Fluorinated Fullerenes as Electrolyte Additives for High Ionic Conductivity Lithium-Ion Batteries.

Currently, lithium-ion batteries have an increasingly urgent need for high-performance electrolytes, and additives are highly valued for their convenience and cost-effectiveness features. In this work, the feasibilities of fullerenes and fluorinated fullerenes as typical bis(fluorosulfonyl)imide/1,2-dimethoxymethane (LiFSI/DME) electrolyte additives are rationally evaluated based on density functional theory calculations and molecular dynamic simulations. Interestingly, electronic structures of C60, C60F2, C60F4, C60F6, 1-C60F8, and 2-C60F8 are found to be compatible with the properties required as additives. It is noted that that different numbers and positions of F atoms lead to changes in the deformation and electronic properties of fullerenes. The F atoms not only show strong covalent interactions with C cages, but also affect the C-C covalent interaction in C cages. In addition, molecular dynamic simulations unravel that the addition of trace amounts of C60F4, C60F6, and 2-C60F8 can effectively enhance the Li+ mobility in LiFSI/DME electrolytes. The results expand the range of applications for fullerenes and their derivatives and shed light on the research into novel additives for high-performance electrolytes.

Unraveling the Emerging Photocatalytic, Thermoelectric, and Topological Properties of Intercalated Architecture MZX (M = Ga and In; Z = Si, Ge and Sn; X = S, Se, and Te) Monolayers.

The continuous advancements in studying two-dimensional (2D) materials pave the way for groundbreaking innovations across various industries. In this study, by employing density functional theory calculations, we comprehensively elucidate the electronic structures of MZX (M = Ga and In; Z = Si, Ge, and Sn; X = S, Se, and Te) monolayers for their applications in photocatalytic, thermoelectric, and spintronic fields. Interestingly, GaSiS, GaSiSe, InSiS, and InSiSe monolayers are identified to be efficient photocatalysts for overall water splitting with band gaps close to 2.0 eV, suitable band edge positions, and excellent optical harvest ability. In addition, the InSiTe monolayer exhibits a ZT value of 1.87 at 700 K, making it highly appealing for applications in thermoelectric devices. It is further highlighted that GaSnTe, InSnS, and InSnSe monolayers are predicted to be 2D topological insulators (TIs) with bulk band gaps of 115, 54, and 152 meV, respectively. Current research expands the family of 2D GaGeTe materials and establishes a path toward the practical utilization of MZX monolayers in energy conversion and spintronic devices.

Computational mining of GeH-based Janus III-VI van der Waals heterostructures for solar cell applications.

The asymmetrical group III-VI monolayer Janus M2XY (M = Al, Ga, In; X ≠ Y = S, Se, Te) have attracted widespread attention due to their significant optical absorption properties, which are the potential building blocks for van der Waals (vdW) heterostructure solar cells. In this study, we unraveled an In2STe/GeH vdW heterostructure as a candidate for solar cells by screening the Janus M2XY and GeH monolayers on lattice mismatches and electronic band structures based on first-principles calculations. The results highlight that the In2STe/GeH vdW heterostructure exhibits a type-II band gap of 1.25 eV. The optical absorption curve of the In2STe/GeH vdW heterostructure indicates that it possesses significant optical absorption properties in the visible and ultraviolet light areas. In addition, we demonstrate that the In2STe/GeH vdW heterostructure shows high and directionally anisotropic carrier mobility and good stability. Furthermore, strain engineering improves the theoretical power conversion efficiency of the In2STe/GeH vdW heterostructure up to 19.71%. Our present study will provide an idea for designing Janus M2XY and GeH monolayer-based vdW heterostructures for solar cell applications.

Promising M2CO2/MoX2 (M = Hf, Zr; X = S, Se, Te) Heterostructures for Multifunctional Solar Energy Applications.

