Low Average Open-circuit Voltages Research Articles

BC cone-shaped anodes for lithium-ion batteries

The efficiency of lithium-ion batteries (LIBs) depends upon anode materials possessing high capacity. In present study, we investigate boron carbide cone anode (BCC) for LIBs. The first-principles density functional theory (DFT) method is used to design anode materials based on BCC for application in LIBs. We found that the BCC shows negative Li adsorption energies. Our results also revealed the fast diffusions of Li ion on the BCC with the small energy barrier of 0.34 eV. The storage capacity of BCC system rank among the highest capacity of anodes for LIBs, with value of 785 mAh/g. The low average open-circuit voltage (OCV) value of BCC system indicates that this anode can handle a large operating voltage in LIBs.

TD-graphene: Theoretical prediction of a high-performance anode material for sodium-ion batteries with intrinsic metallicity, high capacity, and fast ion mobility

The utilization of pristine graphene as an anode material in sodium-ion batteries (SIBs) is limited by its inherent chemical inertness toward Na-ions. To address this issue, we propose a two-dimensional carbon allotrope (named as TD-graphene) by assembling tricyclo[4.4.1.11,6]dodecane (C12H20) skeleton. The topological non-hexagonal feature of C12H20 increases the degree of local carbon-ring disorder and introduces additional electron-deficient regions on the surface, thus enhancing the adsorption capability of Na. TD-graphene demonstrates exceptional stability across the energetic, thermodynamic, dynamic, and mechanical aspects. As a promising anode for SIBs, it exhibits an intrinsic metallicity, an ultra-high storage capacity (1487.58 mA h g−1), a low diffusion barrier (0.20 eV), a low average open-circuit voltage (0.33 V), and a small lattice expansion (0.6%). The presence of solvents with high dielectric constants improves the adsorption and migration capability of Na. Furthermore, taking into account the limitation of single-layer materials in practical applications, we employ h-BN as a promising substrate for TD-graphene, which can boost the Na adsorption and diffusion performance. These results render TD-graphene as a promising high-performance anode material for SIBs.

Boosting Potassium Adsorption and Diffusion Performance of Carbon Anodes for Potassium-Ion Batteries via Topology and Curvature Engineering: From KT-Graphene to KT-CNTs.

We propose a two-dimensional carbon allotrope (named KT-graphene) by incorporating kagome and tetragonal lattices consisting of trigonal, quadrilateral, octagonal, and dodecagonal rings. The introduction of non-hexagonal rings can give rise to the localized electronic states that improve the chemical reactivity toward potassium, making KT-graphene a high-performance anode material for potassium-ion batteries. It shows a high theoretical capacity (892 mAh g-1), a low diffusion barrier (0.33 eV), and a low average open-circuit voltage (0.51 V). The presence of electrolyte solvents is propitious to boost the K-ion adsorption and diffusion capabilities. Moreover, one-dimensional nanotubes (KT-CNTs), rolled up by the KT-graphene sheet, are metallic regardless of the tube diameter. As the curvature increases, KT-CNTs exhibit significantly increased surface activity, which can promote the electron-donating ability of K. Furthermore, the curvature effect greatly enhances the efficiency of K diffusion on the inner surface compared to that on the outer surface.

First-principle prediction of Penta-NiN2 monolayer as electrode materials for Na and K ion batteries

The atomic configurations, structural stability, and electrochemical performances of the pentagonal NiN2 (penta-NiN2) monolayer were investigated as an electrode material via density functional theory (DFT) methods. The results reveal that the penta-NiN2 exhibits intrinsic semiconductor characteristics and dynamic stability. The tiny inherent diffusion energy (<0.10 eV), low average open-circuit voltage (OCV) of 0.05–0.25 V and high storage capacity of 1854.67 mA h g−1 and 618.22 mA h g−1 indicate that the penta-NiN2 is prefer to be an anode material for Na/K. This study demonstrates that the 2D penta-NiN2 is highly suitable as an anode material for Na/K batteries.

Two-dimensional graphene+ as an anode material for calcium-ion batteries with ultra-high capacity: a first-principles study.

