Anchoring and catalytic insights into bilayer C4N3 material for lithium-selenium batteries: a first-principles study

In the present work, a theoretical design for the viability of bilayer C4N3 (bi-C4N3) as a promising host material for Li-Se battery was conducted utilizing first-principles calculations. The AA- and AB-stacking configurations of bilayer C4N3 can effectively inhibit the shuttling of high-order polyselenides through the synergistic effect of physical confinement and strong Li-N bonds. Compared to conventional electrolytes, the AA- and AB-stacking bilayer C4N3 demonstrate enhanced adsorption capabilities for the polyselenides. The anchored structures of Se8 or Li2Sen (n = 1, 2, 4, 6, 8) molecules within the bilayer C4N3 exhibit high electrical conductivities, which are beneficial for enhancing the electrochemical performance. The catalytic effects of AA- and AB-stacking bilayer C4N3 were investigated by the reduction of Se8 and the energy barrier associated with the decomposition of Li2Se. The AA- and AB-stacking bilayer C4N3 can significantly decrease the activation barrier and promote the decomposition of Li2Se. The mean square displacement (MSD) curves reveal the pronounceably sluggish Li-ions diffusions in polyselenides within the AA- and AB-stacking bilayer C4N3, which in turn demonstrates the notable prospects in mitigating the shuttle effect.

Synthesis and characterization of nanostructured graphene-doped selenium

In this work, we explore various properties of elemental selenium glass (g-Se) by doping with graphene through the facile melt-quench technique. The structural information of the synthesized sample was found by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Raman spectroscopy. The analyses confirm that the graphene-doped g-Se behaves like a glass-ceramic material. Electrical and dielectric measurements were performed to discover the consequences of graphene incorporation on the nano-structure of g-Se. The electrical measurements of the dielectric parameters (i.e., dielectric constant ε' and loss ε'') and conductivity (σ _ac) reveal that graphene incorporation causes a rise in the dielectric constant but simultaneously increases dielectric loss. The enhancement in ε' and ε'' values is thought to be a consequence of the interface effect between graphene and the host selenium glass. Calorimetric experiments were performed in a standard differential scanning calorimetry (DSC) unit on the glassy nanocomposite in non-isothermal mode. By measuring the kinetic temperatures at four heating rates, the kinetics of the crystallization/glass transition were studied. The results were examined to understand the role of graphene doping on the well-known phase transitions (i.e., glass transition and crystallization) of g-Se.

Recent Advancements in Selenium-Based Cathode Materials for Lithium Batteries: A Mini-Review

Selenium (Se)-based cathode materials have garnered considerable interest for lithium-ion batteries due to their numerous advantages, including low cost, high volumetric capacity (3268 mAh cm−3), high density (4.82 g cm−3), ability to be cycled to high voltage (4.2 V) without failure, and environmental friendliness. However, they have low electrical conductivity, low coulombic efficiency, and polyselenide solubility in electrolytes (shuttle effect). These factors have an adverse effect on the electrochemical performance of Li-Se batteries, rendering them unsuitable for real-world use. In this study, we briefly examined numerous approaches to overcoming these obstacles, including selecting an adequate electrolyte, the composition of Se with carbonaceous materials, and the usage of metal selenide base electrodes. Furthermore, we examined the effect of introducing interlayers between the cathode and the separator. Finally, the remaining hurdles and potential study prospects in this expanding field are proposed to inspire further insightful work.