Two-dimensional van der Waals (vdW) heterostructures are potential candidates for clean energy conversion materials to address the global energy crisis and environmental issues. In this work, we have comprehensively studied the geometrical, electronic, and optical properties of M2CO2/MoX2 (M = Hf, Zr; X = S, Se, Te) vdW heterostructures, as well as their applications in the fields of photocatalytic and photovoltaic using density functional theory calculations. The lattice dynamic and thermal stabilities of designed M2CO2/MoX2 heterostructures are confirmed. Interestingly, all the M2CO2/MoX2 heterostructures exhibit intrinsic type-II band structure features, which effectively inhibit the electron-hole pair recombination and enhance the photocatalytic performance. Furthermore, the internal built-in electric field and high anisotropic carrier mobility can separate the photo-generated carriers efficiently. It is noted that M2CO2/MoX2 heterostructures exhibit suitable band gaps in comparison to the M2CO2 and MoX2 monolayers, which enhance the optical-harvesting abilities in the visible and ultraviolet light zones. Zr2CO2/MoSe2 and Hf2CO2/MoSe2 heterostructures possess suitable band edge positions to provide the competent driving force for water splitting as photocatalysts. In addition, Hf2CO2/MoS2 and Zr2CO2/MoS2 heterostructures deliver a power conversion efficiency of 19.75% and 17.13% for solar cell applications, respectively. These results pave the way for exploring efficient MXenes/TMDCs vdW heterostructures as photocatalytic and photovoltaic materials.

Comprehensive understanding of intrinsic mobility and sub-10 nm quantum transportation in Ga2SSe monolayer.

Two-dimensional chalcogenides could play an important role in solving the short channel effect and extending Moore's law in the post-Moore era due to their excellent performances in the spintronics and optoelectronics fields. In this paper, based on theoretical calculations combining density functional theory and non-equilibrium Green's function, we have systematically explored the intrinsic mobility in the Ga2SSe monolayer and quantum transport properties of sub-10 nm Ga2SSe field-effect transistors (FET). Interestingly, the Ga2SSe monolayer presents high intrinsic electron mobility up to 104 cm2 (V s)-1. It is highlighted that the intrinsic mobility in the Ga2SSe monolayer is significantly restrained by phonon scattering, where the out-of-plane acoustic mode and high-frequency optic phonon mode are found predominantly coupled with the electrons. As a result, the n-type doping sub-10 nm Ga2SSe FETs represent distinguished transport properties. In particular, even the gate length is shortened to 3 nm, the on-state current, delay time and power consumption of the n-type doping Ga2SSe FET along the armchair direction can reach the International Technology Roadmap for Semiconductor industry standards for high-performance requirements. Our present study paves the way for the application of Ga2SSe monolayers in ultra-small sized FETs in the post-silicon era.

Computational discovery of PtS2/GaSe van der Waals heterostructure for solar energy applications.

2D van der Waals (vdW) heterostructures as potential materials for solar energy-related applications have been brought to the forefront for researchers. Here, by employing first-principles calculations, we proposed that the PtS2/GaSe vdW heterostructure is a distinguished candidate for photocatalytic water splitting and solar cells. It is shown that the PtS2/GaSe heterostructure exhibits high thermal stability with an indirect band gap of 1.81 eV. We further highlighted the strain induced type-V to type-II band alignment transitions and band gap variations in PtS2/GaSe heterostructures. More importantly, the outstanding absorption coefficients in the visible light region and high carrier mobility further guarantee the photo energy conversion efficiency of PtS2/GaSe heterostructures. Interestingly, the natural type-V band alignments of PtS2/GaSe heterostructures are appropriate for the redox potential of water. On the other hand, the power conversion efficiency of ZnO/(PtS2/GaSe heterostructure)/CIGS (copper indium gallium diselenide) solar cells can achieve ∼17.4%, which can be further optimized up to ∼18.5% by increasing the CIGS thickness. Our present study paves the way for facilitating the potential application of vdW heterostructures as a promising photocatalyst for water splitting as well as the buffer layer for solar cells.

High-performance III-VI monolayer transistors for flexible devices.

