An Advanced Selenium-Carbon Cathode for Rechargeable Lithium-Selenium Batteries

Superhalide-Anion-Motivator Reforming-Enabled Bipolar Manipulation toward Longevous Energy-Type Zn||Chalcogen Batteries

Neutrophilic superhalide-anion-triggered chalcogen conversion-based Zn batteries, despite latent high-energy merit, usually suffer from a short lifespan caused by dendrite growth and shuttle effect. Here, a superhalide-anion-motivator reforming strategy is initiated to simultaneously manipulate the anode interface and Se conversion intermediates, realizing a bipolar regulation toward longevous energy-type Zn batteries. With ZnF2 chaotropic additives, the original large-radii superhalide zincate anion species in ionic liquid (IL) electrolytes are split into small F-containing species, boosting the formation of robust solid electrolyte interphases (SEI) for Zn dendrite inhibition. Simultaneously, ion radius reduced multiple F-containing Se conversion intermediates form, enhancing the interion interaction of charged products to suppress the shuttle effect. Consequently, Zn||Se batteries deliver a ca. 20-fold prolonged lifespan (2000 cycles) at 1 A g-1 and high energy/power density of 416.7 Wh kgSe-1/1.89 kW kgSe-1, outperforming those in F-free counterparts. Pouch cells with distinct plateaus and durable cyclability further substantiate the practicality of this design.

Unveiling the anchoring and catalytic effect of Co@C3N3 monolayer as a high-performance selenium host material in lithium-selenium batteries: a first-principles study

Suppressing the shuttle effect of high-order polyselenides is crucial for the development of high-performance host materials in lithium-selenium (Li-Se) batteries. Using first-principles calculations, the feasibility of Co@C3N3 monolayer as selenium cathode host material for Li-Se batteries is systematically evaluated from the aspects of binding energy, charge transfer mechanism, and catalytic effect of polyselenides in the present work. The Co@C3N3 monolayer can effectively prevent the solubilization of high-order polyselenides with large binding energy and charge transfer resulting from the synergistic effect of Li-N and Co-Se bonds. The polyselenides are inclined to adsorb on the surface of Co@C3N3 monolayer instead of interacting with the electrolytes, which effectively inhibits the shuttling of high-order polyselenides and improves cycling stability. The cobalt participation improves the conductivity of C3N3 monolayer, and the semi-metallic characteristics of the Co@C3N3 monolayer are maintained after the adsorption of Li2Sen (n = 1, 2, 4, 6, 8) or Se8 clusters, which is advantageous for the utilization of active selenium material. The crucial catalytic role of the Co@C3N3 monolayer is evaluated by examining the reduction pathway of Se8 and the decomposition barrier of Li2Se, and the results highlight the capability of Co@C3N3 monolayer to enhance the utilization of selenium and promote the transition of Li2Se. Our present work could not only provide valuable insights into the anchoring and catalytic effect of Co@C3N3 monolayer, but also shed light on the future investigation on the high performance C3N3-based host materials for Li-Se batteries.

Amorphous Selenium and Crystalline Selenium Nanorods Graphene Composites as Cathode Materials for All-Solid-State Lithium Selenium Batteries

Selenium (Se) is an element in the same main group as sulfur and is characterized by high electrical conductivity and large capacity (675 mAh g-1 ). Herein, a novel ultra-high dispersion amorphous selenium graphene composite (a-Se/rGO) was synthesized and a selenium nanorods graphene composite (b-Se/rGO) was prepared by hydrothermal method as the cathode material for all solid-state lithium-selenium (Li-Se) batteries, hoping to improve the efficiency and utilization rate of active substances in all solid-state batteries. The all-solid-state batteries were assembled using a heated thawing electrolyte (2LiIHPN-LiI; HPN=3-hydroxypropionitrile). The utilization rate of a-Se/rGO was 103 % and the capacity was 697 mAh g-1 , which remained at 281 mAh g-1 (41.6 % of the 675 mAh g-1 ) after 30 cycles under 0.5 C. Notably, a-Se/rGO showed excellent performance concerning its utilization rate, with a capacity of up to 610 mAh g-1 at 2 C, due to the high availability of amorphous Se and the special properties of the electrolytes. However, in the charge and discharge cycles, the second discharge capacity of a-Se/rGO was more significantly attenuated than that of the first discharge due to the formation of larger crystals of selenium during the charging process. The battery assembled using b-Se/rGO maintained a capacity of 270.58 mAh g-1 after 30 cycles (the retention rate of discharge capacity was 66.13 % compared with that in the first cycle). Through TEM and other relevant tests, it is speculated that amorphous selenium is conducive to capacity release, which, however, is affected by the formation of crystalline selenium after the first charge process.

