monitoring nodes and fill-and-spill injection management, the maximum storage capacity could be achieved, while alleviating CO2 leakage hazards and potentially decreasing the number of injector wells.Exploiting fill-and-spill fairways for CCS is a new concept with vast worldwide applicability.

Deciphering fast lithium storage kinetics via R-based self-derivation effects in siloxanes

Silicon oxycarbide (SiOC) is regarded as a promising anode material for lithium-ion batteries. However, the effect of SiOC's structural composition on lithium-ion storage behaviors, especially the controllable introduction of free carbon (Cfree) and its influence on electrochemical performance, remains a critical challenge that needs to be solved. In this study, based on our finding that the R-based functional group (composed exclusively of carbon and hydrogen atoms) in R-based triethoxysilane can be derived to carbon radicals through thermal decomposition, and then generates Cfree phases into SiOC, we propose a novel concept of R-based self-derivation effects in siloxanes to achieve controlled Cfree introduction for the SiOC anode material. SiOC spheres with tailored structural compositions and Cfree contents are subsequently prepared using a facile and scalable polymeric precursor method, and the effect of Cfree of SiOC spheres on lithium-ion storage performance is studied in combination with density functional theory calculations, revealing that higher Cfree content significantly enhances the lithium-ion storage kinetics of SiOC anode via constructing ion/electron migration “highways”. Notably, SiOC with a high Cfree content up to 37.5 wt% displays excellent lithium-ion storage capability, with a theoretical storage capacity of up to 1004 mAh g−1 and achieving a high reversible capacity of 453 mAh g−1 after 200 cycles at 0.5 A g−1.

A novel two-dimensional whorled CrB4 and MoB4 as high-performance anode material for metal ion batteries

Finding high-storage-capacity anode materials has been a focus of ion-battery research. Two-dimensional (2D) materials have shown promise as high-performance electrode-materials as they have developed gradually. Here we examined the viability of 2D CrB4 and MoB4 monolayers as optimal anode-materials for Li/Na/K ion batteries using first-principles DFT calculations. Preliminary investigations showed that both materials exhibited thermodynamic, structural, and mechanical stability. We found thata strongly negative adsorption energy can help instabilizingthe adsorption of metal-ions on materials surface instead of clustering, that ensures metal-ion-batteries stability. The maximum theoretical storage capacities of Li, Na, and K ions adsorbed on the CrB4 monolayer surface were 1689,1126 and 750 mA h g−1, respectively, while those on the surface of MoB4 were 1155,770 and 513 mA h g−1, respectively. Additionally, calculated open-circuit voltages for Li-ions (0.84,0.82 V), Na-ions (0.25,0.32 V), and K-ions (0.85,0.81 V) for CrB4 and MoB4 monolayers, respectively. Electronic properties showed that increasing the metal ions concentration enhanced both materials’ electrical conductivity and remained the metallic in nature after adsorption. However, Li/Na/K energy barriers are nevertheless consistent with various typical 2D anode materials. The light shaded on 2D MoB4 and CrB4 is anticipated to identify new anode materials for LIBs, NIBs, and KIBs.

Can P3S and C3S monolayers be used as anode materials in metal-ion batteries? An answer from first-principles study.

With the urgent need for efficient energy storage devices, significant attention has been directed to researching and developing promising anode materials for metal-ion batteries. Through density functional study, we successfully predicted the electrochemical performance of P3S and C3S monolayers for the first time, which could be used in alkali metal (Li, Na, and K)-ion batteries. Our study examines the energetic, dynamic, and thermal stabilities of pristine monolayers. The electronic structures of the pristine nanosheets are wide-gap semiconductors. After single metalation on the monolayers, the composite systems become metallic. Charge-density difference (CDD) analysis indicates that charge transfer occurs from alkali metal atoms to the P3S and C3S monolayers, and Bader charge analysis quantifies the amount of charge transfer. We analyzed how readily a single adatom diffuses within the 2D structures. One example is the diffusion of K on C3S, which has a low barrier value of 0.06 eV and seems practically barrierless. Our predicted composite systems report considerable theoretical storage capacity (C); for example, hexalayer K-adsorbed C3S shows a storage capacity of 1182.79 mA h g-1. The estimated open-circuit voltage (OCV) values suggest that the C3S monolayer is a promising anode material for Li-, Na-, and K-ion batteries, whereas the P3S monolayer is suitable as a cathode material for Li-, Na-, and K-ion batteries.