Group III-VI family MX (M = Ga and In, and X = S, Se, and Te) monolayers have attracted global interest for their potential applications in electronic devices due to their unexpectedly high carrier mobility. Herein, via density functional theory calculations as well as ab initio quantum transport simulations, we investigated the performance limits of MX monolayer metal oxide semiconductor field-effect transistors (MOSFETs) at the sub-10 nm scale. Our results highlighted that the MX monolayers possessed good structural stability and mechanical isotropy with large ultimate strains and low Young's modulus, which are intensely anticipated in the next-generation flexible devices. More importantly, the MX monolayer MOSFETs show excellent device performance under optimal schemes. The on-state current, delay time, and power dissipation of the MX monolayer MOSFETs satisfy the International Technology Roadmap for Semiconductors (ITRS) 2013 requirements for high-performance devices. Interestingly, the sub-threshold swings were in a very low range from 68 mV dec-1 to 108 mV dec-1, which indicated the favorable gate control ability for fast switching. Therefore, we believe that our findings shed light on the design and application of MX monolayer-based MOSFETs in next-generation flexible electronic devices.

Comprehensive understanding of intrinsic mobility in the monolayers of III-VI group 2D materials.

Monolayers of III-VI group two-dimensional (2D) materials MX (M = Ga and In and X = S, Se, and Te) have attracted global interest for potential applications in electronic and photoelectric devices due to their attractive physical and chemical characteristics. However, a comprehensive understanding of the distinguished carrier mobility in MX monolayers is of great importance and not yet clear. Herein, using a Boltzmann transport equation (BTE) solver and first principles calculations, we have precisely revealed that the intrinsic mobility in MX monolayers is significantly limited by phonon scattering. Note that the longitudinal acoustic phonon mode and optic phonon modes and were found predominantly coupled with electrons, which strongly restrained the intrinsic mobility in the MX monolayers. Interestingly, apart from a moderate band gap, the GaSe and GaTe monolayers exhibit high electron mobility exceeding 103 cm2 V-1 s-1 and may serve as outstanding electron transport channels. We believe that our findings will shed light on the design and applications of MX monolayers and 2D materials in nanoscale electronic and photoelectric devices.

The electronic origin of shear-induced direct to indirect gap transition and anisotropy diminution in phosphorene.

Artificial monolayer black phosphorus, so-called phosphorene, has attracted global interest with its distinguished anisotropic, optoelectronic, and electronic properties. Here, we unraveled the shear-induced direct-to-indirect gap transition and anisotropy diminution in phosphorene based on first-principles calculations. Lattice dynamic analysis demonstrates that phosphorene can sustain up to 10% applied shear strain. The bandgap of phosphorene experiences a direct-to- indirect transition when 5% shear strain is applied. The electronic origin of the direct-to-indirect gap transition from 1.54 eV at ambient conditions to 1.22 eV at 10% shear strain for phosphorene is explored. In addition, the anisotropy diminution in phosphorene is discussed by calculating the maximum sound velocities, effective mass, and decomposed charge density, which signals the undesired shear-induced direct-to-indirect gap transition in applications of phosphorene for electronics and optoelectronics. On the other hand, the shear-induced electronic anisotropy properties suggest that phosphorene can be applied as the switcher in nanoelectronic applications.

Magnetic-ferroelectric synergic control of multilevel conducting states in van der Waals multiferroic tunnel junctions towards in-memory computing.

van der Waals (vdW) multiferroic tunnel junctions (MFTJs) based on two-dimensional materials have gained significant interest due to their potential applications in next-generation data storage and in-memory computing devices. In this study, we construct vdW MFTJs by employing monolayer Mn2Se3 as the spin-filter tunnel barrier, TiTe2 as the electrodes and In2S3 as the tunnel barrier to investigate the spin transport properties based on first-principles quantum transport calculations. It is highlighted that apparent tunneling magnetoresistance (TMR) and tunneling electroresistance (TER) effects with a maximum TMR ratio of 6237% and TER ratio of 1771% can be realized by using bilayer In2S3 as the tunnel barrier under finite bias. Furthermore, the physical origin of the distinguished TMR and TER effects is unraveled from the k||-resolved transmission spectra and spin-dependent projected local density of states analysis. Interestingly, four distinguishable conductance states reveal the implementation of four-state nonvolatile data storage using one MFTJ unit. More importantly, in-memory logic computing and multilevel data storage can be achieved at the same time by magnetic switching and electrical control, respectively. These results shed light on vdW MFTJs in the applications of in-memory computing as well as multilevel data storage devices.

