Se Cathode Research Articles

High‐Capacity, Long‐Life All‐Solid‐State Lithium–Selenium Batteries Enabled by Lithium Iodide Active Additive

AbstractSelenium (Se) shows promise as a cathode candidate for all‐solid‐state lithium (Li) batteries due to its impressive theoretical volumetric energy density, much higher electronic conductivity, and improved safety in comparison to those for sulfur (S). An active cathode additive, lithium iodide (LiI) is demonstrated, to address the major challenge for all‐solid‐state Li–Se batteries, namely the sluggish redox kinetics resulting from the huge solid‐state conversion barrier. The LiI additive enhances Li+ transport and provides catalytic sites for Se cathode, thus endowing the batteries with accelerated reaction kinetics and extra capacity. DFT calculation and experimental analysis clearly reveal that LiI additive efficiently accelerates the conversion between polyselenide intermediates and Li2Se. With the above advantages, the battery with LiI using Li6PS5Br electrolyte gives an outstanding capacity of 862 mAh gSe−1 beyond the theoretical specific capacity of Se and a superlong life over 1800 cycles at 1C under room temperature. This work offers a simple strategy to facilitate the kinetics of all‐solid‐state Se cathodes and paves the way for the practicality of high‐capacity and long‐life all‐solid‐state Li–Se batteries.

Biometabolically Derived Selenium Nanoparticles Armed with Protein Protective Suit toward High-Performance Li-Se Batteries.

Selenium (Se) serves as a burgeoning high-energy-density cathode material in lithium-ion batteries. However, the development of Se cathode is strictly limited by low Se utilization and inferior cycling stability arising from intrinsic volume expansion and notorious shuttle effect. Herein, a microbial metabolism strategy is developed to prepare "functional vesicle-like" Se globules via Bacillus subtilis subsp. from selenite in sewage, in which Se nanoparticles are armed with a natural biological protein membrane with rich nitrogen and phosphorus, achieving the eco-efficient conversion of trash into treasure (selenite, SeO3 2- → Selenium, Se). The appealing-design "functional vesicle-like" Se globules are beneficial to accommodate volume changes of Se in electrochemical reactions, confining polyselenides via chemisorption, and enhancing mechanical strength of electrode by associated bacteria debris, realizing comprehensive utilization of microorganism. By conceptualizing "functional vesicle-like" Se globules, rather than artificial Se-host composites, as cathode for lithium-selenium batteries, it exhibits outstanding cycling stability and improved rate performance. This strategy opens the door to design smart electrode materials with unattainable structure that cannot be achieved by traditional approaches, achieving eco-efficient conversion of pollutants into energy-storage nanomaterials, which will be a promising research field for interdisciplinary of energy, biology, and environment.

KOH-activated hollow carbon spheres with surface functionalization for high-capacity and long-cycle-life lithium-selenium batteries

Lithium-selenium (Li-Se) batteries are considered promising alternatives to lithium-ion batteries due to their higher volumetric capacity and energy density. However, they still face limitations in efficiently utilizing the active selenium. Here, we develop surface-functionalized mesoporous hollow carbon nanospheres as the selenium host. By using KOH activation, the surface of the carbon nanospheres is functionalized with hydroxyl groups, which greatly improve the utilization of selenium and facilitate the conversion of lithium selenides, leading to much higher capacities compared to ZnCl2 activation and untreated carbon nanospheres. Theory and experimental evidence suggest that surface hydroxyl groups can enhance the reduction conversion of polyselenides to selenides and facilitate the oxidation reaction of selenides to elemental selenium. In-situ and ex-situ characterization techniques provided additional confirmation of the hydroxyl groups electrochemical durability in catalyzing selenium conversion. The meticulously engineered Se cathode demonstrates a high specific capacity of 594 mA h g−1 at 0.5C, excellent rate capability of 464 mA h g−1 at 2C, and a stable cycling performance of 500 cycles at 2C with a capacity retention of 84.8 %, corresponding to an ultra-low-capacity decay rate of 0.0144 % per cycle, surpassing many reported lithium-selenium battery technologies.