Bismuthene as a novel anode material of magnesium/zinc ion batteries with high capacity and stability: a DFT calculation.

In our research, we utilize density functional theory (DFT) to explore the properties of magnesium and zinc atoms adsorbed on bismuthene. Our findings indicate that the hollow site is the most favorable adsorption site for Mg and Zn atoms on bismuthene. The results indicate that Mg and Zn adsorption on the bismuthene surface results in significantly high conductivity, with notable adsorption energies of -3.38 eV for Mg and -3.91 eV for Zn. The bismuthene structure can adsorb 9 Mg and 18 Zn atoms with negative average adsorption energy. These findings suggest excellent stability of bismuthene during the adsorption of magnesium and zinc. Notably, we propose theoretical storage capacities of 2308 mA h g-1 for magnesium-ion batteries (MgIBs) and 4616 mA h g-1 for zinc-ion batteries (ZnIBs), while maintaining structural stability during the adsorption of these metal ions. The observed average open-circuit voltages for bismuthene are 0.01 V for Mg and 0.03 V for Zn, with the material retaining its metallic properties throughout the adsorption process. Furthermore, the calculated diffusion barriers for Mg and Zn are 0.1 eV and 0.21 eV, respectively. Our findings like storage capacity, diffusion energies, and low OCV surpass those of most studied two-dimensional materials, positioning bismuthene as a promising anode material for metal-ion rechargeable batteries.

Theoretical study of two-dimensional BeB&lt;sub&gt;2&lt;/sub&gt; monolayer as anode material for magnesium ion batteries

&lt;sec&gt;Rechargeable lithium-ion batteries as the main energy storage equipment should possess high power density, excellent reversible capacity, and long cycle life. However, due to the high cost and dendrite growth of Li, searching for non-Li-ion batteries is urgent. Compared with lithium, magnesium has abundant resources, small ionic radius, and high energy density. Therefore, magnesium-ion batteries (MIBs) can serve as the next generation metal-ion batteries. Two-dimensional materials based on Be or B element acting as the anode of metal-ion batteries always exhibit high theoretical storage capacity. Using first-principles calculations, we systematically explore the potential of BeB&lt;sub&gt;2&lt;/sub&gt; as MIBs anode. The optimized BeB&lt;sub&gt;2&lt;/sub&gt; monolayer structure shown in Fig. (a) consists of two atomic layers, where each Be atom is coordinated with six B atoms, and each B atom is coordinated with three Be atoms.&lt;/sec&gt;&lt;sec&gt;The lattice constants are &lt;i&gt;a&lt;/i&gt; = &lt;i&gt;b&lt;/i&gt; = 3.037 Å with a thickness of 0.554 Å. From the phonon spectrum calculations, the absence of imaginary modes indicates the dynamic stability of BeB&lt;sub&gt;2&lt;/sub&gt; monolayer. The presence of a Dirac cone further suggests the excellent conductivity (Fig.(b)). Three stable adsorption sites (Be&lt;sub&gt;1&lt;/sub&gt;: top of Be atoms; Be&lt;sub&gt;2&lt;/sub&gt; and B&lt;sub&gt;2&lt;/sub&gt;: bottom of Be and B atoms) are labeled in Fig. (a). Taking symmetry into account, we consider three pathways to evaluate the migration of Mg atom on BeB&lt;sub&gt;2&lt;/sub&gt; monolayer (Fig.(c)). The corresponding lowest diffusion energy barrier is 0.04 eV along Path III. The stable configuration with the maximum adsorption Mg concentration is shown in Fig.(d), which generates a theoretical capacity of 5250 mA·h·g&lt;sup&gt;–1&lt;/sup&gt;. The calculated average open-circuit voltage is 0.33 V. Based on &lt;i&gt;ab initio&lt;/i&gt; molecular dynamics simulations, the total energy of BeB&lt;sub&gt;2,&lt;/sub&gt; with Mg adsorbed, fluctuates within a narrow range, suggesting that BeB&lt;sub&gt;2&lt;/sub&gt; can sustain structural stability after storing Mg at room temperature (Fig.(e)). Finally, for practical application, we investigate the adsorption and diffusion behavior of Mg on bilayer BeB&lt;sub&gt;2&lt;/sub&gt;. Three configurations are considered: &lt;i&gt;AA&lt;/i&gt; stacking (overlapping of Be atoms in upper layer with Be atoms in lower layer), &lt;i&gt;AB&lt;/i&gt; stacking (overlapping of Be atoms in upper layer with B atoms in lower layer), and &lt;i&gt;AC&lt;/i&gt; stacking (overlapping of Be atoms in upper layer with B—B bonds in lower layer). The most stable configuration is &lt;i&gt;AB&lt;/i&gt; stacking (shown in Fig.(f)) with the interlayer spacing of 3.12 Å and the binding energy of –120.97 meV/atom. Comparing with the BeB&lt;sub&gt;2&lt;/sub&gt; monolayer structure, the adsorption energy of Mg is –2.24 eV for Be&lt;sub&gt;1&lt;/sub&gt;, –1.38 eV for B&lt;sub&gt;5&lt;/sub&gt; site, and –1.90 eV for B&lt;sub&gt;4&lt;/sub&gt; site, while the lowest diffusion energy barrier is 0.13 eV along the path of B&lt;sub&gt;5&lt;/sub&gt;-Be&lt;sub&gt;3&lt;/sub&gt;-B&lt;sub&gt;5&lt;/sub&gt;. Therefore, according to the above-mentioned properties, we believe that BeB&lt;sub&gt;2&lt;/sub&gt; monolayer can serve as an excellent MIBs anode material.&lt;/sec&gt;