Multivalent-ion batteries have garnered significant attention due to their high energy density, low cost, and superior safety. Calcium-ion batteries (CIBs) are regarded as the next-generation energy storage systems for their abundant natural resources and bivalent characteristics. However, the absence of high-performance anode materials poses a significant obstacle to the progress of battery technology. Two-dimensional (2D) Dirac materials have excellent conductivity and abundant active sites, rendering them promising candidates as anode materials. A novel 2D Dirac material known as "graphene+" has been theoretically reported, exhibiting prominent properties including good stability, exceptional ductility, and remarkable electronic conductivity. By using first-principles calculations, we systematically investigate the performance of graphene+ as an anode material for CIBs. Graphene+ exhibits an ultra-high theoretical capacity (1487.7 mA h g-1), a small diffusion barrier (0.21 eV), and a low average open-circuit voltage (0.51 V). Furthermore, we investigate the impact of the electrolyte solvation on the performance of Ca-ion adsorption and migration. Upon contact with electrolyte solvents, graphene+ exhibits strong adsorption strength and rapid migration of Ca-ions on its surface. These results demonstrate the promising potential of graphene+ as a high-performance anode material for CIBs.

A new 3D porous metallic carbon allotrope composed of 5–7 nanoribbons as an anode material for sodium-ion batteries

Motivated by the successful synthesis of three-dimensional (3D) graphene monoliths, tremendous effort has been devoted to the design of 3D porous metallic carbon allotropes with rich topology by assembling various nanoribbons for the anode materials of metal-ion batteries in recent years. Going beyond the allotropes reported so far we propose a new 3D carbon monolith, Hex-C57, by using 5–7 nanoribbons observed in the experiment as the building block. Hex-C57 is found to be dynamically, thermally, and mechanically stable, and electronically metallic. An analysis based on the tight-binding model reveals that the metallicity originates from the pz-orbitals of the sp2-hybridized carbon atoms, forming the conducting channels along the axial direction. With the advantages of intrinsic metallicity, mechanical ductility, and ordered pores, Hex-C57 is a highly promising anode material for sodium-ion batteries (SIBs). Calculations of the electrochemical properties show that Hex-C57 possesses a high reversible gravimetric capacity (334.69 mAhg−1) and volumetric capacity (314.61 mAhcm−3), a small volume change (1.45%), very low diffusion barriers (0.046–0.070 eV), and a low average open-circuit voltage (0.18 V). This work not only expands the 3D porous carbon family with different nanoribbons as the building blocks, but also demonstrates the functionality of unconventional 5–7 carbon rings-assembled materials.

Theoretical prediction of metallic R12-graphene as a promising anode material for potassium-ion batteries with high ion mobility, high capacity, and excellent electrolyte wettability

Although graphene has excellent electrical and mechanical properties, the giant delocalized π-electron system makes it chemically inert. Here, we propose an idea to design two-dimensional (2D) carbon allotropes via incorporating multiple rings in sp2-hybridized carbon networks, which can break the π-bonding network and enhance the surface reactivity. By assembling molecule of cyclobut(a)acenaphthylene, we predict a monolayer 2D carbon material, named as R12-graphene, which is composed of quadrilateral, pentagonal, hexagonal, and dodecagonal carbon rings. It shows great stability in energetic, dynamic, thermodynamic, and mechanical aspects. It exhibits high-performance as an anode material for potassium-ion batteries (PIBs), including an intrinsic metallic behavior, a high theoretical capacity (632 mA h g−1), a low K diffusion barrier (0.33 eV), and a low average open-circuit voltage (0.5 V). The presence of electrolytes can provide better K ion adsorption and diffusion capability compared to that in vacuum. Furthermore, R12-graphene has excellent wettability toward some commonly used electrolytes, which is beneficial for improving the charge/discharge rate for PIBs.

Monolayer TiSiP as a high-performance anode for Na-ion batteries

Exploring anode materials with overall excellent performance remains a great challenge for rechargeable Na-ion battery technologies. Herein, we have identified that monolayer TiSiP is just such a prospective anode candidate via first-principles calculations. It is showed to be dynamically, thermally, mechanically, and energetically stable, which provides feasibility for experimental realization. The Na diffusion on the its surface is proved to be ultrafast, with a migration energy barrier as low as 73 meV. Electronic structure confirms that the pristine system undergoes a transition from the semiconductor to metal during the whole sodiation process, which is a significant advantage to the electrode conductivity. More excitingly, monolayer TiSiP can accommodate up to double-sided five-layer adatoms, resulting in an ultrahigh theoretical capacity of 1176 mA h g−1 and a low average open-circuit voltage of 0.195 V. Moreover, the maximally sodiated electrode monolayer yields rather small in-plane lattice expansion of only 1.40%, which ensures reversible deformation and excellent cycling stability as further corroborated by structural relaxation and ab initio molecular dynamics simulation. Overall, all of these results point to the potential that monolayer TiSiP can serve as a promising anode candidate for application in high-performance low-cost Na-ion batteries.