Tailoring Versatile Cathodes and Induced Anodes for Zn-Se Batteries: Anisotropic Orientation of Tin-Based Materials within Bowl-In-Ball Carbon.

The advancement of Zn-Se batteries has been hindered by significant challenges, such as the sluggish kinetics of Se cathodes, limited Se loading, and uncontrollable formation of Zn dendrites. In this study, a bidirectional optimization strategy is devised for both cathode and anode to bolster the performance of Zn-Se batteries. A novel bowl-in-ball structured carbon (BIBCs) material is synthesized to serve as a nanoreactor, in which tin-based materials are grown and derived in situ to construct cathodes and anodes. Within the cathode, the multifunctional host material (SnSe@BIBCs) exhibits large adsorption capacity for selenium, and demonstrates supreme catalytic properties and spatially confined characteristics toward the selenium reduction reaction (SeRR). On the anode, Sn@BIBCs displays triple-induced properties, including the zincophilic of the internal metallic Sn, the homogenized spatial electric field from the 3D spatial structure, and the curvature effect of the bowl-shaped carbon. Collectively, these factors induce preferential nucleation of Zn, ensuring its uniform deposition. As a result, the integrated Zn-Se battery system achieves a remarkable specific capacity of up to 603 mAh g-1 and an impressive energy density of 581W kg-1, highlighting its tremendous potential for practical applications.

In-situ texturing hollow carbon host anchored with Fe single atoms accelerating solid-phase redox for Li-Se batteries

Se-based cathodes have caught tremendous attention owing to their comparable volumetric capacity and better electronic conductivity to S cathodes. However, its low utilization ratio and sluggish redox kinetics due to the high reaction barrier of solid-phase transformation from Se to Li2Se limit its practical application. Herein, an in-situ texturing hollow carbon host by gas–solid interface reaction anchored with Fe single-atomic catalyst is designed and prepared for advanced Li-Se batteries. This Se host presents high pore volume of 1.49 cm3 g−1, Fe single atom content of 1.53 wt%, and its specific structure protects single-atomic catalyst from the destructive reaction environment, thus balancing catalytic activity and durability. After Se loading by reduction of H2SeO3, this homogenous Se-based cathode delivers a superior rate capacity of 431.3 mA h g−1 at 4C, and great discharge capacity of 301.8 mA h g−1 after 1000 cycles at 10C, with high Li-ion diffusion coefficient and capacitance-contributed ratio. The distribution of relaxation times analysis verifies solid-phase transformation mechanism of this cathode and density functional theory calculations confirm the adsorption and bidirectionally catalysis effect of Fe single-atomic catalyst. This work provides a new strategy to prepare high-efficient Se cathode associated with non-noble metal single atoms for high-performance Li-Se batteries.

In-situ confining selenium within bubble - like carbon nanoshells for ultra-stable Li-Se batteries.

Lithium-selenium (Li-Se) batteries are promising energy storage devices. However, the long-term durability and high-rate performance of the Se cathode have been limited by significant volume expansion and the troublesome shuttle effect of polyselenides during repeated charging/discharging processes. To revolutionize these issues, we applied a top-down strategy through the in-situ trapping of amorphous Se within bubble-like carbon (BLC) frameworks, which can radically minimize the presence of surface-absorbed Se while enhancing Se loading capacity. This ingenious technique successfully encapsulates all Se species within carbon nanoshells, creating a distinct half-filled core-shell structure known as Se@void@BLC. This in-situ trapping approach ensures the efficient management of Se volume changes during repeated discharge and charge cycles. Moreover, an extraordinary Se loading capacity of up to 65.6 wt% is reached. Using the Se@void@BLC as cathode for Li-Se battery, we achieve a high initial Columbic efficiency of 84.2 %, a high reversible capacity of 585 mAh g-1 , and an ultralow capacity decay of only 0.0037 % per cycle during 4000 cycles at 10 A g-1 .

