Fundamental Understanding on Selenium Electrochemistry:From Electrolytic Cell to Advanced Energy Storage

Selenium(Se),as an important quasi-metal element,has attracted much attention in the fields of thin-film solar cells,electrocatalysts and energy storage applications,due to its unique physical and chemical properties.However,the electrochemical behavior of Se in different systems from electrolytic cell to battery are complex and not fully understood.In this article,we focus on the electrochemical processes of Se in aqueous solutions,molten salts and ionic liquid electrolytes,as well as the application of Se-containing materials in energy storage.Initially,the electrochemical behaviors of Se-containing species in different systems are comprehensively summarized to understand the complexity of the kinetic processes and guide the Se electrodeposition.Then,the relationship between the deposition conditions and resulting structure and morphology of electrodeposited Se is discussed,so as to regulate the morphology and composition of the products.Finally,the advanced energy storage applications of Se in thin-film solar cells and secondary batteries are reviewed,and the electrochemical reaction processes of Se are systematically comprehended in monovalent and multivalent metal-ion batteries.Based on understanding the fundamental electrochemistry mechanism,the future development directions of Se-containing materials are considered in view of the in-depth review of reaction kinetics and energy storage applications.

Core-shell mesoporous carbon hollow spheres as Se hosts for advanced Al-Se batteries

Incorporating a selenium(Se)positive electrode into aluminum(Al)-ion batteries is an effective strategy for improving the overall battery performance.However,the cycling stability of Se positive electrodes has challenges due to the dissolution of intermediate reaction products.In this work,we aim to harness the advantages of Se while reducing its limitations by preparing a core-shell mesoporous carbon hollow sphere with a titanium nitride(C@TiN)host to load 63.9wt%Se as the positive electrode material for Al-Se batteries.Using the physical and chemical confinement offered by the hollow mesoporous carbon and TiN,the obtained core-shell mesoporous carbon hollow spheres coated with Se(Se@C@TiN)display superior utilization of the active material and remarkable cycling stability.As a result,Al-Se batteries equipped with the as-prepared Se@C@TiN composite positive electrodes show an initial discharge specific capacity of 377 mAh·g^(-1)at a current density of 1000 mA·g^(-1)while maintaining a discharge specific capacity of 86.0 mAh·g^(-1)over 200 cycles.This improved cycling performance is ascribed to the high electrical conductivity of the core-shell mesoporous carbon hollow spheres and the unique three-dimensional hierarchical architecture of Se@C@TiN.

3D skeleton nanostructured Ni_3S_2/Ni foam@RGO composite anode for high-performance dual-ion battery

The growing global demands of safe, low-cost and high working voltage energy storage devices trigger strong interests in novel battery concepts beyond state-of-art lithium-ion battery. Herein, a dualion battery based on nanostructured Ni_3S_2/Ni foam@RGO(NSNR) composite anode is developed, utilizing graphite as cathode material and LiPF6-VC-based solvent as electrolyte. The battery operates at high working voltage of 4.2–4.5 V, with superior discharge capacity of ～90 m A h g^(-1) at 100 mA g^(-1), outstanding rate performance, and long-term cycling stability over 500 cycles with discharge capacity retention of ～85.6%. Moreover, the composite simultaneously acts as the anode material and the current collector, and the corrosion phenomenon can be greatly reduced compared to metallic Al anode. Thus, this work represents a significant step forward for practical safe, low-cost and high working voltage dual-ion batteries,showing attractive potential for future energy storage application.

MOF-based quasi-solid-state electrolyte for long-life Al-Se battery

Aluminum-selenium(Al-Se)batteries,which possess a high theoretical specific capacity of 1357 mA h g^(-1),represent a promising energy storage technology.However,they suffer from significant attenuation of capacity and low cycle life due to the shuttle effect.To mitigate the shuttle effect induced by soluble selenium chloroaluminate compound that tends to migrate towards the negative electrode,a quasi-solid-state Al-Se battery was fabricated through the synthesis of a multi-aperture structure quasisolid-state electrolyte(MOF@GPE)based on metal-organic framework(MOF)material and gel-polymer electrolyte(GPE).The high ionic conductivity(1.13×10^(-3)S cm^(-1))of MOF@GPE at room temperature,coupled with its wide electrochemical stability window(2.45 V),can facilitate ion transport kinetics and enhance the electrochemical performance of Al-Se batteries.The MOF@GPE-based quasi-solidstate Al-Se batteries exhibit outstanding long-life cycling stability,delivering a high specific discharge capacity of 548 mA h g^(-1)with a maintained discharge specific capacity of 345 mA h g^(-1)after 500 cycles at a current density of 200 mA g^(-1).The stable ion transmission and high ion transport kinetics in MOF@GPE can be attributed to the stable structure and permeable channel of MOF,which effectively captures the soluble selenium chloroaluminate compound and further restrains the shuttle effect,resulting in improved cycling performance.