Contact engineering for 2D Janus MoSSe/metal junctions.

The flourish of two-dimensional (2D) materials provides a versatile platform for building high-performance electronic devices in the atomic thickness regime. However, the presence of the high Schottky barrier at the interface between the metal electrode and the 2D semiconductors, which dominates the injection and transport efficiency of carriers, always limits their practical applications. Herein, we show that the Schottky barrier can be controllably lifted in the heterostructure consisting of Janus MoSSe and 2D vdW metals by different means. Based on density functional theory calculations and machine learning modelings, we studied the electrical contact between semiconducting monolayer MoSSe and various metallic 2D materials, where a crossover from Schottky to Ohmic/quasi-Ohmic contact is realized. We demonstrated that the band alignment at the interface of the investigated metal-semiconductor junctions (MSJs) deviates from the ideal Schottky-Mott limit because of the Fermi-level pinning effects induced by the interface dipoles. Besides, the effect of the thickness and applied biaxial strain of MoSSe on the electronic structure of the junctions are explored and found to be powerful tuning knobs for electrical contact engineering. It is highlighted that using the sure-independence-screening-and-sparsifying-operator machine learning method, a general descriptor WM3/exp(Dint) was developed, which enables the prediction of the Schottky barrier height for different MoSSe-based MSJ. These results provide valuable theoretical guidance for realizing ideal Ohmic contacts in electronic devices based on the Janus MoSSe semiconductors.

Predicted superconductivity in one-dimensional A3Hf2B3-type electrides.

Inorganic electrides are considered potential superconductors due to the unique properties of their anionic electrons. However, most electrides require external high-pressure conditions to exhibit considerable superconducting transition temperatures (Tc). Therefore, searching for superconducting electrides under low or moderate external pressures is of significant research interest and importance. In this work, a series of A3Hf2B3-type compounds (A = Mg, Ca, Sr, Ba; B = Si, Ge, Sn, Pb) were constructed and systematically studied based on density functional theory calculations. According to the analysis of the electronic structures and phonon dispersion spectrums, stable one-dimensional electrides Ca3Hf2Ge3, Ca3Hf2Sn3, and Sr3Hf2Pb3, were screened out. Interestingly, the superconductivity of these electrides were predicted from electron phonon coupling calculations. It is highlighted that Sr3Hf2Pb3 showed the highest Tc, reaching 4.02 K, while the Tc values of Ca3Hf2Ge3 and Ca3Hf2Sn3 were 1.16 K and 1.04 K, respectively. Moreover, the Tc value of Ca3Hf2Ge3 can be increased to 1.96 K under 20 GPa due to the effect of phonon softening. This work enriches the types of superconducting electrides and has important guiding significance for the research on constructing electrides and related superconducting materials.

Enhanced Electrochemical Performance of a Ti-Cr-Doped LiMn1.5Ni0.5O4 Cathode Material for Lithium-Ion Batteries.

Ti, Cr dual-element-doped LiMn1.5Ni0.5O4 (LNMO) cathode materials (LTNMCO) were synthesized by a simple high-temperature solid-phase method. The obtained LTNMCO shows the standard structure of the Fd3®m space group, and the Ti and Cr doped ions may replace the Ni and Mn sites in LNMO, respectively. The effect of Ti-Cr doping and single-element doping on the structure of LNMO was studied by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) characteristics. The LTNMCO exhibited excellent electrochemical properties with a specific capacity of 135.1 mAh·g-1 for the first discharge cycle and a capacity retention rate of 88.47% at 1C after 300 cycles. The LTNMCO also has high rate performance with a discharge capacity of 125.4 mAh·g-1 at a 10C rate, 93.55% of that at 0.1C. In addition, the CIV and EIS results show that the LTNMCO showed the lowest charge transfer resistance and the highest diffusion coefficient of lithium ions. The enhanced electrochemical properties may be due to a more stable structure and an optimized Mn3+ content in LTNMCO through TiCr doping.

