Spatial and Temporal Analysis of Sodium-Ion Batteries

Heterogeneous engineering and carbon confinement strategy to synergistically boost the sodium storage performance of transition metal selenides

Transition metal selenides (TMSs) stand out as a promising anode material for sodium-ion batteries (SIBs) owing to their natural resources and exceptional sodium storage capacity. Despite these advantages, their practical application faces challenges, such as poor electronic conductivity, sluggish reaction kinetics and severe agglomeration during electrochemical reactions, hindering their effective utilization. Herein, the dual-carbon-confined CoSe2/FeSe2@NC@C nanocubes with heterogeneous structure are synthesized using ZIF-67 as the template by ion exchange, resorcin-formaldehyde (RF) coating, and subsequent in situ carbonization and selenidation. The N-doped porous carbon promotes rapid electrolyte penetration and minimizes the agglomeration of active materials during charging and discharging, while the RF-derived carbon framework reduces the cycling stress and keeps the integrity of the material structure. More importantly, the built-in electric field at the heterogeneous boundary layer drives electron redistribution, optimizing the electronic structure and enhancing the reaction kinetics of the anode material. Based on this, the nanocubes of CoSe2/FeSe2@NC@C exhibits superb sodium storage performance, delivering a high discharge capacity of 512.6 mA h g-1 at 0.5 A g-1 after 150 cycles and giving a discharge capacity of 298.2 mA h g-1 at 10 A g-1 with a CE close to 100.0 % even after 1000 cycles. This study proposes a viable method to synthesize advanced anodes for SIBs by a synergy effect of heterogeneous interfacial engineering and a carbon confinement strategy.

Unraveling the modified mechanism of ruthenium substitution on Na3V2(PO4)3 with superior rate capability and ultralong cyclic performance

Na3V2(PO4)3(NVP) is an ideal cathode material for sodium ion battery due to its stable three-dimensional frame structure and high operating voltage. However, the low intrinsic conductivity and serious structural collapse limit its further application. In this work, a simultaneous optimized Na3V1.96Ru0.04(PO4)3/C@CNTs cathode material is synthesized by a simple sol-gel method. Specifically, the ionic radius of Ru3+ is slightly larger than that of V3+ (0.68 Å vs 0.64 Å), which not only ensures the feasibility of Ru3+ replacing V3+ site, but also appropriately expands the migration channel of sodium ions in NVP and stabilizes the structure, effectively improving the diffusion efficiency of sodium ions. Moreover, CNTs construct a three-dimensional conductive network between the grains, reducing the impedance at the interface and effectively improving the electronic conductivity. Ex-situ XRD analysis at different SOC were performed to determine the change in the crystal structure of Ru3+doped Na3V2(PO4)3, and the refinement results simultaneously demonstrate the relatively low volume shrinkage value of less than 3 % during the de-intercalation process, further verifying the stabilized crystal construction after Ru3+ substitution. Furthermore, the ex-situ XRD/SEM/CV/EIS after cycling indicate the significantly improved kinetic characteristics and enhanced structural stability. Notably, the modified Na3V1.96Ru0.04(PO4)3/C@CNTs reveals superior rate capability and ultralong cyclic performance. It submits high capacities of 82.3/80.9 mAh g-1 at 80/120C and maintains 71.3/59.6 mAh g-1 after 14800/6250 cycles, indicating excellent retention ratios of 86.6 % and 73.6 %, respectively. This work provides a multi-modification strategy for the realization of high-performance cathode materials, which can be widely applied in the optimization of various materials.