PtS2/WSe2 heterostructure for thermoelectric and Li-ion battery Applications: A First-Principles study

Van der Waals’ two-dimensional heterostructure engineering offers great potential in applications of electronic devices, battery applications, thermoelectric. Encouraged by the successful synthesis of PtS2/WSe2 heterostructure, we explore its potential in thermoelectric and Li-ion battery applications by first-principles calculations. Due to these multi-valley degenerate valence and conduction bands, a large power factor of 0.007 W/mK2 is attained. Due to the significant interface effect, PtS2/WSe2 heterostructure can strongly adsorb Li atoms with −2.69 eV adsorption strength on the middle of PtS2/WSe2 heterostructure layers. Also, an extremely fast Li diffusion rate was found in this heterostructure (as low as 20 meV), which is close to the recently reported MXene. Large theoretical volumetric storage capacity of 1283.98 mA h/cm3, in the meanwhile a rather low average Open-circuit voltage (0.07 V) also purports that PtS2/WSe2 heterostructure is a quite promising anode material in Li-ion batteries with high power densities and fast charge/discharge rates.

Aluminene as a Low-Cost Anode Material for Li- and Na-Ion Batteries.

Two-dimensional (2D) materials are promising candidates for next-generation battery technologies owing to their high surface area, excellent electrical conductivity, and lower diffusion energy barriers. In this work, we use first-principles density functional theory to explore the potential for using a 2D honeycomb lattice of aluminum, referred to as aluminene, as an anode material for metal-ion batteries. The metallic monolayer shows strong adsorption for a range of metal atoms, i.e., Li, Na, K, and Ca. We observe surface diffusion barriers as low as 0.03 eV, which correlate with the size of the adatom. The relatively low average open-circuit voltages of 0.27 V for Li and 0.42 V for Na are beneficial to the overall voltage of the cell. The estimated theoretical specific capacity has been found to be 994 mA h/g for Li and 870 mA h/g for Na. Our research highlights the promise of aluminene sheets in the development of low-cost, high-capacity, and lightweight advanced rechargeable ion batteries.

Density Functional Theory Study of Bilayer Borophene-Based Anode Material for Rechargeable Lithium Ion Batteries.

The bilayer borophene has been successfully fabricated in experiments recently and possesses superior antioxidation and robust metallic properties, which holds great promise for the future anode materials of Li-ion batteries. Herein, using first-principles calculations, two bilayer borophenes including P6/mmm or P6̅m2 symmetry groups with or without vacancy defects are comprehensively explored and acted as electrode materials with high performance in Li-ion batteries. The charge density difference, adsorption energies, and Bader charge analysis are calculated and discussed for single lithium adsorbed on bilayer borophene. The results shown that with the increase of lithium concentration, the adsorption energies are rapidly decreased due to the repulsion of boron atoms except for the P6̅m2 systems with double side adsorption and corresponding energies remain the narrow range. Meanwhile, the partial density of states shows metallic character after lithium adsorption and indicates good conductivity for the charge-discharge process. Furthermore, small diffusion barriers, low average open-circuit voltage, can be achieved, and large storage capacity is up to 930.2 mA h/g at the lower lithium content of 0.375. These results propose that bilayer borophene might be a good choice for anode material applications in future Li-ion batteries with fast ion diffusion and high power density.

Theoretical prediction of Be2B monolayer as an ultra-high performance anode material for magnesium-ion batteries

Magnesium-ion batteries (MIBs) are expected to be an alternative to lithium-ion batteries due to the lower cost and immanent safety of Mg. Presently, the major difficulty in breaking through MIBs technology is the lack of desirable anode materials. Based on first-principles calculations, we predict a two-dimensional material named the Be2B monolayer as an excellent anode material. The structural stability is confirmed by superior cohesive energy, positive phonon modes, excellent thermal stability, and strong mechanical stability. Afterward, we explore the performance of the Be2B monolayer as the anode material for MIBs. It exhibits stable Mg atom adsorption with an energy of −0.7 eV, low diffusion barrier (0.1 eV), ultra-high specific capacity (7436 mA h g−1), tiny lattice expansion (0.3%), and low average open-circuit voltage (0.29 V). Thereby, the above-mentioned intriguing findings suggest that the Be2B monolayer can act as a promising anode material for high performance MIBs.

