Role of Ferroelectric In2Se3 in Polysulfide Shuttling and Charging/Discharging Kinetics in Lithium/Sodium-Sulfur Batteries

Coordination Engineering of Fe-Centered Catalysts for Superior Li-S Battery Performance

Iron-nitrogen functionalized graphene has emerged as a promising cathode host for rechargeable lithium-sulfur batteries (RLSBs) due to its affordability and enhanced battery performance. To optimize its catalytical efficiency, we propose a novel approach involving coordination engineering. Our investigation spans a plethora of catalysts with varied coordination environments, focusing on elements B, C, N and O. We revealed that Fe-C4 and Fe-B2C2-h are particularly effective for promoting Li2S oxidation, whereas Fe-N4 excels in catalyzing the sulfur reduction reaction (SRR). Importantly, our study identified specific descriptors - namely, the Integrated Crystal Orbital Hamilton Population (ICOHP) and the bond length between Fe and S in Li2S adsorbed state - as the most effective predictive descriptors for Li2S oxidation barriers. Meanwhile, Li2S adsorption energy emerges as a reliable descriptor for assessing the SRR barrier. These identified descriptors are expected to be instrumental in rapidly identifying promising cathode hosts across various metal-centered systems with diverse coordination environments. Our findings not only offer valuable insights into the role of coordination environment, but also present an effective path for rapidly identifying high performance catalysts for RLSBs, enabling the acceleration of advanced RLSBs development.

Theoretical evaluation of monolayer MA2Z4 (M = Ti, Zr, or Hf; A = Si or Ge; and Z = P or As) family as promising candidates for lithium-sulfur batteries

Rechargeable lithium-sulfur (Li-S) batteries have been considered as a potential energy storage system due to their high theoretical specific energy. However, their practical commercial application has been hindered by unresolved key issues. One promising approach to overcoming these challenges is the development of anchoring materials with exceptional performance. In this work, we conducted detailed evaluations of twelve types of MA2Z4 (M = Ti, Zr, or Hf; A = Si or Ge; and Z = P or As) monolayers as potential Li-S battery electrodes through first-principles calculations. Our results indicate that these monolayers can effectively immobilize Li2Sn species, preventing them from dissolving into the electrolyte and preserving intact Li2Sn conformations. The high electrical conductivity of these monolayers can be perfectly retained after S8/L2Sn clusters adsorption. Furthermore, the MA2P4 monolayers demonstrate superior catalytic performance for the sulfur reduction reaction (SRR) compared to the MA2As4 counterparts, whereas the MA2As4 monolayers exhibit lower decomposition energy barriers. Our current work indicates that these MA2Z4 monolayers hold significant promise as electrode materials for Li-S batteries.

The "d-p orbital hybridization"-guided design of novel two-dimensional MOFs with high anchoring and catalytic capacities in Lithium - Sulfur batteries

The energy system of lithium-sulfur batteries is quite promising, however, lithium-sulfur batteries still suffer from considerable problems, such as the abominable shuttle effect of polysulfides (LiPSs), the low conductivity of the solid-phase products, the slow redox kinetics during charging and discharging, and the volume expansion. Herein, the hybridization pattern between the d-orbitals of various transition metal atoms and the p-orbitals of sulfides is revealed grounded in the theory of density function, which explains the high adsorption strength of two-dimensional metal-organic frameworks (MOFs) with LiPSs and accelerates the screening of high-performance anchoring and catalytic materials. The results elucidate that the coordinated transition metal-organic frameworks (Mo-NH MOF) monolayers increase the capacity of LiPSs to anchor by forming more π-bonds from the hybridization of the S p orbitals and Mo d orbitals. Notably, Mo-NH MOF exhibits bifunctional catalytic activity for sulfur reduction as well as Li2S decomposition reactions during charging and discharging, which improves the conversion efficiency of redox reactions. As a result, new MOF materials featuring unique active centers and the potential mechanism by which the active centers modulate the performance of the substrate materials are revealed, and this finding may accelerate the development of high-performance Li-S batteries.