Facilitating Layered Oxide Cathodes Based on Orbital Hybridization for Sodium-Ion Batteries: Marvelous Air Stability, Controllable High Voltage, and Anion Redox Chemistry

Layered oxides have become the research focus of cathode materials for sodium-ion batteries (SIBs) due to the low cost, simple synthesis process, and high specific capacity. However, the poor air stability, unstable phase structure under high voltage, and slow anionic redox kinetics hinder their commercial application. In recent years, the concept of manipulating orbital hybridization has been proposed to simultaneously regulate the microelectronic structure and modify the surface chemistry environment intrinsically. In this review, the hybridization modes between atoms in 3d/4d transition metal (TM) orbitals and O 2p orbitals near the region of the Fermi energy level (EF) are summarized based on orbital hybridization theory and first-principles calculations as well as various sophisticated characterizations. Furthermore, the underlying mechanisms are explored from macro-scale to micro-scale, including enhancing air stability, modulating high working voltage, and stabilizing anionic redox chemistry. Meanwhile, the origin, formation conditions, and different types of orbital hybridization, as well as its application in layered oxide cathodes are presented, which provide insights into the design and preparation of cathode materials. Ultimately, the main challenges in the development of orbital hybridization and its potential for the production application are also discussed, pointing out the route for high-performance practical sodium layered oxide cathodes.

Self-terminating, heterogeneous solid-electrolyte interphase enables reversible Li-ether cointercalation in graphite anodes

Ether solvents are suitable for formulating solid-electrolyte interphase (SEI)-less ion-solvent cointercalation electrolytes in graphite for Na-ion and K-ion batteries. However, ether-based electrolytes have been historically perceived to cause exfoliation of graphite and cell failure in Li-ion batteries. In this study, we develop strategies to achieve reversible Li-solvent cointercalation in graphite through combining appropriate Li salts and ether solvents. Specifically, we design 1M LiBF4 1,2-dimethoxyethane (G1), which enables natural graphite to deliver ~91% initial Coulombic efficiency and >88% capacity retention after 400 cycles. We captured the spatial distribution of LiF at various length scales and quantified its heterogeneity. The electrolyte shows self-terminated reactivity on graphite edge planes and results in a grainy, fluorinated pseudo-SEI. The molecular origin of the pseudo-SEI is elucidated by ab initio molecular dynamics (AIMD) simulations. The operando synchrotron analyses further demonstrate the reversible and monotonous phase transformation of cointercalated graphite. Our findings demonstrate the feasibility of Li cointercalation chemistry in graphite for extreme-condition batteries. The work also paves the foundation for understanding and modulating the interphase generated by ether electrolytes in a broad range of electrodes and batteries.

Outstanding long cycle stability provide by bismuth doped Na3V2(PO4)3 enwrapped with carbon nanotubes cathode for sodium-ion batteries

Na3V2(PO4)3 (NVP), possessing good ionic conduction properties and high voltage plateau, has been deemed as the most prospective material for sodium ion batteries. However, the weak intrinsic electronic conductivity has hindered its further commercialization. Herein, an ingenious strategy of Bi3+ substitution at V3+ site in NVP system is proposed. The ionic radius of Bi3+ is slightly larger than that of V3+, which can further expand the crystal structure inside the NVP, thus accelerating the migration of Na+. Meanwhile, the appropriate amount of carbon coating and carbon nanotubes (CNTs) enwrapping construct an effective three-dimensional network, which provides a conductive framework for electronic transfer. Furthermore, the introduction of CNTs also inhibit the agglomeration of active grains during the sintering process, reducing the particle size and shortening the diffusion path of Na+. Comprehensively, the conductivity, ionic diffusion ability and structural stability of the modified Na3V2-xBix(PO4)3/C@CNTs (0 ≤ x ≤ 0.05) sample are significantly improved. The Na3V1.97Bi0.03(PO4)3/C@CNTs sample obtains a reversible capacity of 97.8 mAh g-1 at 12C and maintains a value of 80.6 mAh g-1 after 9000 ultra-long cycles. As for the super high rate at 80C, it exhibits a high capacity of 84.34 mAh g-1 and retains a capacity of 73.34 mAh g-1 after 6000 cycles. The superior electrochemical performance is derived from the enhancement of the crystal structure by Bi3+ doping and the highly conductive network consisting of carbon coating layers and enwrapped CNTs.