Facile Synthesis of Carbon Nanospheres with High Capability to Inhale Selenium Powder for Electrochemical Energy Storage

Carbon–selenium composite positive electrode (CSs@Se) is engineered in this project using a melt diffusion approach with glucose as a precursor, and it demonstrates good electrochemical performance for lithium–selenium batteries. X-ray diffraction (XRD) and scanning electron microscopy (SEM) with EDS analysis are used to characterize the newly designed CSs@Se electrode. To complete the evaluation, electrochemical characterization such as charge–discharge (rate performance and cycle stability), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) tests are done. The findings show that selenium particles are distributed uniformly in mono-sized carbon spheres with enormous surface areas. Furthermore, the charge–discharge test demonstrates that the CSs@Se cathode has a rate performance of 104 mA h g⁻¹ even at current density of 2500 mA g⁻¹ and can sustain stable cycling for 70 cycles with a specific capacity of 270 mA h g⁻¹ at current density of 25 mA g⁻¹. The homogeneous diffusion of selenium particles in the produced spheres is credited with an improved electrochemical performance.

Understanding the anchoring and catalytic effect of the Co@C2N monolayer in lithium-selenium batteries: a first-principles study

The practical applications of lithium-selenium (Li-Se) batteries are impeded due to the low utilization of active selenium, sluggish kinetics, and volume change. The development of highly efficient host materials to suppress high-order polyselenide shuttling and accelerate Li₂Se conversion is essential for Li-Se batteries. Herein, a theoretical design of a Co@C₂N monolayer as a host material for ultra-high areal capacity Li-Se batteries is proposed by first-principles calculations. The investigations of the lowest energy configurations, binding energies, and the charge transfer indicate that the Co@C₂N monolayer could alleviate the reciprocating motion of high-order polyselenides and improve the cycling performance. Further electronic property calculations show that the semi-metallic characteristics of the Co@C₂N monolayer material are retained even after chemical adsorption with Se₈ or Li₂Se_n molecules, which is beneficial for the utilization of active selenium. In addition, the crucial catalytic role of the Co@C₂N monolayer is investigated and the results indicate that the Co@C₂N monolayer could facilitate the formation and decomposition of Li₂Se molecules during the discharge and charge processes. Our present work would not only provide a deep understanding on the anchoring and catalytic effect of the Co@C₂N monolayer, but also demonstrate a general principle for the rational design and screening of advanced materials for high energy density Li-Se batteries.

Nanowired NiMoO4/NiSe2/MoSe2 prepared through in situ selenylation as a high performance supercapacitor electrode

After in situ selenylation, hydrothermally synthesized NiMoO4 was partially converted to NiSe2 and MoSe2, and the obtained NiMoO4/NiSe2/MoSe2 nanowires were used as a supercapacitor electrode material. The specific capacitance of the nanowired NiMoO4/NiSe2/MoSe2 was significantly higher than that of NiMoO4 at a current density of 1 A g-1 (955 vs. 489 F g-1). NiMoO4/NiSe2/MoSe2 also exhibited a high capacitance retention of 86.1% after 5000 cycles at 10 A g-1. The high supercapacitive performance of NiMoO4/NiSe2/MoSe2 can be ascribed to the obvious heterointerfaces, rich defects and remarkably increased electrical conductivity after in situ selenylation of NiMoO4.

