Urchin-Like Fe3 Se4 Hierarchitectures: A Novel Pseudocapacitive Sodium-Ion Storage Anode with Prominent Rate and Cycling Properties

Layered Na2Ti3O7 as an Ultrastable Intercalation-Type Anode for Non-Aqueous Calcium-Ion Batteries

Calcium ion batteries (CIBs) are a promising energy storage device due to the low redox potential of the Ca metal and the abundant reserves of the Ca element. However, the large radius and divalent nature of Ca2+ lead to its slow ion diffusion kinetics and the lack of suitable electrode materials for Ca storage. Here, a layered structure of Na2Ti3O7 (NTO) is presented as an anode material for nonaqueous CIBs. This NTO anode demonstrates a high discharge capacity of 165 mA h g-1 at 100 mA g-1 and a remarkable capacity retention rate of 80%, even after 2000 cycles at 500 mA g-1, surpassing the performance of all reported intercalation-type anode materials for CIBs. The NTO transfers to layered CaVIINaIXTi3O7 (CNTO) with intercalation of Ca2+ and extraction of Na+ during the first discharge process. Then, the CNTO undergoes the reversible insertion/extraction of Ca2+ during subsequent cycling. Additionally, density functional theory calculations reveal that NTO possesses a rapid two-dimensional diffusion pathway for Ca2+. Moreover, the full CIBs based on NTO as the anode further underscore its potential for CIBs. This work presents promising anode materials for CIBs, offering opportunities to promote the development of high-performance CIBs.

Deciphering the Performance Enhancement, Cell Failure Mechanism, and Amelioration Strategy of Sodium Storage in Metal Chalcogenides-Based Andes

Transition metal chalcogenides (TMCs) emerge as promising anode materials for sodium-ion batteries (SIBs), heralding a new era of energy storage solutions. Despite their potential, the mechanisms underlying their performance enhancement and susceptibility to failure in ether-based electrolytes remain elusive. This study delves into these aspects, employing CoS2 electrodes as a case in point to elucidate the phenomena. The investigation reveals that CoS2 undergoes a unique irreversible and progressive solid-liquid-solid phase transition from its native state to sodium polysulfides (NaPSs), and ultimately to a Cu1.8S/Co composite, accompanied by a gradual morphological transformation from microspheres to a stable 3D porous architecture. This reconstructed 3D porous structure is pivotal for its exceptional Na+ diffusion kinetics and resilience to cycling-induced stress, being the main reason for ultrastable cycling and ultrahigh rate capability. Nonetheless, the CoS2 electrode suffers from an inevitable cycle life termination due to the microshort-circuit induced by Na metal corrosion and separator degradation. Through a comparative analysis of various TMCs, a predictive framework linking electrode longevity is established to electrode potential and Gibbs free energy. Finally, the cell failure issue is significantly mitigated at a material level (graphene encapsulation) and cell level (polypropylene membrane incorporation) by alleviating the NaPSs shuttling and microshort-circuit.

Crab Shell-Derived SnS2/C and FeS2/C Carbon Composites as Anodes for High-Performance Sodium-Ion Batteries

The demand for energy storage devices has increased significantly, and the sustainable development of lithium-ion batteries is limited by scarce lithium resources. Therefore, alternative sodium-ion batteries which are rich in resource may become more competitive in the future market. In this work, we synthesized low-cost SnS₂/C and FeS₂/C anode materials of sodium-ion batteries which used waste crab shells as biomass carbon precursor. The SnS₂ nanosheet and FeS₂ nanosphere structures are deposited on the crab shell-derived carbon through simple hydrothermal reaction. Due to the coexistence of transition metal dichalcogenides (TMDs) and crab-derived biomass carbon, the anode material has excellent cycle stability and rate performance. SnS₂/C and FeS₂/C deliver capacities of 535.4 and 479 mA h g^-1 at the current density of 0.1 A g^-1, respectively. This study explored an effective and economical strategy to use biomass and TMDs to construct high-performance sodium-ion batteries.

Interfacial Coupling SnSe2 /SnSe Heterostructures as Long Cyclic Anodes of Lithium-Ion Battery

Tin selenide (SnSe₂ ) is considered a promising anode of the lithium-ion battery because of its tunable interlayer space, abundant active sites, and high theoretical capacity. However, the low electronic conductivity and large volume variation during the charging/discharging processes inevitably result in inadequate specific capacity and inferior cyclic stability. Herein, a high-throughput wet chemical method to synthesize SnSe₂ /SnSe heterostructures is designed and used as anodes of lithium-ion batteries. The hierarchical nanoflower morphology of such heterostructures buffers the volume expansion, while the built-in electric field and metallic feature increase the charge transport capability. As expected, the superb specific capacity (≈911.4 mAh g^-1 at 0.1 A g^-1 ), high-rate performance, and outstanding cyclic stability are obtained in the lithium-ion batteries composed of SnSe₂ /SnSe anodes. More intriguingly, a reversible specific capacity (≈374.7 mAh g^-1 at 2.5 A g^-1 ) is maintained after 1000 cycles. The internal lithium storage mechanism is clarified by density functional theory (DFT) calculations and in situ characterizations. This work hereby provides a new paradigm for enhancing lithium-ion battery performances by constructing heterostructures.

