Designing Advanced Electrolytes for High-Safety and Long-Lifetime Sodium-Ion Batteries via Anion-Cation Interaction Modulation.

Safety hazards caused by flammable electrolytes have been major obstacles to the practical application of sodium-ion batteries (SIBs). The adoption of nonflammable all-phosphate electrolytes can effectively improve the safety of SIBs; however, traditional low-concentration phosphate electrolytes are not compatible with carbon-based anodes. Herein, we report an anion-cation interaction modulation strategy to design low-concentration phosphate electrolytes with superior physicochemical properties. Tris(2,2,2-trifluoroethyl) phosphate (TFEP) is introduced as a cosolvent to regulate the ion-solvent-coordinated (ISC) structure through enhancing the anion-cation interactions, forming the stable anion-induced ISC (AI-ISC) structure, even at a low salt concentration (1.22 M). Through spectroscopy analyses and theoretical calculations, we reveal the underlying mechanism responsible for the stabilization of these electrolytes. Impressively, both the hard carbon (HC) anode and Na4Fe2.91(PO4)2(P2O7) (NFPP) cathode work well with the developed electrolytes. The designed phosphate electrolyte enables Ah-level HC//NFPP pouch cells with an average Coulombic efficiency (CE) of over 99.9% and a capacity retention of 84.5% after 2000 cycles. In addition, the pouch cells can operate in a wide temperature range (-20 to 60 °C) and successfully pass rigorous safety testing. This work provides new insight into the design of the electrochemically compatibility electrolyte for high-safety and long-lifetime SIBs.

LiNO3 -Based Electrolytes via Electron-Donation Modulation for Sustainable Nonaqueous Lithium Rechargeable Batteries.

LiPF6 as a dominant lithium salt of electrolyte is widely used in commercial rechargeable lithium-ion batteries due to its well-balanced properties, including high solubility in organic solvents, good electrochemical stability, and high ionic conductivity. However, it suffers from several undesirable properties, such as high moisture sensitivity, thermal instability, and high cost. To address these issues, herein, we propose an electron-donation modulation (EDM) rule for the development of low-cost, sustainable, and electrochemically compatible LiNO3 -based electrolytes. We employ high donor-number solvents (HDNSs) with strong electron-donation ability to dissolve LiNO3 , while low donor-number solvents (LDNSs) with weak electron-donation ability are used to regulate the solvation structure to stabilize the electrolytes. As an example, we design the LiNO3 -DMSO@PC electrolyte, where DMSO acts as an HDNS and PC serves as an LDNS. This electrolyte exhibits excellent electrochemical compatibility with graphite anodes, as well as the LiFePO4 and LiCoO2 cathodes, leading to stable cycling over 200 cycles. Through spectroscopy analyses and theoretical calculation, we uncover the underlying mechanism responsible for the stabilization of these electrolytes. Our findings provide valuable insights into the preparation of LiNO3 -based electrolytes using the EDM rule, opening new avenues for the development of advanced electrolytes with versatile functions for sustainable rechargeable batteries.

Aromatic Ketones as Mild Presodiating Reagents toward Cathodes for High-Performance Sodium-Ion Batteries.

Chemical presodiation (CP) is an effective strategy to enhance energy density of sodium ion batteries. However, the sodiation reagents reported so far are basically polycyclic aromatic hydrocarbons (PAHs) wth low reductive potential (~0.1 V vs. Na+ /Na), which could easily cause over-sodiation and structural deterioration of the presodiated cathodes. In this work, Aromatic ketones (AKs) are rationally designed as mild presodiating reagents by introducing a carbonyl group (C=O) into PAHs to balance the conjugated and inductive effect. As the representatives, two compounds 9-Fluorenoneb (9-FN) and Benzophenone (BP) manifest favorable equilibrium potential of 1.55 V and 1.07 V (vs. Na+ /Na), respectively. Note that 9-FN demonstrates versatile presodiating capability toward multiple Na uptake hosts (tunneled Na0.44 MnO2 , layered Na0.67 Ni0.33 Mn0.67 O2 , polyanionic Na4 Fe2.91 (PO4 )2 P2 O7 , Na3 V2 (PO4 )3 and Na3 V2 (PO4 )2 F3 ), enabling greatly improved initial charging capacity of the cathode to balance the irrevisible capacity of the anode. Our results indicate that the Aromatic ketones are competitive presodiating cathodic reagents for high-performance sodium-ion batteries, and will inspire more studies and application attempts in the future.