Electrochemistry of Electrode Materials Containing S-Se Bonds for Rechargeable Batteries

Sulfur (S) and selenium (Se) have been considered as promising high capacity cathode materials for rechargeable batteries. They have differences in their physical properties (e.g., electronic conductivity) but the same number of electrons in their outermost shells, which leads to similarity in their electrochemical behavior in batteries. In recent years, some efforts have been taken to combine them in electrodes in the hope of improved battery performance. The S-Se bonds of these electrode materials lead to unusual properties and intriguing electrochemical behavior, which have attracted increasing interest. In this Minireview, electrode materials containing S-Se bonds are summarized, including inorganic S_x Se_y solid solutions, organic compounds, and organic-inorganic hybrid materials. Our understanding in these materials is still premature, but they have shown unique properties to be electrode materials. We hope this Minireview could provide a new insight into the design, synthesis, and understanding of these materials, which could enable high energy density rechargeable batteries.

Beyond the Polysulfide Shuttle and Lithium Dendrite Formation: Addressing the Sluggish Sulfur Redox Kinetics for Practical High-Energy Li-S Batteries

Electrolyte modulation simultaneously suppresses polysulfide the shuttle effect and lithium dendrite formation of lithium-sulfur (Li-S) batteries. However, the sluggish S redox kinetics, especially under high S loading and lean electrolyte operation, has been ignored, which dramatically limits the cycle life and energy density of practical Li-S pouch cells. Herein, we demonstrate that a rational combination of selenium doping, core-shell hollow host structure, and fluorinated ether electrolytes enables ultrastable Li stripping/plating and essentially no polysulfide shuttle as well as fast redox kinetics. Thus, high areal capacity (>4 mAh cm^-2 ) with excellent cycle stability and Coulombic efficiency were both demonstrated in Li metal anode and thick S cathode (4.5 mg cm^-2 ) with a low electrolyte/sulfur ratio (10 μL mg^-1 ). This research further demonstrates a durable Li-Se/S pouch cell with high specific capacity, validating the potential practical applications.

Two-Plateau Li-Se Chemistry for High Volumetric Capacity Se Cathodes

For Li-Se batteries, ether- and carbonate-based electrolytes are commonly used. However, because of the "shuttle effect" of the highly dissoluble long-chain lithium polyselenides (LPSes, Li₂ Se_n , 4≤n≤8) in the ether electrolytes and the sluggish one-step solid-solid conversion between Se and Li₂ Se in the carbonate electrolytes, a large amount of porous carbon (>40 wt % in the electrode) is always needed for the Se cathodes, which seriously counteracts the advantage of Se electrodes in terms of volumetric capacity. Herein an acetonitrile-based electrolyte is introduced for the Li-Se system, and a two-plateau conversion mechanism is proposed. This new Li-Se chemistry not only avoids the shuttle effect but also facilitates the conversion between Se and Li₂ Se, enabling an efficient Se cathode with high Se utilization (97 %) and enhanced Coulombic efficiency. Moreover, with such a designed electrolyte, a highly compact Se electrode (2.35 g_Se  cm^-3 ) with a record-breaking Se content (80 wt %) and high Se loading (8 mg cm^-2 ) is demonstrated to have a superhigh volumetric energy density of up to 2502 Wh L^-1 , surpassing that of LiCoO₂ .

Construction of well-designed 1D selenium–tellurium nanorods anchored on graphene sheets as a high storage capacity anode material for lithium-ion batteries

The graphical illustration of the preparation of the SeTe@rGO composite material and its electrochemical application in Li-ion batteries.

A highly-effective nitrogen-doped porous carbon sponge electrode for advanced K–Se batteries

A rechargeable K–Se battery is emerging as an energy storage system because of its much higher specific capacity than that of the traditional alkali metal-ion batteries, but is facing some critical issues and challenges.

Iodine encapsulated in mesoporous carbon enabling high-efficiency capacitive potassium-Ion storage