Single-atom catalysts based on C2N for sulfur cathodes in Na-S batteries: a first-principles study

Several major roadblocks, including the "shuttle effect" caused by the dissolved higher-order sodium polysulfides (NaPSs), extremely poor conductivity of sulfur cathodes, and sluggish conversion kinetics of charging-discharging reactions, have hindered the commercialization of sodium-sulfur batteries (NaSBs). In our study, representative C2N-based single-atom catalysts (SACs), TM@C2N (TM = Fe, Ni and V), are proposed to improve the comprehensive performance of NaSBs. Based on first-principles calculations, we first discuss in detail the anchoring behavior of all adsorption systems, TM@C2N/(S8 and NaPSs). The results indicate that compared to pristine C2N, TM@C2N substrates exhibit a stronger capability to capture S8/NaPSs clusters through physical/chemical binding, with V@C2N showing the most outstanding capability ranging from -2.37 to -5.03 eV. The density of states analysis reveals that metallic properties can be well maintained before and after adsorption of polysulfides. More importantly, TM@C2N configurations can greatly reduce the energy barriers of charging and discharging reactions, thereby accelerating the conversion efficiency of NaSBs. It is worth mentioning that V@C2N has lower charge-discharge energy barriers and Na ion migration rates, since the embedded TM atom weakens the strong binding of Na+ in the N6 cavity of C2N. The intrinsic mechanism analysis reveals that the interaction between the d orbitals of V and the p orbitals of S leads to the weakening of Na-S bonds, which can not only effectively inhibit the shuttle effect, but also promote the dissociation of Na2S. Overall, this work not only offers excellent catalytic materials, but also provides vital guidance for designing SACs in NaSBs.

Phosphorus-Doped Multilayer In6Se7: The Study of Structural, Electrical, and Optical Properties for Junction Device

This work investigates the characteristic of layered In6Se7 with varying phosphorus (P) dopant concentrations (In6Se7:P) from P = 0, 0.5, 1, to P = 5%. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses indicate that the structure and morphology of the In6Se7:P series compounds remain unchanged, exhibiting a monoclinic structure. Room-temperature micro-Raman (μRaman) result of all the compositions of layered In6Se7:P reveals two dominant peaks at 101 ± 3 cm-1 (i.e., In-In bonding mode) and 201 ± 3 cm-1 (i.e., Se-Se bonding mode) for each P composition in In6Se7. An extra peak at approximately 171 ± 2 cm-1 is observed and it shows enhancement at the highest P composition of In6Se7:P 5%. This mode is attributed to P-Se bonding caused by P doping inside In6Se7. All the doped and undoped In6Se7:P showed n-type conductivity, and their carrier concentrations increased with the P dopant is increased. Temperature-dependent resistivity revealed a reduction in activation energy (for the donor), as the P content is increased in the In6Se7:P samples. Kelvin probe measurement shows a decrease in work function (i.e., an energy increase of Fermi level) of the n-type In6Se7 multilayers with the increase of P content. The indirect and direct band gaps for all of the multilayer In6Se7:P of different P composition are identical. They are determined to be 0.732 eV (indirect) and 0.772 eV (direct) obtained by microtransmittance and microthermoreflectance (μTR) measurements. A rectified n-n+ homojunction was formed by stacking multilayered In6Se7/In6Se7:P 5%. The built-in potential is about Vbi ∼ 0.15 V. It agrees well with the work function difference between the two layer compounds.

Boosting Polysulfide Redox Kinetics by Temperature-Induced Metal-Insulator Transition Effect of Tungsten-Doped Vanadium Dioxide for High-Temperature Lithium-Sulfur Batteries