Doping Regulation in Polyanionic Compounds for Advanced Sodium-Ion Batteries.

It has long been the goal to develop rechargeable batteries with low cost and long cycling life. Polyanionic compounds offer attractive advantages of robust frameworks, long-term stability, and cost-effectiveness, making them ideal candidates as electrode materials for grid-scale energy storage systems. In the past few years, various polyanionic electrodes have been synthesized and developed for sodium storage. Specifically, doping regulation including cation and anion doping has shown a great effect in tailoring the structures of polyanionic electrodes to achieve extraordinary electrochemical performance. In this review, recent progress in doping regulation in polyanionic compounds as electrode materials for sodium-ion batteries (SIBs) is summarized, and their underlying mechanisms in improving electrochemical properties are discussed. Moreover, challenges and prospects for the design of advanced polyanionic compounds for SIBs are put forward. It is anticipated that further versatile strategies in developing high-performance electrode materials for advanced energy storage devices can be inspired.

Correlating the Solvating Power of Solvents with the Strength of Ion-Dipole Interaction in Electrolytes of Lithium-ion Batteries.

The solvation structure of Li+ plays a significant role in determining the physicochemical properties of electrolytes. However, to date, there is still no clear definition of the solvating power of different electrolyte solvents, and even the solvents that preferentially participate in the solvation structure remain controversial. In this study, we comprehensively discuss the solvating power and solvation process of Li+ ions using both experimental characterizations and theoretical calculations. Our findings reveal that the solvating power is dependent on the strength of the Li+ -solvent (ion-dipole) interaction. Additionally, we uncover that the anions tend to enter the solvation sheath in most electrolyte systems through Li+ -anion (ion-ion) interaction, which is weakened by the shielding effect of solvents. The competition between the Li+ -solvent and Li+ -anion interactions ultimately determines the final solvation structures. This insight into the fundamental understanding of the solvation structure of Li+ provides inspiration for the design of multifunctional mixed-solvent electrolytes for advanced batteries.

Metal-Organic Frameworks Derived Functional Materials for Electrochemical Energy Storage and Conversion: A Mini Review.

With many apparent advantages including high surface area, tunable pore sizes and topologies, and diverse periodic organic-inorganic ingredients, metal-organic frameworks (MOFs) have been identified as versatile precursors or sacrificial templates for preparing functional materials as advanced electrodes or high-efficiency catalysts for electrochemical energy storage and conversion (EESC). In this Mini Review, we first briefly summarize the material design strategies to show the rich possibilities of the chemical compositions and physical structures of MOFs derivatives. We next highlight the latest advances focusing on the composition/structure/performance relationship and discuss their practical applications in various EESC systems, such as supercapacitors, rechargeable batteries, fuel cells, water electrolyzers, and carbon dioxide/nitrogen reduction reactions. Finally, we provide some of our own insights into the major challenges and prospective solutions of MOF-derived functional materials for EESC, hoping to shed some light on the future development of this highly exciting field.

Rational Design and Engineering of One-Dimensional Hollow Nanostructures for Efficient Electrochemical Energy Storage.