Metal Selenides Anode Materials for Sodium Ion Batteries: Synthesis, Modification, and Application

The powerful and rapid development of lithium-ion batteries (LIBs) in secondary batteries field makes lithium resources in short supply, leading to rising battery costs. Under the circumstances, sodium-ion batteries (SIBs) with low cost, inexhaustible sodium reserves, and analogous work principle to LIBs, have evolved as one of the most anticipated candidates for large-scale energy storage devices. Thereinto, the applicable electrode is a core element for the smooth development of SIBs. Among various anode materials, metal selenides (MSe_x ) with relatively high theoretical capacity and unique structures have aroused extensive interest. Regrettably, MSe_x suffers from large volume expansion and unwished side reactions, which result in poor electrochemistry performance. Thus, strategies such as carbon modification, structural design, voltage control as well as electrolyte and binder optimization are adopted to alleviate these issues. In this review, the synthesis methods and main reaction mechanisms of MSe_x are systematically summarized. Meanwhile, the major challenges of MSe_x and the corresponding available strategies are proposed. Furthermore, the recent research progress on layered and nonlayered MSe_x for application in SIBs is presented and discussed in detail. Finally, the future development focuses of MSe_x in the field of rechargeable ion batteries are highlighted.

Thermodynamic Transformation of Crystalline Organic Hybrid Iron Selenide to FexSey@CN Microrods for Sodium Ion Storage

Carbon-coated metal chalcogenide composites have been demonstrated as one type of promising anode material for sodium-ion batteries (SIBs). However, combining carbon materials with micronanoparticles of metal chalcogenide always involve complicated processes, such as polymer coating, carbonization, and sulfidation/selenization. To address this issue, herein, we reported a series of carbon-coated FexSey@CN (FexSey = FeSe2, Fe3Se4, Fe7Se8) composites prepared via the thermodynamic transformation of a crystalline organic hybrid iron selenide [Fe(phen)2](Se4) (phen = 1,10-phenanthroline). By pyrolyzing the bulk crystals of [Fe(phen)2](Se4) at different temperatures, FexSey microrods were formed in situ, where the nitrogen-doped carbon layers were coated on the surface of the microrods. Moreover, all the as-prepared FexSey@CN composites exhibited excellent sodium-ion storage capabilities as anode materials in SIBs. This work proves that crystalline organic hybrid metal chalcogenides can be used as a novel material system for the in situ formation of carbon-coated metal chalcogenide composites, which could have great potential in the application of electrochemical energy storage.

Boosting Charge Transfer Via Heterostructure Engineering of Ti2 CTx /Na2 Ti3 O7 Nanobelts Array for Superior Sodium Storage Performance

The poor conductivity, inert charge transmission efficiency, and irreversible Na⁺ trapping of Na₂ Ti₃ O₇ result in retardant electrons/ions transportation and deficient sodium-ion storage efficiency, leading to sluggish reaction kinetics. To address these issues, an urchin-like Ti₂ CT_x /Na₂ Ti₃ O₇ (Ti₂ C/NTO) heterostructure sphere consisting of Ti₂ C/NTO heterostructure nanobelts array is developed via a facile one-step in situ hydrothermal strategy. The Ti₂ C/NTO heterostructure can obviously decrease Na⁺ diffusion barriers and increase electronic conductivity to improve reaction kinetics due to the built-in electric field effect and high-quantity interface region. In addition, the urchin-like vertically aligned nanobelts can reduce the diffusion distance of electrons and ions, provide favored electrolyte infiltration, adapt large volume expansion, and mitigate the aggregation to maintain structural stability during cycles, further enhancing the reaction kinetics. Furthermore, the Ti₂ C/NTO heterostructure can effectively suppress many unwanted side reactions between reactive surface sites of NTO and electrolyte as well as irreversible trapping of Na⁺ . As a result, systematic electrochemical investigations demonstrate that the Ti₂ C/NTO heterostructure as an anode material for record sodium-ion storage delivers the highest reversible capacity, the best cycling stability with 0.0065% decay rate for 4500 cycles at 2.0 A g^-1 , and excellent rate capability of 172.1 mAh g^-1 at 10.0 A g^-1 .