The practical application of Li-S batteries is still severely restricted by poor cyclic performance caused by the intrinsic polysulfides shuttle effect, which is even more severe under the high-temperature condition owing to the inevitable increase of polysulfides' solubility and diffusion rate. Herein, tungsten-doped vanadium dioxide (W-VO2 ) micro-flowers are employed with first-order metal-insulator phase transition (MIT) property as a robust and multifunctional modification layer to hamper the shuttle effect and simultaneously improve the thermotolerance of the common separator. Tungsten doping significantly reduces the transition temperature from 68 to 35 °C of vanadium dioxide, which renders the W-VO2 easier to turn from the insulating monoclinic phase into the metallic rutile phase. The systematic experiments and theoretical analysis demonstrate that the temperature-induced in-suit MIT property endows the W-VO2 catalyst with strong chemisorption against polysulfides, low energy barrier for liquid-to-solid conversion, and outstanding diffusion kinetics of Li-ion under high temperatures. Benefiting from these advantages, the Li-S batteries with W-VO2 modified separator exhibit significantly improved rate and long-term cyclic performance under 50 °C. Remarkably, even at an elevated temperature (80 °C), they still exhibit superior electrochemical performance. This work opens a rewarding avenue to use phase-changing materials for high-temperature Li-S batteries.

Fast Polysulfide Conversion Catalysis and Reversible Anode Operation by A Single Cathode Modifier in Li-Metal Anode-Free Lithium-Sulfur Batteries

The two major issues confronting the commercialization of rechargeable lithium-sulfur (Li-S) batteries are the sluggish kinetics of the sulfur electrochemical reactions on the cathode and inadequate lithium deposition/stripping reversibility on the anode. They are commonly mitigated with additives designed specifically for the anode and the cathode individually. Here, we report the use of a single cathode modifier, In2 Se3 , which can effectively catalyse the polysulfide reactions on the cathode, and also improve the reversibility of Li deposition and removal on the anode through a LiInS2 /LiInSe2 containing solid electrolyte interface formed in situ by the Se and In ions dissolved in the electrolyte. The amounts of dissolved Se and In are small relative to the amount of In2 Se3 administered. The benefits of using this single modification approach were verified in Li-metal anode-free Li-S batteries with a Li2 S loading of 4 mg cm-2 and a low electrolyte/Li2 S ratio of 7.5 μL mg-1 . The resulting battery showed 60 % capacity retention after 160 cycles at the 0.2 C rate and an average Coulombic efficiency of 98.27 %, comparing very well with recent studies using separate electrode modifiers.

Rationalizing Functionalized MXenes as Effective Anchor Materials for Lithium-Sulfur Batteries via First-Principles Calculations

The practical application of Li-S batteries has been greatly hindered by severe shuttle effects and sluggish kinetics. Anchoring soluble lithium polysulfides (LiPSs) onto host materials by chemisorption is an effective strategy for extending battery life. In this work, we performed systematic density functional theory calculations to evaluate the anchoring performance of O/F-covered MXene (M₂TC₂) in lithium-sulfur batteries. Our results indicate that the moderate anchoring strength (∼2.5 eV), outstanding sulfur reduction performance (U_L > -0.6 V), and low lithium ion diffusion barrier (<0.2 eV) of Mo₂CF₂ and V₂CF₂ make them promising host materials for LiPSs. We further revealed the determinants of the strength of binding of LiPSs to M₂CT₂. On the basis of the strong correlation among Q_M, χ_O/F, and E_a, we established a "structure-property" equation to reveal the active origin of M₂CT₂. We expect that the framework established in this work will accelerate the development of Li-S batteries.

Energy Storage Mechanism of C12-3-3 with High-Capacity and High-Rate Performance for Li/Mg Batteries

The low specific capacity and Mg non-affinity of graphite limit the energy density of ion rechargeable batteries. Here, we first identify that the monolayer C12-3-3 in sp2-sp3 carbon hybridization with high Li/Mg affinity is an appropriate anode material for Li-ion batteries and Mg-ion batteries via the first-principles simulations. The monolayer C12-3-3 can achieve high specific capacities of 1181 mAh/g for Li and 739 mAh/g for Mg, higher than those of most previous anodes. The Li storage reaction is an "adsorption-conversion-intercalation mechanism", while the Mg storage reaction is an "adsorption mechanism". The 2D carbon material of C12-3-3 displays fast diffusion kinetics with low diffusion barriers of 0.41 eV for Li and 0.21 eV for Mg. As a new carbon-based anode material, the monolayer C12-3-3 will promote the practical application of batteries with high-capacity and high-rate performance.