The development of potassium-ion batteries (KIBs) are hampered by the lack of appropriate electrode materials allowing for the reversible insertion/de-insertion of the large K-ion. Iodine, as a conversion-type cathode for rechargeable batteries, has high theoretical capacity and excellent electrochemical reversibility, making it a potential cathode material for KIBs. However, due to the defects of iodine with the poor electronic conductivity and easy dissolution in the electrolyte, an intensive quest for iodine-based KIBs enabling high-performance potassium-ion storage is still underway. In this work, a high-efficiency capacitive K-I₂ battery has been successfully achieved by constructing a nanocomposite of iodine encapsulated in mesoporous carbon (CMK-3). The as-prepared CMK-3/iodine nanocomposite exhibites excellent rate performance (89.3 mA h g^-1 at 0.5 A g^-1) and superior cycling stability, which remarkably exceeds most of reported KIBs cathode materials. Such a excellent electrochemical performance can be ascribed to the engineered structure of CMK-3/iodine hybridized electrode which can alleviate the impact of the shuttle phenomenon, improve electronic conductivity and facilitate ion diffusion. As a consequence, iodine within the conductive protecting CMK-3 can afford an extraordinary pseudo-capacitive potassium-ion storage, which sheds light on the development prospect of conversion-type electrode materials to meet urgent demand for advanced KIBs.

Encapsulation of SeS2 into Nitrogen-Doped Free-Standing Carbon Nanofiber Film Enabling Long Cycle Life and High Energy Density K-SeS2 Battery

K-SeS₂ batteries could provide a low-cost and high energy density energy storage system, because the earth-abundant element potassium (K) shows a low reduction potential and a high gravimetric capacity. But the K-SeS₂ battery has never been reported because of the lack of high-performance electrode materials. Herein, we design an advanced K-SeS₂ battery by encapsulation of SeS₂ in the nitrogen-doped free-standing porous carbon matrix (SeS₂@NCNFs). The self-supported SeS₂@NCNFs electrode achieves a high reversible capacity of 417 mAh g^-1 after 1000 cycles with 85% capacity retention at 0.5 Ag^1- with nearly 100% Coulombic efficiency. The nanosized SeS₂ nanoparticles are encapsulated in the carbon matrix, which minimizes the volume expansion during cycling and shortens the ion transport pathways, thus enhancing the rate capability. The interconnected porous carbon nanofiber structure could improve the flexibility and offer a continuous pathway for rapid ionic/electronic transport. The DFT calculations confirm that high content N-doping (11.2 at. %) can enhance the chemical affinity between the discharge product and the N-doped carbon. The pyrrolic and pyridinic N-doping lead to stronger adsorption than that of the graphitic N-doping. This proposed design holds great promise for practical application of high energy density K-SeS₂ batteries.

A Se-hollow porous carbon composite for high-performance rechargeable K–Se batteries

In this study, a novel hollow carbon matrix was designed and prepared using a facile NaCl crystal template for the effective encapsulation of Se.

CNT Interwoven Nitrogen and Oxygen Dual-Doped Porous Carbon Nanosheets as Free-Standing Electrodes for High-Performance Na-Se and K-Se Flexible Batteries

Na-Se and K-Se batteries are attractive as a stationary energy storage system because of much abundant resources of Na and K in the Earth's crust. As the alloy-type Se has a severe pulverization issue, one critical challenge to develop advanced Na-Se and K-Se batteries is to explore a highly efficient and stable Se-based cathode. Herein, a flexible free-standing Se/carbon composite film is prepared by encapsulation of Se into a carbon nanotube (CNT) interwoven N,O dual-doped porous carbon nanosheet (Se@NOPC-CNT). The 3D interconnected CNT uniformly wrapped on the N,O dual-doped porous carbon skeletons improves the flexibility and offers an interconnected conductive pathway for rapid ionic/electronic transport. In addition, the N,O dual-doping significantly enhances the chemical affinity and adhesion between Na_x Se/K_x Se (0 < x ≤ 2) and porous carbon, which is confirmed by density functional theory calculation. When used as the cathode in Na-Se batteries, the Se@NOPC-CNT delivers a remarkable reversible capacity of 400 mA h g^-1 at 1 A g^-1 after 2000 cycles with a 0.008% capacity decay per cycle. For K-Se batteries, it also exhibits an excellent cycling stability (335 mA h g^-1 after 700 cycles at 0.8 A g^-1 ). This unique design may open an avenue for practical application of flexible Na-Se and K-Se batteries.