The unique structural characteristics of one-dimensional (1D) hollow nanostructures result in intriguing physicochemical properties and wide applications, especially for electrochemical energy storage applications. In this Minireview, we give an overview of recent developments in the rational design and engineering of various kinds of 1D hollow nanostructures with well-designed architectures, structural/compositional complexity, controllable morphologies, and enhanced electrochemical properties for different kinds of electrochemical energy storage applications (i.e. lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, lithium-selenium sulfur batteries, lithium metal anodes, metal-air batteries, supercapacitors). We conclude with prospects on some critical challenges and possible future research directions in this field. It is anticipated that further innovative studies on the structural and compositional design of functional 1D nanostructured electrodes for energy storage applications will be stimulated.

Nitrogen-Doped Amorphous Zn-Carbon Multichannel Fibers for Stable Lithium Metal Anodes.

The application of lithium metal anodes for practical batteries is still impeded by safety issues and low Coulombic efficiency caused mainly by the uncontrollable growth of lithium dendrites. Herein, two types of free-standing nitrogen-doped amorphous Zn-carbon multichannel fibers are synthesized as multifunctional hosts for lithium accommodation. The 3D macroporous structures endow effectively reduced local current density, and the lithiophilic nitrogen-doped carbon and functional Zn nanoparticles serve as preferred deposition sites with low nucleation barriers to guide uniform lithium deposition. As a result, the developed anodes exhibit remarkable electrochemical properties in terms of high Coulombic efficiency for more than 500 cycles at various current densities from 1 to 5 mA cm-2 , and symmetric cells show long-term cycling duration over 2000 h. Moreover, full cells based on the developed anode and a LiFePO4 cathode also demonstrate superior rate capability and stable cycle life.

Rationally Designed Three-Layered Cu2 S@Carbon@MoS2 Hierarchical Nanoboxes for Efficient Sodium Storage.

Hybrid materials, integrating the merits of individual components, are ideal structures for efficient sodium storage. However, the construction of hybrid structures with decent physical/electrochemical properties is still challenging. Now, the elaborate design and synthesis of hierarchical nanoboxes composed of three-layered Cu2 S@carbon@MoS2 as anode materials for sodium-ion batteries is reported. Through a facile multistep template-engaged strategy, ultrathin MoS2 nanosheets are grown on nitrogen-doped carbon-coated Cu2 S nanoboxes to realize the Cu2 S@carbon@MoS2 configuration. The design shortens the diffusion path of electrons/Na+ ions, accommodates the volume change of electrodes during cycling, enhances the electric conductivity of the hybrids, and offers abundant active sites for sodium uptake. By virtue of these advantages, these three-layered Cu2 S@carbon@MoS2 hierarchical nanoboxes show excellent electrochemical properties in terms of decent rate capability and stable cycle life.

Synthesis of Copper-Substituted CoS2 @Cux S Double-Shelled Nanoboxes by Sequential Ion Exchange for Efficient Sodium Storage.

The construction of hybrid architectures for electrode materials has been demonstrated as an efficient strategy to boost sodium-storage properties because of the synergetic effect of each component. However, the fabrication of hybrid nanostructures with a rational structure and desired composition for effective sodium storage is still challenging. In this study, an integrated nanostructure composed of copper-substituted CoS2 @Cux S double-shelled nanoboxes (denoted as Cu-CoS2 @Cux S DSNBs) was synthesized through a rational metal-organic framework (MOF)-based templating strategy. The unique shell configuration and complex composition endow the Cu-CoS2 @Cux S DSNBs with enhanced electrochemical performance in terms of superior rate capability and stable cyclability.

Co3 O4 Hollow Nanoparticles Embedded in Mesoporous Walls of Carbon Nanoboxes for Efficient Lithium Storage.

Confining nanostructured electrode materials in porous carbon represents an effective strategy for improving the electrochemical performance of lithium-ion batteries. Herein, we report the design and synthesis of hybrid hollow nanostructures composed of highly dispersed Co3 O4 hollow nanoparticles (sub-20 nm) embedded in the mesoporous walls of carbon nanoboxes (denoted as H-Co3 O4 @MCNBs) as an anode material for lithium-ion batteries. The facile metal-organic framework (MOF)-engaged strategy for the synthesis of H-Co3 O4 @MCNBs involves chemical etching-coordination and subsequent two-step annealing treatments. Owing to the unique structural merits including more active interfacial sites, effectively alleviated volume variation, good and stable electrical contact, and easy access of Li+ ions, the H-Co3 O4 @MCNBs exhibit excellent lithium-storage performance in terms of high specific capacity, excellent rate capability, and cycling stability.