Unraveling the superior anchoring of lithium polyselenides to the confinement bilayer C2N: an efficient host material for lithium-selenium batteries

Carbonaceous materials with pores or bilayer spaces are a kind of potential host material to confine polyselenide diffusion and mitigate the shuttling effect. In the present work, a theoretical design of bilayer C₂N (bi-C₂N) as an efficient host material for lithium-selenium (Li-Se) batteries was explored by first-principles calculations. AA- and AB-stacking bilayer C₂N could alleviate the dissolution of high-order polyselenides through a synergistic effect of physical confinement and strong Li-N bonds. Lithium polyselenides prefer to anchor on AA- and AB-stacking bilayer C₂N instead of the commonly used electrolytes, showing their capabilities in suppressing the shuttle effect. Charge transfer occurs from Se₈ and Li₂Se_n molecules (LiPSes) to AA- and AB-stacking bilayer C₂N, giving rise to the formation of strong Li-N bonds. The AA- and AB-stacking LiPSes@C₂N systems possess high electrical conductivities, which is beneficial for high electrochemical performance. In addition, the reversible conversion mechanisms of Li₂Se_n in the AA- and AB-stacking bilayer C₂N are also investigated through the energy changes and decomposition reaction of the Li₂Se molecule, and the results indicate that AA- and AB-stacking bilayer C₂N facilitate the formation and decomposition of Li₂Se by decreasing the active energy barriers and improving the selenium utilization rates. Our present work could shed some light on a possible strategy for designing highly efficient bilayer host materials for high performance Li-Se batteries.

Durable Lithium/Selenium Batteries Enabled by the Integration of MOF-Derived Porous Carbon and Alucone Coating

Lithium-selenium (Li-Se) batteries are a promising energy storage system in electric vehicles due to their high capacity and good kinetics. However, the shuttle effect issue, caused by polyselenide dissolution from the Se cathode, has hampered the development of Li-Se batteries. Herein, we developed a facile preparation of porous carbon from a metal-organic framework (MOF) to confine Se (Se/CZIF) and protect the Se/CZIF composite with an alucone coating by molecular layer deposition (MLD). The optimal alucone coated Se/CZIF cathode prepared exhibits a one-step reversible charge/discharge process in the carbonate electrolytes. The inhibition of polyselenide dissolution is credited with the improved electrochemical performance, formation of thin and stable solid electrolyte interphase (SEI) layers, and a reduction in charge transfer resistance, thus improving the overall performance of Li-Se batteries.

State-Of-The-Art and Future Challenges in High Energy Lithium-Selenium Batteries

Li-chalcogen batteries, especially the Li-S batteries (LSBs), have received paramount interests as next generation energy storage techniques because of their high theoretical energy densities. However, the associated challenges need to be overcome prior to their commercialization. Elemental selenium, another chalcogen member, would be an attractive alternative to sulfur owing to its higher electronic conductivity, comparable capacity density, and moreover, excellent compatibility with carbonate electrolytes. Unlike LSBs, the research and development of Li-Se batteries (LSeBs) have garnered burgeoning attention but are still in their infant stage, where a comprehensive yet in-depth overview is highly imperative to guide future research. Herein, a critical review of LSeBs, in terms of the underlying mechanisms, cathode design, blocking layer engineering, and emerging solid-state electrolytes is provided. First, the electrolyte-dependent electrochemistry of LSeBs is discussed. Second, the advances in Se-based cathodes are comprehensively summarized, especially highlighting the state-of-the-art Se_x S_y cathodes, and mainly focusing on their structures, compositions, and synthetic strategies. Third, the versatile separators/interlayers optimization and interface regulation are outlined, with a particular focus on the emerging solid-state electrolytes for advanced LSeBs. Last, the remaining challenges and research orientations in this booming field are proposed, which are expected to motivate more insightful works.

Melamine-based polymer networks enabled N, O, S Co-doped defect-rich hierarchically porous carbon nanobelts for stable and long-cycle Li-ion and Li-Se batteries