High performance all-solid-state Li–Se battery based on selenium loaded on Ti3C2 MXene cathode

Selenium has high theoretical volumetric capacity of 3253 mAh cm−3 and acceptable electronic conductivity of 1 × 10−5 S m−1, which is considered as a potential alternative to sulfur cathode for all-solid-state rechargeable batteries with high energy density. However, the development of all-solid-state Li–Se batteries (ASSLSBs) are hindered by sluggish kinetics and poor cycling life. In this work, trigonal Se nanocrystallines are homogenously distributed in the interspace and on the surface of MXene layers (denoted as Se@MXene composite) by a novel melt-diffusion method. ASSLSBs based on this Se@MXene composite cathode exhibit large specific capacity of 632 mAh g−1 at 0.05 A g−1, high-rate capability over 4 A g−1, and excellent cycling stability over 300 cycles at 1 A g−1. The ex-situ analytical techniques demonstrate that the excellent electrochemical performance of Se@MXene cathode largely arises from structural stability with the assistance of conductive MXene and reversible redox behavior between Li2Se and Se during the repeating charge/discharge process. Our study points out the potential of material design of Se cathode based on conducting 2D materials with good electrochemical behavior, which may accelerate the practicability of ASSLSBs.

Natural okra gum as functional binder enables highly stable Lithium–Selenium batteries

Lithium–selenium (Li–Se) batteries are garnered significant attention due to their high theoretical specific capacity, high volumetric energy density and moderate output voltage. Nevertheless, Li–Se batteries are still restricted by severe volume expansion and “shuttle effect” of polyselenides, resulting in deteriorated electrochemical performance. Binders are a crucial component of Li–Se batteries, playing a key role in addressing the mentioned issues. Herein, a non-toxic, bio-friendly, hydro-soluble binder of okra gum (OG) extracted from okra pods is proposed to ameliorate the electrochemical performance of Li–Se batteries. The as-prepared OG binders are rich in branched-chain polysaccharides (glucoside) and polar functional groups (–C–O–C–, –COOH), which not only have a good interpenetrating binding network to ensure the mechanical stability of Se cathode, but also have excellent interfacial chemical binding force for immobilizing polyselenides. Consequently, the OG binder endows Li–Se batteries with high initial discharge capacity (607 mA h g−1 at 0.2C), good cycling stability (218 mA h g−1 after 100 cycles at 0.2C), and remarkable rate performance (364 mA h g−1 at 1C), all of which are superior to Li–Se batteries with PVDF binder. Our study demonstrates the feasibility of natural mucilage as functional binder for Li–Se batteries and paves a research path in developing natural plant-based binders to stabilize electrode materials for reliable high-energy batteries.

A review of all‐solid‐state lithium‐selenium batteries

AbstractRechargeable lithium‐selenium batteries (LSeBs) are promising candidates for next‐generation energy storage systems due to their exceptional theoretical volumetric energy density (3253 mAh cm−3). However, akin to lithium‐sulfur batteries, the adoption of LSeBs has been hampered by problems such as polyselenides migration in liquid electrolytes, uncontrolled dendrite growth and safety concerns. To overcome these issues, researchers proposed to use the solid‐state electrolytes (SSEs) as a method, which could mitigate the formation of polyselenides. However, practical utilization of the all‐solid‐state Li‐Se batteries (ASSLSeBs) face significant obstacles, including sluggish redox kinetics during Se conversion (Se ↔ Li2Se), inadequate interfacial contact and formation of Li dendrites. Scientists have applied strategies to tackle these challenges. This article offers a timely review of emerging strategies. The article begins by conducting a detailed analysis of the working principles of ASSLSeBs and identifying the critical challenges that hinder practical application. Subsequently, the article presents a comprehensive summary of various strategies aimed at boosting the development of ASSLSeBs, which encompass advancements in Se cathode materials, optimization of SSEs, design of stable Li anodes, and approaches in addressing the interfacial challenge. Finally, the article offers further perspectives about promoting the application of ASSLSeBs. It highlights the need for continued research and development to overcome existing limitations. Overall, by understanding these emerging strategies, researchers could enhance the technology of LSeBs, bringing us closer to the practical realization of high‐energy storage systems.