Double-Shelled C@MoS2 Structures Preloaded with Sulfur: An Additive Reservoir for Stable Lithium Metal Anodes.

The growth of Li dendrites hinders the practical application of lithium metal anodes (LMAs). In this work, a hollow nanostructure, based on hierarchical MoS2 coated hollow carbon particles preloaded with sulfur (C@MoS2 /S), was designed to modify the LMA. The C@MoS2 hollow nanostructures serve as a good scaffold for repeated Li plating/stripping. More importantly, the encapsulated sulfur could gradually release lithium polysulfides during the Li plating/stripping, acting as an effective additive to promote the formation of a mosaic solid electrolyte interphase layer embedded with crystalline hybrid lithium-based components. These two factors together effectively suppress the growth of Li dendrites. The as-modified LMA shows a high Coulombic efficiency of 98 % over 500 cycles at the current density of 1 mA cm-2 . When matched with a LiFePO4 cathode, the assembled full cell displays a highly improved cycle life of 300 cycles, implying the feasibility of the proposed LMA.

Hierarchical Microboxes Constructed by SnS Nanoplates Coated with Nitrogen-Doped Carbon for Efficient Sodium Storage.

The design and synthesis of hierarchical microboxes, assembled from SnS nanoplates coated with nitrogen-doped carbon (NC) as an anode material for sodium-ion batteries, is demonstrated. The template-engaged multistep synthesis of the SnS@NC microboxes involves sequential phase transformation, polydopamine coating, and thermal annealing in N2 . The SnS@NC composite with two-dimensional nano-sized subunits rationally integrates several advantages including shortening the diffusion path of electrons/Na+ ions, improving electric conductivity, and alleviating volume variation of the electrode material. As a result, the SnS@NC microboxes show efficient sodium storage performance with high capacity, good cycling stability, and excellent rate capability.

Synthesis of CuS@CoS2 Double-Shelled Nanoboxes with Enhanced Sodium Storage Properties.

Metal sulfides have received considerable attention for efficient sodium storage owing to their high capacity and decent redox reversibility. However, the poor rate capability and fast capacity decay greatly hinder their practical application in sodium-ion batteries. Herein, an elegant multi-step templating strategy has been developed to rationally synthesize hierarchical double-shelled nanoboxes with the CoS2 nanosheet-constructed outer shell supported on the CuS inner shell. Their structure and composition enable these hierarchical CuS@CoS2 nanoboxes to show boosted electrochemical properties with high capacity, outstanding rate capability, and long cycle life.

Bullet-like Cu9 S5 Hollow Particles Coated with Nitrogen-Doped Carbon for Sodium-Ion Batteries.

Metal sulfides with excellent redox reversibility and high capacity are very promising electrode materials for sodium-ion batteries. However, their practical application is still hindered by the poor rate capability and limited cycle life. Herein, a template-based strategy is developed to synthesize nitrogen-doped carbon-coated Cu9 S5 bullet-like hollow particles starting from bullet-like ZnO particles. With the structural and compositional advantages, these unique nitrogen-doped carbon-coated Cu9 S5 bullet-like hollow particles manifest excellent sodium storage properties with superior rate capability and ultra-stable cycling performance.

Synthesis of Cobalt Sulfide Multi-shelled Nanoboxes with Precisely Controlled Two to Five Shells for Sodium-Ion Batteries.