Hierarchical N-doped porous carbon hosts for stabilizing tellurium in promoting Al-Te batteries

Aluminum batteries are attractive in electrochemical energy storage due to high energy density and lowcost aluminum,while the energy density is limited for the lack of favorable positive electrode materials to match aluminum negative electrodes.Tellurium positive electrode is intrinsically electrically conductive among chalcogen and holds high theoretical specific capacity(1260.27 mAh g^(-1)) and discharge voltage plateau(~1,5 V).However,the chemical and electrochemical dissolution of Te active materials results in the low material utilization and poor cycling stability.To enhance the electrochemical performance,herein a nitrogen doped porous carbon(N-PC) is derived from zeolite imidazolate framework(ZIF-67)as an effective tellurium host to suppress the undesired shuttle effect.In order to inhibit the volume expansion of N-PC during the charge/discharge process,the reduced graphene oxide(rGO) nanosheets are introduced to form a stable host materials(N-PC-rGO) for stabilizing Te.The physical encapsulation and chemical confinement to soluble tellurium species are achieved.N-PC-rGO-Te positive electrode exhibits an improved initial specific capacity and long-term cycling performance at a current density of 500 mA g^(-1)(initial specific capacity:935.5 mAh g^(-1);after 150 cycles:467.5 mAh g^(-1)), highlighting a promising design strategy for inhibiting chemical and electrochemical dissolution of Te.

An efficient molten-salt electro-deoxidation strategy enabling fast-kinetics and long-life aluminum-selenium batteries

Aluminum-selenium(Al-Se)batteries have been considered as one of the most promising energy storage systems owing to their high capacity,energy density,and cost effectiveness,but Se falls challenges in addressing the shuttle effect of soluble intermediate product and sluggish reaction kinetics in the solid-solid conversion process during cycling.Herein,we propose an unprecedented design concept for fabricating uniform Se/C hollow microspheres with controllable morphologies through low-temperature electro-deoxidation in neutral NaCl-AlCl_(3) molten salt system.Such Se/C hollow microspheres are demonstrated to hold a favorable hollow structure for hosting Se,which can not only suppress the dissolution of soluble intermediate products into the electrolyte,thereby maintaining the structural integrity and maximizing Se utilization of the active material,but also promote the electrical/ionic conductivity,thus facilitating the rapid reaction kinetics during cycling.Accordingly,the as-prepared Se/C hollow microspheres exhibit a high reversible capacity of 720.1 mAh g^(−1)at 500 mA g^(−1).Even at the high current density of 1000 mA g^(−1),Se/C delivers a high discharge capacity of 564.0 mAh g^(−1),long-term stability over 1100 cycles and high Coulombic efficiency of 98.6%.This present work provides valuable insights into short-process recovery of advanced Se-containingmaterials and value-added utilization for energy storage.

Al homogeneous deposition induced by N-containing functional groups for enhanced cycling stability of Al-ion battery negative electrode

Rechargeable Al-ion batteries(AIBs)are considered as one of the most fascinating energy storage systems due to abundant Al resource and low cost.However,the cycling stability is subjected to critical problems for using Al foil as negative electrode,including Al dendrites,corrosion and pulverization.For addressing these problems,here a lightweight self-supporting N-doped carbon rod array(NCRA)is demonstrated for a long-life negative electrode in AIBs.Experimental analysis and first-principle calculations reveal the storage mechanism involving the induced deposition of N-containing function groups to Al as well as the ideal skeleton of the NCRA matrix for Al plating/stripping,which is favorable for regulating Al nucleation and suppressing dendrites growth.Compared with the Al foil,the NCRA exhibits lower areal mass density(∼72%of Al foil),smaller thickness(40%of Al foil),but much longer cycle life(>4 times of Al foil).Benefiting from the remarkable stability of the array structure,symmetric cells show excellent cycling stability with small voltage hysteresis(∼80 mV)and meanwhile there are no corrosion and pulverization problems even after cycled for 120 hours.Besides,full cells also manifest long lifespan(1,500 cycles)and increased Coulombic efficiency(100±1%).