High-performance lithium–selenium batteries enabled by nitrogen-doped porous carbon from peanut meal

Abstract Biomass-derived porous carbon displays a great potential for lithium–selenium (Li–Se) batteries owing to its green resource and inherent structural advantages, which can effectively restrict the shuttle effect of Se cathode. Peanut meal, by-product of the extraction of peanut oil, is a promising precursor for N-doped porous carbon. However, peanut meal is difficult to be activated in solution due to its high hydrophobicity. Thus, non-reports have been available for peanut meal-derived porous carbon used as Li–Se battery cathode host. In this work, we have innovatively proposed a very simple method of activating peanut meal by directly physically grinding the activator with the peanut meal and then annealing it to convert it into nitrogen-doped three-dimensional porous carbon (N-PC) with rich nanoscale pore size structures, which is then used as the Se host for Li–Se batteries. The N-PC shows a high specific surface area of 938.872 m2 g−1. The Se/N-PC composite cathode delivers a specific capacity of 461.4 mA h g−1 for 250 cycles at 0.2 C, corresponding to a high-capacity retention of 97.2%. Moreover, the Se/N-PC composite maintains a high capacity over 340.1 mA h g−1 after 1,000 cycles at a high current density of 2 C. Our work effectively resolves the hydrophobic biomass activation problem and manufactures abundant and low-cost Se host for Li–Se batteries.

Activating Selenium Cathode Chemistry for Aqueous Zinc-Ion Batteries.

Aqueous rechargeable zinc-ion batteries (ARZIBs) are a promising next-generation energy storage device by virtue of the superior safety and low cost of both the aqueous electrolyte and zinc metal anode. However, their development has been hindered by the lack of suitable cathodes with high volumetric capacity that can provide both lightweight and compact size. Herein we report a novel cathode chemistry based on amorphous Se doped with transition metal Ru that mitigates the resistive surface layer produced by the side reactions between the Se cathode and aqueous electrolyte. This improvement can permit high volumetric capacity in this system. Distinct from conventional conversion mechanisms between Se and ZnSe in Se||Zn cells, this strategy realizes synchronous proton and Zn2+ intercalation/deintercalation in the Ru-doped amorphous Se||Zn half cells. Moreover, an unanticipated Zn2+ deposition/stripping process in this system further contributes to the superior electrochemical performance of this new cathode chemistry. Consequently, the Ru-doped amorphous Se||Zn half cells are found to deliver a record-high capacity of 721 mAh g-1 /3472 mAh cm-3 , and superior cycling stability of over 800 cycles with only 0.015% capacity decay per cycle. This reported work opens the door for new chemistries that can further improve the gravimetric and volumetric capacity of ARZIBs. This article is protected by copyright. All rights reserved.

Triggering Mixed Cationic‐Anionic Redox in Cu2‐xSe Cathodes via Tailored Charge‐Carrier for High Energy Density Aqueous Zn Batteries

AbstractThe further application of promising transition‐metal chalcogenides (TMCs) cathodes in dilute neutral aqueous Zn batteries (AZBs) is mainly plagued by unsatisfactory working voltages (usually <1 V vs Zn2+/Zn) and their conventional cationic redox centers reaching theoretical capacity limit. Hence, to break the confinement, a novel Zn‐Cu2‐xSe battery is developed in dilute neutral‐aqueous electrolyte by introducing a tailored charge‐carrier, which not only alters the intercalation potential of ions embedded into Cu2‐xSe (vs Zn2+/Zn, working voltage from ≈0.4 to ≈1.2 V) but also activates the anionic redox centers of Cu2‐xSe (capacity release from 143.4 to 323.2 mAh g−1 at 0.4 A g−1). In situ synchrotron X‐ray diffraction (SXRD) and substantial ex situ characterizations reveal the multi‐step phase conversion undergone by cathode and triggered additional Se‐based anionic (Sen2−/Se2−) reversible redox reaction. A multi‐electron synergistic transfer process established on the cationic‐anionic redox centers circumvents the slow relaxation of single‐ion charge compensation achieving high‐capacity and enhanced ion diffusion kinetics. As a result, an extraordinary energy density of up to 406.2 Wh kg−1 at 240 W kg−1 is implemented (calculated based on the mass of Cu2‐xSe cathode), which is ≈8.4 times higher than that of conventional Zn‐Cu2‐xSe batteries, representing an advanced development toward energetic AZBs.