Metal Oxide Interlayer for Long-Lived Lithium-Selenium Batteries

A lithium-selenium (Li-Se)-alkali activated carbon hybrid cell with a tungsten oxide interlayer is implemented for the first time. The Se hybrid at a Se loading of 70 % in the full Li-Se cell delivers a large reversible capacity of 625 mA h g_Se ^-1 , in comparison with 505.8 mA h g_Se ^-1 achieved for the pristine Se cell. This clearly shows the advantage of the carbon in improving the capacity of the Li-Se cell. A tungsten oxide interlayer is drop-cast over the battery separator to further circumvent the issues of polyselenide dissolution and shuttle, which cause severe capacity fading. The oxide layer conducts Li ions, as evidenced from the Li-ion diffusion coefficient of 4.2×10^-9  cm²  s^-1 , and simultaneously blocks the polyselenide crossover, as it is impermeable to polyselenides, thereby reducing the capacity fading with cycling. The outcome of this unique approach is reflected in the reversible capacities of 808 and 510 mA h g_Se ^-1 achieved for the Li-oxide@separator/Se-alkali activated carbon cell before and after 100 cycles, respectively, thus demonstrating that carbon and oxide can efficiently restrict the capacity fading and improve the performances of Li-Se cells.

Mesoporous Carbon@Titanium Nitride Hollow Spheres as an Efficient SeS2 Host for Advanced Li-SeS2 Batteries

The introduction of a certain proportion of selenium into sulfur-based cathodes is an effective strategy for enhancing the integrated battery performance. However, similar to sulfur, selenium sulfide cathodes suffer from poor cycling stability owing to the dissolution of reaction intermediate products. In this study, to exploit the advantages of SeS₂ to the full and avoid its shortcomings, we designed and synthesized a hollow mesoporous carbon@titanium nitride (HMC@TiN) host for loading 70 wt % of SeS₂ as a cathode material for Li-SeS₂ batteries. Benefiting from both physical and chemical entrapment by hollow mesoporous carbon and TiN, the HMC@TiN/SeS₂ cathode manifests high utilization of the active material and excellent cycling stability. Moreover, it exhibits promising areal capacity (up to 4 mAh cm^-2 ) with stable cell performance in the high-mass-loading electrode.

Tin Selenides with Layered Crystal Structures for Li-Ion Batteries: Interesting Phase Change Mechanisms and Outstanding Electrochemical Behaviors

Tin selenides with layered crystal structures, SnSe and SnSe₂, were synthesized by a solid-state method and electrochemically tested for use as Li-ion battery anodes. The phase change mechanisms of these compounds were thoroughly evaluated by ex situ X-ray diffraction and Se K-edge extended X-ray absorption fine structure techniques. SnSe showed better electrochemical reversibility of Li insertion/extraction than SnSe₂, which was attributed to remarkable conversion/recombination reactions of the former compound during lithiation/delithiation. Additionally, the electrochemical performance of SnSe was further enhanced by preparing carbon-modified nanocomposites using two different methods, that is, heat treatment (HT) for producing a carbon coating using polyvinyl chloride as a precursor and high-energy ball milling (BM) using carbon black powder. The SnSe/C electrode produced by BM showed a highly reversible initial capacity of 726 mA h g^-1 with a good initial Coulombic efficiency of ∼82%, excellent cycling behavior (626 mA h g^-1 after 200 cycles), and a fast C-rate performance (580 mA h g^-1 at 2C rate).

A Se/C composite as cathode material for rechargeable lithium batteries with good electrochemical performance

A Se/C composite is prepared as cathode material for rechargeable lithium batteries, which significantly enhances the capacity and improves the rate capability in comparison with the commercial Se particles.

Lithium-sulfur batteries: electrochemistry, materials, and prospects

With the increasing demand for efficient and economic energy storage, Li-S batteries have become attractive candidates for the next-generation high-energy rechargeable Li batteries because of their high theoretical energy density and cost effectiveness. Starting from a brief history of Li-S batteries, this Review introduces the electrochemistry of Li-S batteries, and discusses issues resulting from the electrochemistry, such as the electroactivity and the polysulfide dissolution. To address these critical issues, recent advances in Li-S batteries are summarized, including the S cathode, Li anode, electrolyte, and new designs of Li-S batteries with a metallic Li-free anode. Constructing S molecules confined in the conductive microporous carbon materials to improve the cyclability of Li-S batteries serves as a prospective strategy for the industry in the future.