Out-of-plane polarization modulated band alignments inß-In2X3/α-In2X3(X = S and Se) vdW heterostructures.

The construction of two-dimensional (2D) van der Waals (vdW) heterostructures is an effective strategy to overcome the intrinsic disadvantages of individual 2D materials. Herein, by employing first-principles calculations, the electronic structures and potential applications in the photovoltaic field of theß-In2X3/α-In2X3(X = S and Se) vdW heterostructures have been systematically unraveled. Interestingly, the band alignments ofß-In2S3/α-In2S3,ß-In2Se3/α-In2Se3, andß-In2Se3/α-In2S3heterostructures can be transformed from type-I to type-II by switching the polarization direction ofα-In2X3layers. It is highlighted that the light-harvesting ability of theß-In2X3/α-In2X3vdW heterostructures is significantly higher than the corresponding monolayers in nearly the entire visible light region. Interestingly, type-IIß-In2S3/α-In2Se3↓ heterostructure can achieve the power conversion efficiency of 17.9%, where theα-In2Se3layer acts as a donor and theß-In2S3layer displays as the acceptor. The present research not only provides an in-depth understanding that the out-of-plane polarization ofα-In2X3monolayers can efficiently modulate the band edge alignment of theß-In2X3/α-In2X3vdW heterostructures, but also paves the way for the application of these heterostructures in the field of photovoltaics and optoelectronics.

Enhancement of the thermoelectric properties of Zintl phase SrMg2Bi2 by Na-doping.

Due to their low lattice thermal conductivity and manipulable electronic properties, AB2X2 Zintl phases have been widely studied for thermoelectric applications. This has motivated numerous efforts to focus on the exploration of novel AB2X2 Zintl thermoelectrics. In this study, SrMg2Bi2 was systematically investigated to reveal its potential for thermoelectric application. Pristine SrMg2Bi2 exhibits an intrinsic p-type semiconducting behavior. The Hall carrier concentration (nH) was efficiently increased to ∼9 × 1019 cm-3 by Na-substitution at the Sr site. The increased nH leads to enhanced electrical conductivity, but reduced Seebeck coefficient. Moreover, Na doping effectively decreased the thermal conductivity because of the intensified scattering from defects and lattice distortion. Thus, the zT of the Na-doped SrMg2Bi2 can reach 0.44 and be extremely higher than that of the pristine one. The well-known single parabolic band (SPB) model estimated that the increase in Nv and m* through doping boosts the electrical conductivity. This work sheds light on the discovery of new prospective thermoelectric materials and demonstrates that Bi-based p-type AB2X2 Zintl phases can achieve high thermoelectric performance.

Strain-Enhanced Thermoelectric Performance in GeS2 Monolayer.

Strain engineering has attracted extensive attention as a valid method to tune the physical and chemical properties of two-dimensional (2D) materials. Here, based on first-principles calculations and by solving the semi-classical Boltzmann transport equation, we reveal that the tensile strain can efficiently enhance the thermoelectric properties of the GeS2 monolayer. It is highlighted that the GeS2 monolayer has a suitable band gap of 1.50 eV to overcome the bipolar conduction effects in materials and can even maintain high stability under a 6% tensile strain. Interestingly, the band degeneracy in the GeS2 monolayer can be effectually regulated through strain, thus improving the power factor. Moreover, the lattice thermal conductivity can be reduced from 3.89 to 0.48 W/mK at room temperature under 6% strain. More importantly, the optimal ZT value for the GeS2 monolayer under 6% strain can reach 0.74 at room temperature and 0.92 at 700 K, which is twice its strain-free form. Our findings provide an exciting insight into regulating the thermoelectric performance of the GeS2 monolayer by strain engineering.

Giant tunneling magnetoresistance in two-dimensional magnetic tunnel junctions based on double transition metal MXene ScCr2C2F2.