3D flower-like hollow MXene@MoS2 heterostructure for fast sodium storage

Constructing an anode with fast electron transport and high cycling stability is important but challenging for large-scale applications of sodium-ion batteries (SIB). In this study, hierarchical flower-like MXene structures were synthesized using poly (methyl methacrylate) (PMMA) microsphere as templates. Subsequently, a straightforward hydrothermal reaction was utilized to anchor small-sized MoS2 nanosheets. The resulting MXene@MoS2 heterostructure exhibits a distinctive three-dimensional (3D) porous hollow architecture. This structure effectively addresses challenges related to self-aggregation of MoS2 nanosheets and volume expansion of the electrode material during Na+ insertion/extraction processes. Furthermore, the robust hetero-interface supports fast and stable electron transfer, thereby enhancing electrochemical reaction kinetics. The prepared MXene@MoS2 electrode demonstrates the specific capacity of 682.1 mA h g-1 at 0.2 A/g and the reversible capacity of 494.4 mA h g-1 after 1000 cycles at 5 A/g. It is noteworthy that the full battery assembled with the composite material as the anode can still maintain the capacity of 456.2 mA h g-1 after 80 cycles at 0.5 A/g. This outstanding reversible capacity and sustained stability over numerous cycles highlights its potential for a wide range of applications.

Scalable Synthesis of Selenide Solid-State Electrolytes for Sodium-Ion Batteries

Solid-state sodium-ion batteries employing superionic solid-state electrolytes (SSEs) offer low manufacturing costs and improved safety and are considered to be a promising alternative to current Li-ion batteries. Solid-state electrolytes must have high chemical/electrochemical stability and superior ionic conductivity. In this work, we employed precursor and solvent engineering to design scalable and cost-efficient solution routes to produce air-stable sodium selenoantimonate (Na3SbSe4). First, a simple metathesis route is demonstrated for the production of the Sb2Se3 precursor that is subsequently used to form ternary Na3SbSe4 through two different routes: alcohol-mediated redox and alkahest amine-thiol approaches. In the former, the electrolyte was successfully synthesized in EtOH by using a similar redox solution coupled with Sb2Se3, Se, and NaOH as a basic reagent. In the alkahest approach, an amine-thiol solvent mixture is utilized for the dissolution of elemental Se and Na and further reaction with the binary precursor to obtain Na3SbSe4. Both routes produced electrolytes with room temperature ionic conductivity (∼0.2 mS cm-1) on par with reported performance from other conventional thermo-mechanical routes. These novel solution-phase approaches showcase the diversity and application of wet chemistry in producing selenide-based electrolytes for all-solid-state sodium batteries.

Lattice-Strain Engineering for Heterogenous Electrocatalytic Oxygen Evolution Reaction

The energy efficiency of metal-air batteries and water-splitting techniques is severely constrained by multiple electronic transfers in the heterogenous oxygen evolution reaction (OER), and the high overpotential induced by the sluggish kinetics has become an uppermost scientific challenge. Numerous attempts are devoted to enabling high activity, selectivity, and stability via tailoring the surface physicochemical properties of nanocatalysts. Lattice-strain engineering as a cutting-edge method for tuning the electronic and geometric configuration of metal sites plays a pivotal role in regulating the interaction of catalytic surfaces with adsorbate molecules. By defining the d-band center as a descriptor of the structure-activity relationship, the individual contribution of strain effects within state-of-the-art electrocatalysts can be systematically elucidated in the OER optimization mechanism. In this review, the fundamentals of the OER and the advancements of strain-catalysts are showcased and the innovative trigger strategies are enumerated, with particular emphasis on the feedback mechanism between the precise regulation of lattice-strain and optimal activity. Subsequently, the modulation of electrocatalysts with various attributes is categorized and the impediments encountered in the practicalization of strained effect are discussed, ending with an outlook on future research directions for this burgeoning field.