Theoretical investigation of the V2BX2 (X = S, Se, and Te) monolayers as anode materials for Na-ion batteries

The structural, electronic, and electrochemical properties of chalcogen-functionalized V2BX2 (X = S, Se, and Te) monolayers as anode materials for Na-ion batteries (NIBs) were systematically investigated using the first-principles method. It is found that the V2BX2 monolayers exhibit good dynamical stability, thermal stability, and electronic conductivity. Furthermore, the small diffusion barriers (about 0.1 eV) display the fast charge/discharge rate, the low average open-circuit voltages (OCVs) (0.282–0.163 V) are favorable for high-voltage NIBs, and the small lattice changes (less than 5 %) demonstrate good cycling performance. Especially, the V2BS2 and V2BSe2 have high specific capacities of 605.67 and 395.59 mA h g−1 for NIBs, respectively. All of these excellent properties suggest that V2BX2 monolayers could be promising anode materials for NIBs.

Metallic 1H-BeP2 monolayer as a potential anode material for Li-ion/Na-ion batteries: A first principles study

The selection of a suitable two-dimensional anode material is a fundamental step in developing the batteries to gain excellent performance. Herein, based on the comprehensive first-principles computations, we systematically explored the possibility of two-dimensional 1 H-BeP2 monolayer as the anode material of lithium/sodium-ion (Li/Na-ion) batteries. Our results show that 1 H-BeP2 monolayer possesses metal characteristics, which provides good conductivity and can effectively guarantee fast electronic transmission. Meanwhile, the 1 H-BeP2 monolayer possesses thermal and dynamic stabilities. In addition, it is worth noting that 1 H-BeP2 monolayer also has other excellent performance required for metal-ion batteries anode, not only a high theoretical storage capacity of 755 mAh/g, but also an ultra-low diffusion barrier (Li/Na: 0.198/0.095 eV) and low average open-circuit voltage (Li/Na: 0.69/0.36 eV). Furthermore, it also possesses a relatively small lattice changes (Li/Na: 4.8/3.4%) during the charge and discharge process. Finally, the metallic behavior of the 1 H-BeP2 monolayer is maintained throughout with different adsorption concentrations of Li/Na ions, which is an excellent feature for the battery application. All these appealing results demonstrate that 1 H-BeP2 monolayer is a promising flexible anode of Li/Na-ion batteries.

Novel ternary compound transition metal dichalcogenide TiNbS4 as promising anodes materials for Li-ion batteries: A DFT study

Searching for suitable anodes with good performance is a key challenge in the development of rechargeable Li-ion batteries (LIBs). In this paper, the performance of a new two-dimensional transition metal dichalcogenide (TMDs) material TiNbS4 as anode material is systematically studied by density functional theory (DFT). Firstly, the stability of the crystal structure is verified by calculating the phonon spectra, it is also demonstrated that TiNbS4 has good electronic conductivity based on the energy band and electronic density of states, which is important for the anode material of LIBs. Secondly, the adsorption and diffusion behavior of Li on the surface of TiNbS4 is studied, and the theoretical capacity and open-circuit voltage are calculated. It exhibits a high theoretical capacity (990 mA·hg−1) that are much better than the graphite (372 mA·hg−1), and a low average open-circuit voltage (0.63 V). Combining those advanced performance, TiNbS4 monolayer sheets can be used as an ideal anode material.

Metallic CrP2 monolayer: potential applications in energy storage and conversion.

Phosphorus-rich compounds have emerged as a promising class of energy storage and conversion materials due to their interesting structures and electrochemical properties. Herein, we propose that a metallic CrP2 monolayer, isomorphic to 1H-phase MoS2, is a good prospect as an anode for K-ion batteries and a catalyst for hydrogen evolution through first-principles calculations. The CrP2 monolayer demonstrates not only a desirable high K storage capacity (940 mA h g-1) but also a low K-ion diffusion barrier (0.10 eV) and average open circuit voltage (0.40 V). On the other hand, its Gibbs free energy (0.02 eV)/active site density is superior/comparable to that of commercial Pt, resulting from the contribution of the lone pair electrons of the P atom. Its high structural stability and intrinsic metallicity can ensure high safety and performance during the cyclic process. These interesting properties make the CrP2 monolayer a promising multifunctional material for energy storage and conversion devices.

Monolayer α-beryllene as an anode material for magnesium ion batteries with high capacity and low diffusion energy barrier.