First principles study of a triazine-based covalent organic framework as a high-capacity anode material for Na/K-ion batteries.

The rational design of high-performance anode materials is crucial for the development of rechargeable Na-ion batteries (NIBs) and K-ion batteries (KIBs). In this study, based on density functional theory (DFT) calculations, we have systematically investigated the possibility of a bilayer triazine-based covalent organic framework (bilayer TCOF) as an anode for NIBs and KIBs. The calculation of the electronic band structure shows that the bilayer TCOF is a direct band gap semiconductor with a band gap of 2.01 eV. After the adsorption of Na/K at the most favorable sites, the bilayer TCOF transitions from a semiconductor to a metal state, guaranteeing good electronic conductivity. The low diffusion barriers of the bilayer TCOF are 0.45 and 0.26 eV, respectively, indicating a fast diffusion rate of Na/K ions. In addition, the bilayer TCOF has a theoretical storage capacity of up to 628 mA h g-1. Finally, it is found that the average voltage of the bilayer TCOF for NIBs and KIBs is 0.53 and 0.48 V, respectively. Based on these results, we can conclude that the bilayer TCOF may be a suitable anode material for NIBs and KIBs.

A superatom-assembled B8N2 monolayer acting as an electronic sponge for high-capacity anode materials for Na/K-ion batteries.

Rechargeable sodium/potassium-ion batteries (SIBs/PIBs) have emerged as appealing alternatives for lithium-ion batteries due to their earth-abundance and economic benefits. However, exploring high-capacity anode materials for SIBs/PIBs is still challenging. Superatoms with delocalized electronic shells possess high flexibility as electron-acceptors/donors, making them ideal candidates for anode materials. Here, a superatom-assembled boron nitride monolayer (B8N2) was theoretically predicted using first principles calculations. The B8 core is assembled with two B4 superatoms, and further linked by nitrogen atoms in a graphene-like lattice. The B8N2 monolayer has an undirected bandgap (0.82 eV/HSE06) with an ultra-high carrier mobility of 13 × 104 cm2 V-1 s-1, where Na/K ions can be effectively adsorbed on its surface. The remarkably high theoretical storage capacities (924 mA h g-1/1115 mA h g-1), and low open-circuit voltages (0.08 V/0.21 V) are also revealed for the B8N2 monolayer with Na/K ions. Intriguingly, adsorption of Na/K ions causes little geometric deformation of the B8N2 monolayer, which ensures a promising cell operating cycle during the adsorption of Na/K ions at high concentrations. This work reveals the potential of superatoms as an efficient "electronic sponge", providing impetus for the design of superatomic electrode materials for metal ion batteries.