Two-dimensional (2D) transition metal carbides (MXenes) with intrinsic magnetism and half-metallic features show great promising applications for spintronic and magnetic devices, for instance, achieving perfect spin-filtering in van der Waals (vdW) magnetic tunnel junctions (MTJs). Herein, combining density functional theory calculations and nonequilibrium Green's function simulations, we systematically investigated the spin-dependent transport properties of 2D double transition metal MXene ScCr2C2F2-based vdW MTJs, where ScCr2C2F2 acts as the spin-filter tunnel barriers, 1T-MoS2 acts as the electrode and 2H-MoS2 as the tunnel barrier. We found that the spin-up electrons in the parallel configuration state play a decisive role in the transmission behavior. We found that all the constructed MTJs could hold large tunnel magnetoresistance (TMR) ratios over 9 × 105%. Especially, the maximum giant TMR ratio of 6.95 × 106% can be found in the vdW MTJ with trilayer 2H-MoS2 as the tunnel barrier. These results indicate the potential for spintronic applications of vdW MTJs based on 2D double transition metal MXene ScCr2C2F2.

Influence of Al-O and Al-C Clusters on Defects in Graphene Nanosheets Derived from Coal-Tar Pitch via Al4C3 Precursor.

By treating Al4C3 as the precursor and growth environment, graphene nanosheets (GNs) can efficiently be derived from coal-tar pitch, which has the advantages of simple preparation process, high product quality, green environmental protection, low equipment requirements and low preparation cost. However, the defects in the prepared GNs have not been well understood. In order to optimize the preparation process, based on density functional theory calculations, the influence mechanism of Al-O and Al-C clusters on defects in GNs derived from coal-tar pitch via Al4C3 precursor has been systematically investigated. With minute quantities of oxygen-containing defects, Al-O and Al-C clusters have been realized in the prepared GNs from X-ray photoelectron spectroscopy analysis. Therefore, the influences of Al-O and Al-C clusters on graphene with vacancy defects and oxygen-containing defects are systematically explored from theoretical energy, electron localization function and charge transfer analysis. It is noted that the remaining Al-O and Al-C clusters in GNs are inevitably from the thermodynamics point of view. On the other hand, the existence of defects is beneficial for the further adsorption of Al-O and Al-C clusters in GNs.

Computational mining of endohedral C70 electrides: tri-metal alkali and alkaline-earth encapsulation.

C70 is the second most abundant fullerene next to C60. In this work, the exploration of C70 based electrides is proposed by theoretical encapsulation of group I/II trimetallic clusters into the C70 cage. Herein, we provide computational evidence that endohedral metallofullerenes M3@C70 (M = Li, Na, K, Be, Mg, Ca, Sr, Ba) can exist stably by calculating encapsulation energies and analyzing atom centered density matrix propagation molecular dynamics simulations. According to the results of the atoms in molecules analysis, electron localization functions and nonlinear optical properties, M3@C70 (M = Li, Be, Mg, Ca) fullerenes are identified as electrides. Interestingly, Li3@C70 and Be3@C70 are the systems with better electride performances among alkali metal and alkaline earth metal systems, respectively. It is worth noting that C70 can improve the polarizability and first hyperpolarizability of electrides compared with C60. Our work unearths the potential of M3@C70 electride systems and paves the way for the research of C70-based electrides.

InSe/Te van der Waals Heterostructure as a High-Efficiency Solar Cell from Computational Screening.

Designing the electronic structures of the van der Waals (vdW) heterostructures to obtain high-efficiency solar cells showed a fascinating prospect. In this work, we screened the potential of vdW heterostructures for solar cell application by combining the group III-VI MXA (M = Al, Ga, In and XA = S, Se, Te) and elementary group VI XB (XB = Se, Te) monolayers based on first-principle calculations. The results highlight that InSe/Te vdW heterostructure presents type-II electronic band structure feature with a band gap of 0.88 eV, where tellurene and InSe monolayer are as absorber and window layer, respectively. Interestingly, tellurene has a 1.14 eV direct band gap to produce the photoexcited electron easily. Furthermore, InSe/Te vdW heterostructure shows remarkably light absorption capacities and distinguished maximum power conversion efficiency (PCE) up to 13.39%. Our present study will inspire researchers to design vdW heterostructures for solar cell application in a purposeful way.