Virtual screening of organic quinones as cathode materials for sodium-ion batteries

High-throughput virtual screening (HTVS) has been increasingly applied as an effective approach to find candidate materials for energy applications. We performed a HTVS study, which is powered by: (i) automated virtual screening library generation, (ii) automated search on a readily purchasable chemical space of quinone-based compounds, and (iii) computed physicochemical descriptors for the prediction of key battery-related features of compounds, including the reduction potential, gravimetric energy density, gravimetric charge capacity, and molecular stability. From the initial virtual library of approximately 450k molecules, a total of 326 compounds have been identified as commercially available. Among them, 289 of the molecules are predicted to be stable for the sodiation reactions that take place at the sodium-ion battery cathodes. To study the behaviour of molecules over time at room temperature, we performed molecular dynamics simulations on a group of sodiated product molecules, which was narrowed down to 21 quinones after scrutinizing the key battery performance indicators. As a result, 17 compounds are suggested for validation as candidate cathode materials in sodium-ion batteries.

Ultrathin CuF2 -Rich Solid-Electrolyte Interphase Induced by Cation-Tailored Double Electrical Layer toward Durable Sodium Storage

Solid-electrolyte interphase (SEI) seriously affects battery's cycling life, especially for high-capacity anode due to excessive electrolyte decomposition from particle fracture. Herein, we report an ultrathin SEI (3-4 nm) induced by Cu⁺ -tailored double electrical layer (EDL) to suppress electrolyte consumption and enhance cycling stability of CuS anode in sodium-ion batteries. Unique EDL with SO₃ CF₃ -Cu complex absorbing on CuS in NaSO₃ CF₃ /diglyme electrolyte is demonstrated by in situ surface-enhanced Raman, Cyro-TEM and theoretical calculation, in which SO₃ CF₃ -Cu could be reduced to CuF₂ -rich SEI. Dispersed CuF₂ and F-containing compound can provide good interfacial contact for formation of ultrathin and stable SEI film to minimize electrolyte consumption and reduce activation energy of Na⁺ transport. As a result, the modified CuS delivers high capacity of 402.8 mAh g^-1 after 7000 cycles without capacity decay. The insights of SEI construction pave a way for high-stability electrode.

Amylopectin-Assisted Fabrication of In Situ Carbon-Coated Na3V2(PO4)2F3 Nanosheets for Ultra-Fast Sodium Storage

Na₃V₂(PO₄)₂F₃ is one of the most studied polyanion type cathode materials for sodium-ion batteries (SIBs) and offers great promises. However, the inferior rate capability induced by its sluggish diffusion of electrons and ions greatly limits the practical application of electrode materials in SIBs. Herein, we develop an efficient method to fabricate in situ carbon-coated Na₃V₂(PO₄)₂F₃ nanosheets by using cost-effective amylopectin. The amylopectin not only could induce the nucleation of Na₃V₂(PO₄)₂F₃ along its backbone to form a 2D nanostructure, but also act as a source of amorphous carbon for in situ coating on the active material surface. The composite exhibits extraordinary rate capability (104 mA h g^-1 at 40 C, 51 mA h g^-1 at 150 C) and desirable cycling stability. Such satisfactory achievements, especially the superior rate performance, should be ascribed to its unique 2D nanostructure which shortens the Na⁺ diffusion length, and the in situ carbon coating endows the composites with effective electron transport. Even applied to full cells, the obtained devices still display an exceptionally high energy density (94.8 W h kg^-1), high power density (7295 W kg^-1), and excellent cyclic stability.

Pyridine-based benzoquinone derivatives as organic cathode materials for sodium ion batteries

2,5-Bis(p-benzoquinonyl) pyridine (QPQ-2) was developed as the cathode for sodium-ion batteries.