Multiphysics factor facilitating fast reaction kinetics for high-power-density Li–Se batteries

An intriguing multiphysics factor for facilitating fast reaction kinetics is proposed herein to achieve high-power-density cathodes for lithium-selenium batteries (LSeBs) based on Se and Te-doped cathode models from the perspective of thermodynamic, chemical, and Li kinetics. Compared with the bare electrode, the optimized Te–Se electrode showed a much greater rate capability under harsh conditions in balancing the theoretical capacity and improving the redox kinetics. This fast kinetic property is understood in detail by cyclic voltammetry analysis, and a reduction in the electrochemical polarization, depending on the increase in the scan rate, is observed for the Te–Se electrode. In addition, the voltage hysteresis of the Se cathode increased rapidly in the C-rate mode, whereas that of the Te–Se electrode increased at a much slower rate. Therefore, a comparison of intrinsic thermodynamic hysteresis is performed to highlight the difference between the Se-based electrodes, and the reaction resistance and Li diffusion coefficient for the Te–Se cathode from the kinetic point of view are found to exhibit a superior feature during (dis)charging. The theoretical results are broken down into three perspectives: i) thermodynamics, ii) electronic structure, and iii) Li kinetics, systematically elucidating the fast kinetics of the Te-doped Se cathode compared to the pristine material. Lowering the formation energy, increasing the electronic population, and loosening the cation–anion bond are simultaneously triggered by Te doping, and their combined effects are deemed to be a multiphysics factor. The concrete experiment and computational understanding confirm the high power density of the Te–Se electrode relative to the reference model upon long-term cycling, and validate that the multiphysics factors pose a potentially global design strategy to enable fast kinetics for achieving high-performance LSeBs, even lithium-sulfur batteries.

Screening and activating small-molecule Se in microporous S-decorated/N-doped carbon spheres for an enhanced rate performance

Breaking the Sen into short chains and accelerating the phase transformation kinetics are of fundamental importance in achieving high-performance Se cathodes. However, challenges remain in the unraveled function of the microporosity and strategy to increase the affinity of the host material towards active Sen species. Herein, S-decorated N-doped carbon spheres with a range of micropores are prepared to regulate different sized short-chain Sen. Combined with the density functional theory (DFT) simulation on the geometry of Sen (2 ≤ n ≤ 8) small molecules, different micropores of the host in screening Sen (2 ≤ n ≤ 8) with higher activity, accelerated kinetics and optimized performance are elaborated. The sulfur molecules decoration provides abundant polar sites to enhance the chemisorption of both Sen and Li2Se and thus boosting the redox kinetics and Sen utilization rate of the Li-Se battery. The obtained S@NPC/Se-7 cathode displays an extraordinary rate capability (430.4 mAh g−1 at 5 C) and maintains an ultrastable cycling property (at 1 C over 500 cycles).

Controllable synthesis of vanadium-doped nickel-chalcogenide/graphene cathodes and MnV2O6·2H2O/graphene anode for high-energy asymmetric supercapacitors

Exploring novel electrode materials with rational morphology and structure is crucial for the fabrication of high-performance supercapacitors. In this work, novel vanadium-doped nickel-chalcogenide/reduced graphene oxide cathodes (NiV-S/rGO and NiV-Se/rGO) and MnV2O6·2H2O/rGO anode are controllably prepared through a facile solvothermal method. Benefiting from the two-dimensional structure and desirable surface electronic environment, the graphene-supported NiV-X/rGO (X = S and Se) cathodes exhibit outstanding capacitive performance (1734.2 and 1577.2C·g−1 at 2 A·g−1), remarkable cycling stability and exceptional rate performance. Meanwhile, with the encapsulation of graphene protect layers, the MnV2O6·2H2O/rGO anode also shows a significantly enhanced specific capacity and superb cycling stability (95.8 % retention after 10,000 cycles). When assembled into asymmetric supercapacitors, the NiV-S/rGO//MnV2O6·2H2O/rGO and NiV-Se/rGO//MnV2O6·2H2O/rGO devices not only exhibit ultra-high energy densities (82.4 and 60.0 Wh·kg−1 at a power density of 800.0 W·kg−1), but also display superior cycling stabilities (91.5 % and 93.7 % retention after 10,000 cycles). These excellent properties demonstrate their potential application prospect in supercapacitor with high energy densities.