Li-Se battery is a promising energy storage candidate owing to its high theoretical volumetric capacity and safe operating condition. In this work, for the first time, we report using the whole organic Melamine-based porous polymer networks (MPNs) as a precursor to synthesize a N, O, S co-doped hierarchically porous carbon nanobelts (HPCNBs) for both Li-ion and Li-Se battery. The N, O, S co-doping resulting in the defect-rich HPCNBs provides fast transport channels for electrolyte, electrons and ions, but also effectively relieve volume change. When used for Li-ion battery, it exhibits an advanced lithium storage performance with a capacity of 345 mAh g^-1 at 500 mA g^-1 after 150 cycles and a superior rate capacity of 281 mAh g^-1 even at 2000 mA g^-1. Further density function theory calculations reveal that the carbon atoms adjacent to the doping sites are electron-rich and more effective to anchor active species in Li-Se battery. With the hierarchically porous channels and the strong dual physical-chemical confinement for Li₂Se, the Se@ HPCNBs composite delivers an ultra-stable cycle performance even at 2 C after 1000 cycles. Our work here suggests that introduce of heteroatoms and defects in graphite-like anodes is an effective way to improve the electrochemical performance.

Stabilization of Li-Se Batteries by Wearing PAN Protective Clothing

Lithium-selenium (Li-Se) batteries have recently attracted more and more attentions as new secondary battery systems due to the similarity but better performances than lithium-sulfur (Li-S) batteries. However, the dissolution of selenium in electrolytes results in low selenium utilization, concentration polarization, inferior capacities, and unstable cycling performances. Herein, 46.58 wt% of selenium is loaded on carbon cloths through the calcination process, which were directly used as self-supporting cathodes. Carbonized polyacrylonitrile (PAN) nanofiber membranes produced by electrospinning are worn as the protective clothing between the cathode and separator to avoid the loss and dissolution of selenium. The stabilization of Li-Se batteries was enhanced by introducing two interlayers, as expected, they exhibit a stable reversible average capacity of 590 mA h g^-1 during 1000 cycles at a current density of 0.5 C (1 C = 675 mA g^-1). No polyselenide formation is found during charging/discharging, and the effects of the introduced PAN interlayers on improving the stability and reducing the polarization of the assembled Li-Se batteries are confirmed by mechanistic characterizations. These regulated Li-Se batteries present great application potential in the future, and the design idea can also be promoted to explore other energy storage systems.

Free-Standing Selenium Impregnated Carbonized Leaf Cathodes for High-Performance Sodium-Selenium Batteries

A novel approach of carbonizing leaves by thermal pyrolysis with melt diffusion followed by selenium vapor deposition is developed to prepare the carbon-selenium composite cathodes for sodium-selenium batteries. The carbonized leaf possesses internal hierarchical porosity and high mass loading; therefore, the composite is applied as a binder- and current collector-free cathode, exhibiting an excellent rate capability and a high reversible specific capacity of 520 mA h g^-1 at 100 mA g^-1 after 120 cycles and 300 mA h g^-1 even at 2 A g^-1 after 500 cycles without any capacity loss. Moreover, the unique natural three-dimensional structure and moderate graphitization degree of leaf-based carbon facilitate Na⁺/e^- transport to activate selenium which can guarantee a high utilization of the selenium during discharge/charge process, demonstrating a promising strategy to fabricate advanced electrodes toward the sodium-selenium batteries.

Robust and Conductive Red MoSe2 for Stable and Fast Lithium Storage

Two-dimensional (2D) layered transition-metal dichalcogenides (LTMDs) display various crystal phases with distinct symmetries, structures, and physical properties. Exploring and designing different structural phases in two dimensions could provide an avenue for switching material properties, aiming at practical applications for potential fields. Here we demonstrate a conceptually designed approach to narrow the band gap of MoSe₂ and obtain a conductive red MoSe₂ nanosheet. By introducing the high valence state of Mo species and constructing the Mo-O bonding on the surface of the MoSe₂ nanosheets, the electronic properties can be modified and the conductivity is accordingly improved, an effect that significantly improves their lithium storage capacity and high-rate capability. We anticipate that the exploration of the conductive red MoSe₂ with tunable band gap could help us unlock more potential crystal structures of LTMD-based and even other 2D materials for further applications.