We report the synthesis of cobalt sulfide multi-shelled nanoboxes through metal-organic framework (MOF)-based complex anion conversion and exchange processes. The polyvanadate ions react with cobalt-based zeolitic imidazolate framework-67 (ZIF-67) nanocubes to form ZIF-67/cobalt polyvanadate yolk-shelled particles. The as-formed yolk-shelled particles are gradually converted into cobalt divanadate multi-shelled nanoboxes by solvothermal treatment. The number of shells can be easily controlled from 2 to 5 by varying the temperature. Finally, cobalt sulfide multi-shelled nanoboxes are produced through ion-exchange with S2- ions and subsequent annealing. The as-obtained cobalt sulfide multi-shelled nanoboxes exhibit enhanced sodium-storage properties when evaluated as anodes for sodium-ion batteries. For example, a high specific capacity of 438 mAh g-1 can be retained after 100 cycles at the current density of 500 mA g-1 .

Recent Progress in Iron-Based Electrode Materials for Grid-Scale Sodium-Ion Batteries.

Grid-scale energy storage batteries with electrode materials made from low-cost, earth-abundant elements are needed to meet the requirements of sustainable energy systems. Sodium-ion batteries (SIBs) with iron-based electrodes offer an attractive combination of low cost, plentiful structural diversity and high stability, making them ideal candidates for grid-scale energy storage systems. Although various iron-based cathode and anode materials have been synthesized and evaluated for sodium storage, further improvements are still required in terms of energy/power density and long cyclic stability for commercialization. In this Review, progress in iron-based electrode materials for SIBs, including oxides, polyanions, ferrocyanides, and sulfides, is briefly summarized. In addition, the reaction mechanisms, electrochemical performance enhancements, structure-composition-performance relationships, merits and drawbacks of iron-based electrode materials for SIBs are discussed. Such iron-based electrode materials will be competitive and attractive electrodes for next-generation energy storage devices.

Formation of Polypyrrole-Coated Sb2 Se3 Microclips with Enhanced Sodium-Storage Properties.

Antimony-based electrode materials with high specific capacity have aroused considerable interest as anode materials for sodium-ion batteries (SIBs). Herein, we develop a template-engaged ion-exchange method to synthesize Sb2 Se3 microclips, and the as-obtained Sb2 Se3 microclips are further in situ coated with polypyrrole (PPy). Benefiting from the structural and compositional merits, these PPy-coated Sb2 Se3 microclips exhibit enhanced sodium-storage properties in terms of high reversible capacity, superior rate capability, and stable cycling performance.

A Practical High-Energy Cathode for Sodium-Ion Batteries Based on Uniform P2-Na0.7 CoO2 Microspheres.

Layered metal oxides have attracted increasing attention as cathode materials for sodium-ion batteries (SIBs). However, the application of such cathode materials is still hindered by their poor rate capability and cycling stability. Here, a facile self-templated strategy is developed to synthesize uniform P2-Na0.7 CoO2 microspheres. Due to the unique microsphere structure, the contact area of the active material with electrolyte is minimized. As expected, the P2-Na0.7 CoO2 microspheres exhibit enhanced electrochemical performance for sodium storage in terms of high reversible capacity (125 mAh g-1 at 5 mA g-1 ), superior rate capability and long cycle life (86 % capacity retention over 300 cycles). Importantly, the synthesis method can be easily extended to synthesize other layered metal oxide (P2-Na0.7 MnO2 and O3-NaFeO2 ) microspheres.

Hierarchical Nanotubes Constructed by Carbon-Coated Ultrathin SnS Nanosheets for Fast Capacitive Sodium Storage.

Tin(II) sulfide (SnS) has been an attractive anode material for sodium ion batteries. Herein, an elegant templating method has been developed for the rational design and synthesis of hierarchical SnS nanotubes composed of ultrathin nanosheets. In order to enhance the electrochemical performance, carbon coated hierarchical SnS nanotubes (denoted as SnS@C nanotubes) have also been obtained by simply adding glucose into the reaction system. Benefiting from their unique structural merits, the SnS@C nanotubes exhibit enhanced sodium storage properties in terms of good cycling performance and superior rate capability.