Real-Time Visualizing Nucleation and Growth of Electrodes for Post-Lithium-Ion Batteries.

ConspectusUntil recently, most studies on nucleation and growth mechanisms have employed electrochemical transient measurements, and numerous models have been established on various metal electrode elements. Contrary to the conventional tip-induced nucleation and growth model, a base-induced nucleation and growth mode was discovered not so long ago, which highlighted the importance of direct real-time observations such as visualization. As analysis techniques developed, diverse in situ/operando imaging methods have spurred the fundamental understanding of complex and dynamic battery electrochemistry. Experimental observations of alkali Li and Na metals are limited and difficult because their high reactivity makes not only the fabrication but also the analysis itself challenging. Na metal has high reactivity to electrolytes. Accordingly, it is difficult to visualize the Na deposition in real-time due to gas evolution and resolution limitation. Only a few studies have examined the Na deposition and dissolution reactions in operando. It is generally believed that the Mg anode is free from the dendrite growth of Mg metal, and Mg deposition preferentially occurs along the surface direction. However, whether the Mg anode always follows the dendrite-free growth has currently become a controversial topic and is being discussed and redefined based on real-time imaging analyses. In addition, a variety of morphological evolutions in the metal anodes are required to be systematically distinguished by key parameters. Real-time imaging analysis can directly confirm the solid-liquid-solid multiphase conversion reactions of S and Se cathodes. S and Se elements belong to the same chalcogen group, but their crystal structures and morphological changes significantly differ in each electrode during deposition and dissolution reactions. Therefore, it is necessitated to discuss the nucleation and growth behaviors by examining intrinsic properties of each element in chalcogen cathodes. Considering that a mechanistic understanding of the Se cathode is in its infancy, its nucleation and growth behaviors must be further explored through fundamental studies. In this Account, we aim to discuss the nucleation and growth behaviors of metal (Li, Na, and Mg) anodes and chalcogen (S and Se) cathodes. To elucidate their nucleation and growth mechanisms, we overview the morphological evolutions on the electrode surface and interface by in situ/operando visualizations. Our recent studies covering Li, Na, Mg, S, and Se electrodes verified by operando X-ray imaging are used as critical resources in understanding their nucleation and growth behaviors. Overall, with validation of the complex and dynamic nucleation and growth behaviors of metal and chalcogen electrodes by in situ/operando visualization methods, we hope that this Account can contribute to supporting the fundamental knowledge for the development of high-energy-density metal and chalcogen electrodes.

Aqueous Zinc–Chalcogen Batteries: Emerging Conversion-Type Energy Storage Systems

Aqueous zinc (Zn) metal batteries are considered competitive candidates for next-generation energy storage, attributed to the abundance, low redox potential, and high theoretical capacity of Zn. However, conventional cathode materials are mainly based on ion-insertion electrochemistry, which can only deliver limited capacity. The conversion-type aqueous zinc–chalcogen batteries (AZCBs) have received widespread attention because they combine the advantages of chalcogen cathodes (S, Se, and Te) and Zn anodes to significantly enhance their capacity. Research on AZCBs has increased continuously; however, it is still in its infancy because the selection and regulation of cathode material systems are not comprehensive and systematic, and the investigation of the mechanisms is not thorough. Herein, we present a detailed overview explaining the recent progress of AZCBs, providing comprehensive guidelines for further research. First, research based on S cathodes, which is the most studied system among AZCBs, is summarized. Second, research based on Se and Te cathodes is described. Research on these different systems is mainly focused on electrolyte modification and cathode optimization. In each section, various strategies are introduced, and the working mechanisms are also discussed. Finally, the challenges and prospects for the development of AZCBs are presented.