In-situ fabrication of active interfaces towards FeSe as advanced performance anode for sodium-ion batteries

Transition metal selenides have gained enormous interest as anodes for sodium ion batteries (SIBs). Nonetheless, their large volume expansion causing poor rate and inferior cycle stability during Na⁺ insertion/extraction process hinders their further applications in SIBs. Herein, a confined-regulated interfacial engineering strategy towards the synthesis of FeSe microparticles coated by ultrathin nitrogen-doped carbon (NC) is demonstrated (FeSe@NC). The strong interfacial interaction between FeSeand NC endows FeSe@NC with fast electron/Na⁺ transport kinetics and outstanding structural stability, delivering unexceptionable rate capability (364 mAh/gat 10 A/g) and preeminent cycling durability (capacity retention of 100 % at 1 A/g over 1000 cycles). Furthermore, variousex situcharacterization techniques and density functional theory (DFT) calculations have been applied to demonstrate the Na⁺ storage mechanism of FeSe@NC. The assembled Na₃V₂(PO₄)₂F₃@rGO//FeSe@NC full cell also displays a high capacity of 241 mAh/gat 1 A/g with the capacity retention of nearly 100 % over 2000 cycles, and delivers a supreme energy density of 135 Wh kg^-1 and a topmost power density of 495 W kg^-1, manifesting the latent applications of FeSe@NC in the fast charging SIBs.

Bimetallic Sulfide SnS2/FeS2 Nanosheets as High-Performance Anode Materials for Sodium-Ion Batteries

Transition-metal sulfide SnS₂ has aroused wide concern due to its high capacity and nanosheet structure, making it an attractive choice as the anode material in sodium-ion batteries. However, the large volume expansion and poor conductivity of SnS₂ lead to inferior cycle stability as well as rate performance. In this work, FeS₂ was in situ introduced to synchronously grow with SnS₂ on rGO to prepare a heterojunction bimetallic sulfide nanosheet SnS₂/FeS₂/rGO composite. The composition and distinctive structure facilitate the rapid diffusion of Na⁺ and improve the charge transfer at the heterogeneous interface, providing sufficient space for volume expansion and improving anode materials' structural stability. SnS₂/FeS₂/rGO bimetallic sulfide electrode boasts a capacity of 768.3 mA h g^-1 at the current density of 0.1 A g^-1, and 541.2 mA h g^-1 at the current density of 1 A g^-1 in sodium-ion batteries, which is superior to that of either single metal sulfide SnS₂ or FeS₂. TDOS calculation further confirms that the binding of FeS₂/SnS₂-Na is more stable than FeS₂ and SnS₂ alone. The superior electrochemical performance of the SnS₂/FeS₂/rGO composite material makes it a promising candidate for sodium storage.

Fe7Se8 encapsulated in N-doped carbon nanofibers as a stable anode material for sodium ion batteries

Transition metal chalcogenides especially Fe-based selenides for sodium storage have the advantages of high electric conductivity, low cost, abundant active sites, and high theoretical capacity. Herein, we proposed a facile synthesis of Fe₇Se₈ embedded in carbon nanofibers (denoted as Fe₇Se₈-NCFs). The Fe₇Se₈-NCFs with a 1D electron transfer network can facilitate Na⁺ transportation to ensure fast reaction kinetics. Moreover, Fe₇Se₈ encapsulated in carbon nanofibers, Fe₇Se₈-NCFs, can effectively adapt the volume variation to keep structural integrity during a continuous Na⁺ insertion and extraction process. As a result, Fe₇Se₈-NCFs present improved rate performance and remarkable cycling stability for sodium storage. The Fe₇Se₈-NCFs exhibit practical feasibility with a reasonable specific capacity of 109 mA h g^-1 after 200 cycles and a favorable rate capability of 136 mA h g^-1 at a high rate of 2 A g^-1 when coupled with Na₃V₂(PO₄)₃ to assemble full sodium ion batteries.

Anchoring SnS2 on TiC/C Backbone to Promote Sodium Ion Storage by Phosphate Ion Doping

Tin disulfide (SnS₂ ) shows promising properties toward sodium ion storage with high capacity, but its cycle life and high rate capability are still undermined as a result of poor reaction kinetics and unstable structure. In this work, phosphate ion (PO₄ ^3- )-doped SnS₂ (P-SnS₂ ) nanoflake arrays on conductive TiC/C backbone are reported to form high-quality P-SnS₂ @TiC/C arrays via a hydrothermal-chemical vapor deposition method. By virtue of the synergistic effect between PO₄ ^3- doping and conductive network of TiC/C arrays, enhanced electronic conductivity and enlarged interlayer spacing are realized in the designed P-SnS₂ @TiC/C arrays. Moreover, the introduced PO₄ ^3- can result in favorable intercalation/deintercalation of Na⁺ and accelerate electrochemical reaction kinetics. Notably, lower bandgap and enhanced electronic conductivity owing to the introduction of PO₄ ^3- are demonstrated by density function theory calculations and UV-visible absorption spectra. In view of these positive factors above, the P-SnS₂ @TiC/C electrode delivers a high capacity of 1293.5 mAh g^-1 at 0.1 A g^-1 and exhibits good rate capability (476.7 mAh g^-1 at 5 A g^-1 ), much better than the SnS₂ @TiC/C counterpart. This work may trigger new enthusiasm on construction of advanced metal sulfide electrodes for application in rechargeable alkali ion batteries.