High specific capacity and fast charge/discharge rate are important indicators for the development of next-generation ion batteries. Compared with conventional monovalent ion batteries like lithium-ion batteries and sodium-ion batteries, multivalent ion batteries have attracted extensive attention owing to their high energy densities. Here, we systematically explore the interactions between Mg atoms and α-beryllene monolayers by means of density functional theory calculations. Mg atoms can be adsorbed stably on α-beryllene monolayers with the adsorption energy of -0.24 eV. The low diffusion energy barriers (0.099/0.101 eV) indicate the rapid mobility of Mg during the charge/discharge process. Moreover, the α-beryllene monolayer exhibits an ultra-high theoretical specific capacity of 5956 mA h g-1 for Mg, a low average open-circuit voltage of 0.24 V, and a tiny volume change of -1.08%. Finally, the constructed h-BN/α-beryllene heterostructure shows that h-BN can serve as a protective cover to preserve pristine α-beryllene in respect of metallicity, Mg adsorption capability, and fast ionic mobility. The above mentioned outstanding results make α-beryllene a promising anode material for magnesium-ion batteries.

Layer-stacking of chalcogenide-terminated MXenes Ti2CT2(T = O, S, Se, Te) and their applications in metal-ion batteries

Owning to limited supply of lithium for Li-ion batteries, the development of non-Li-ion batteries (such as Na+, K+ Mg2+, Ca2+, and Al3+ ion batteries) has attracted significant research interest. In this work, by means of the first-principles calculations, we systematically investigated the performance of chalcogenide-terminated MXenes Ti2CT2 (T = O, S, Se, and Te) as electrodes for Li-ion and non-Li-ion batteries, as well as the layer-stacking and electronic properties of Ti2CT2. We find that the stacking type of O and Te terminated Ti2C multilayers with AA stacking differs from that of S and Se terminated Ti2C multilayers with AB stacking. More importantly, Ti2CO2 monolayer can be potential anode material for Na- and K-ion batteries with high capacities and very low diffusion barriers (0.03–0.11 eV), while Ti2CS2 and Ti2CSe2 are promising anode materials with relatively low average open circuit voltages (OCVs) for Na-, K-, and Ca-ion batteries (0.4–0.87 V). Among these materials, Ti2CS2 exhibits the largest ion capacity of 616 mAh g−1. These results of our work may inspire further studies of Ti2C-MXenes multilayers as electrodes for metal-ion batteries either experimentally or theoretically.

Boron-doped g-CN monolayer as a promising anode for Na/K-ion batteries

Graphitic carbon nitride (CxNy) has a two-dimensional structure similar to N-doped graphene, which is nitrogen-rich and contains porous defect sites that can serve as atomic storage sites for alkali metals. Compared with C3N4, the most widely reported carbon nitride family, g-CN is structurally stable without graphitic nitrogen. However, the adsorption energy of Li/Na/K in the pore size is too negative (-2.60/-2.99/-3.11 eV) to be desorbed, and the high diffusion barrier of Li/Na/K ion (2.94/3.11/2.43 eV) implies the low charge/discharge rate for metal-ion batteries. Here, we showed that doping B atoms into the pore sites of g-CN (BC3N3) possess some advantages for application in batteries. Specifically, the BC3N3 monolayer has excellent stability, with moderate adsorption ability for Na/K (-0.54/-0.98 eV) and a much lower diffusion barrier of ion (0.73/0.35 eV). BC3N3 shows excellent theoretical specific capacity (603.30/904.95 mAh/g) and low average open-circuit voltage as an anode material for Na/K-ion batteries. Moreover, under a small amount of alkali metal adsorption, BC3N3 exhibits metallic properties and the electrical conductivity of BC3N3 is improved. These favorable properties indicate that the B-doped g-CN monolayer is a promising anode material for Na/K ion batteries and this approach can be extended to other porous carbon-nitrogen structures.

PHP-graphene nanoribbon-assembled porous metallic carbon for sodium-ion battery anode with high specific capacity

In recent years, a number of three-dimensional (3D) porous metallic carbon allotropes have been proposed to be used as anode materials for metal-ion batteries by assembling graphene or penta-graphene nanoribbons. Here, based on density functional theory and tight-binding model, we design a new 3D porous metallic carbon monolith (termed Hex-C568) consisting of PHP-graphene nanoribbons which contain pentagonal, hexagonal and octagonal rings. It is thermally, dynamically and mechanically stable. We find that its metallicity is attributed to the delocalized electrons in the p-orbitals of the sp2 hybridized carbon atoms, and Hex-C568 is a promising anode material for Na-ion batteries with high performance. Its reversible gravimetric and volumetric capacities are 787.53 mAhg−1 and 718.10 mAhcm−3, respectively, with low diffusion energy barrier (0.04–0.30 eV), low average open-circuit voltage (0.26 V), and small volume change during the charging/discharging process (3.71%). These electrochemical properties are superior to those of most recently reported anode materials, suggesting that PHP-graphene nanoribbon is a promising building unit for the design of novel carbon anode materials going beyond graphene and penta-graphene.