Advanced all-solid-state lithium-selenium batteries enabled by selenium-nitrogen doped hierarchic meso-microporous carbon nanospheres composite cathode

Selenium, an element belonging to the same group in the periodic table as sulfur, has a high electronic conductivity (1 × 10−5 S/cm) and a high volumetric energy density (3253 mAh/cm3), which is a prospective cathode material for high-energy all-solid-state rechargeable batteries. However, its wide use is hindered by large volume expansion and low utilization rate. In this work, Se-infused nitrogen-doped hierarchical meso-microporous carbon composites (Se/NHPC) are prepared by a melt-diffusion process. Amorphous Se is uniformly dispersed in meso-micropores of NHPC with a high mass loading of 81%. All-solid-state Li-Se batteries fabricated by using Se/NHPC as the cathode, a Li-In alloy as the anode, and Li6PS5Cl as the solid-state electrolyte, deliver a highly reversible capacity of 621 mAh/g (92% of theoretical capacity), a good rate capability and a high capacity retention value of 80.9% after 100 cycles. It is found that the capacity decay of Se cathode is mainly related to the interfacial degradation and the separation of Se from the carbon substrate, as suggested by the continuous increase of interfacial resistance and the structural transformation from amorphous Sen chains to Se8 rings initial discharge/charge cycle and then to the trigonally crystalline Se chains structure after the long-term cycles.

Encapsulating selenium into mesoporous carbon for high-performance aqueous Cu-Se battery

As an appealing cathode material for rechargeable batteries, selenium (Se) attracts much attention benefitting from its outstanding electronic conductivity and high volumetric specific capacity. Whereas, Se cathode generally suffers from large volume expansion and polyselenides shuttling, which seriously hamper the progress of Se-based batteries. To overcome these challenges, a novel aqueous Cu-Se battery is designed by employing Se encapsulated in ordered mesoporous carbon (Se/CMK-3) as cathode. Via X-ray diffraction and X-ray photoelectron spectroscopy, the reaction mechanism of the designed battery is verified as a four-electron conversion of Se ↔ CuSe ↔ Cu5Se4 ↔ Cu2Se. Benefiting from the synergistic effects of four-electron conversion (Se ↔ Se2−, Cu2+↔Cu+) and robust mesoporous carbon host, the battery manifests high specific capacity (1009.5 mAh/g at 0.2 A/g) and favorable long-span cycling capability (93.7 % capacity retention after 400 cycles at 4.0 A/g). Therefore, this work provides a novel route for building high-performance aqueous Se-based batteries.

Cryo-EM Revealing the Origin of Excessive Capacity of the Se Cathode in Sulfide-Based All-Solid-State Li-Se Batteries.

Selenium (Se), whose electronic conductivity is nearly 25 orders higher than that of sulfur (S) and whose theoretical volumetric capacity is 3254 mAh cm-3, is considered as a potential alternative to S to overcome the poor electronic conductivity issue of the S cathode in the lithium (Li)-S battery. However, the study of the Li-Se battery, particularly a Li-Se all-solid-state battery (ASSB), is still in its infancy. Herein, we report the performance of Li-Se ASSBs at both room temperature (RT) and high temperature (HT, 50 °C), using a Li10Si0.3PS6.9Cl1.8 (LSPSCl) solid-state electrolyte and Li-In anode. With a Se loading of 7.6 mg cm-2, the Li-Se battery displayed a record high reversible capacity of 6.8 mAh cm-2 after 50 cycles at HT, which exceeds the theoretical areal capacity of 5.2 mAh cm-2 for Se. Moreover, the RT Li-Se ASSB delivered an initial areal capacity of about 2 mAh cm-2 at a current density of 1 A g-1 for 1200 cycles with a capacity retention of 67%. Cryo-electron microscopy revealed that the excessive capacity of Se at HT can be attributed to the formation of a previously unknown S5Se4 phase during charging, which participated reversibly in a subsequent redox reaction. The formation of the S5Se4 phase originated from the reaction of Se with S, which was generated by the decomposition of LSPSCl at HT. These results unlock the electrochemistry of a Li-Se ASSB, suggesting that a Li-Se ASSB is a viable alternative to a Li-S battery for energy storage applications.