Highly Reversible Li-Se Batteries with Ultra-Lightweight N,S-Codoped Graphene Blocking Layer

The desire for practical utilization of rechargeable lithium batteries with high energy density has motivated attempts to develop new electrode materials and battery systems. Here, without additional binders we present a simple vacuum filtration method to synthesize nitrogen and sulfur codoped graphene (N,S-G) blocking layer, which is ultra-lightweight, conductive, and free standing. When the N,S-G membrane was inserted between the catholyte and separator, the lithium-selenium (Li-Se) batteries exhibited a high reversible discharge capacity of 330.7 mAh g^-1 at 1 C (1 C = 675 mA g^-1) after 500 cycles and high rate performance (over 310 mAh g^-1 at 4 C) even at an active material loading as high as ~ 5 mg cm^-2. This excellent performance can be ascribed to homogenous dispersion of the liquid active material in the electrode, good Li⁺-ion conductivity, fast electronic transport in the conductive graphene framework, and strong chemical confinement of polyselenides by nitrogen and sulfur atoms. More importantly, it is a promising strategy for enhancing the energy density of Li-Se batteries by using the catholyte with a lightweight heteroatom doping carbon matrix.

Recent Progress in the Design of Advanced Cathode Materials and Battery Models for High-Performance Lithium-X (X = O2 , S, Se, Te, I2 , Br2 ) Batteries

Recent advances and achievements in emerging Li-X (X = O₂ , S, Se, Te, I₂ , Br₂ ) batteries with promising cathode materials open up new opportunities for the development of high-performance lithium-ion battery alternatives. In this review, we focus on an overview of recent important progress in the design of advanced cathode materials and battery models for developing high-performance Li-X (X = O₂ , S, Se, Te, I₂ , Br₂ ) batteries. We start with a brief introduction to explain why Li-X batteries are important for future renewable energy devices. Then, we summarize the existing drawbacks, major progress and emerging challenges in the development of cathode materials for Li-O₂ (S) batteries. In terms of the emerging Li-X (Se, Te, I₂ , Br₂ ) batteries, we systematically summarize their advantages/disadvantages and recent progress. Specifically, we review the electrochemical performance of Li-Se (Te) batteries using carbonate-/ether-based electrolytes, made with different electrode fabrication techniques, and of Li-I₂ (Br₂ ) batteries with various cell designs (e.g., dual electrolyte, all-organic electrolyte, with/without cathode-flow mode, and fuel cell/solar cell integration). Finally, the perspective on and challenges for the development of cathode materials for the promising Li-X (X = O₂ , S, Se, Te, I₂ , Br₂ ) batteries is presented.

Advanced cathode materials for lithium-ion batteries using nanoarchitectonics

In recent years, the global climate has further deteriorated because of the excessive consumption of traditional energy sources. The replacement of traditional fossil fuels with limited reserves by alternative energy sources has become one of the main strategies to alleviate the increasingly serious environmental issues. As a sustainable and promising store of renewable energy, lithium-ion batteries have replaced other types of batteries for many small-scale consumer devices. Notwithstanding their worldwide applications, it has become abundantly clear that the design and fabrication of electrode materials is urgently required to adapt to meet the growing global demand for energy and the power densities needed to make electric vehicles fully commercially viable. To dramatically enhance battery performance, further advances in materials chemistry are essential, especially in novel nanomaterials chemistry. The construction of nanostructured cathode materials by reducing particle size can boost electrochemical performance. The present review is intended to provide readers with a better understanding of the unique contribution of various nanoarchitectures to lithium-ion batteries over the last decade. Nanostructured cathode materials with different dimensions (0D, 1D, 2D, and 3D), morphologies (hollow, core-shell, etc.), and composites (mainly graphene-based composites) are highlighted, aiming to unravel the opportunities for the development of future-generation lithium-ion batteries. The advantages and challenges of nanomaterials are also addressed in this review. We hope to simulate many more extensive and insightful studies on nanoarchitectonic cathode materials for advanced lithium-ion batteries with desirable performance.