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.

Linkage Engineering in Covalent Organic Frameworks for Metal-Free Electrocatalytic C2H4 Production from CO2.

Electrocatalytic carbon dioxide reduction reaction (CO2RR) to produce ethylene (C2H4) is conducive to sustainable development of energy and environment. At present, most electrocatalysts for C2H4 production are limited to the heavy metal copper, meanwhile, achieving metal-free catalysis remains a challenge. Noted piperazine with sp3 N hybridization is beneficial to CO2 capture, but CO2RR performance and mechanism have been lacking. Herein, based on linkage engineering, we construct a novel high-density sp3 N catalytic array via introducing piperazine into the crystalline and microporous aminal-linked covalent organic frameworks (COFs). Thanks to its high sp3 N density, strong CO2 capture capacity and great hydrophilicity, aminal-linked COF successfully achieves the conversion of CO2 to C2H4 with a Faraday efficiency up to 19.1 %, which is stand out in all reported metal-free COF electrocatalysts. In addition, a series of imine-linked COFs are synthesized and combined with DFT calculations to demonstrate the critical role of sp3 N in enhancing the kinetics of CO2RR. Therefore, this work reveals the extraordinary potential of linkage engineering in COFs to break through some catalytic bottlenecks.

Reconstructing Helmholtz Plane Enables Robust F-Rich Interface for Long-Life and High-Safe Sodium-Ion Batteries.

Hard carbon (HC) is the most commonly used anode material in sodium-ion batteries. However, the solid-electrolyte-interface (SEI) layer formed in carbonate ester-based electrolytes has an imperceptible dissolution tendency and a sluggish Na+ diffusion kinetics, resulting in unsatisfactory performance of the HC anode. Given that electrode/electrolyte interface property is highly dependent on the configuration of Helmholtz plane, we filtrate proper solvents by PFBE (PF6- anion binding energy) and CAE (carbon absorption energy) and disclose the function of chosen TFEP to reconstruct the Helmholtz plane and regulate the SEI film on HC anode. Benefiting from the preferential adsorption tendency on HC surface and strong anion-dragging interaction of TFEP, a robust and thin anion-derived F-rich SEI film is established, which greatly enhances the mechanical stability and the Na+ ion diffusion kinetics of the electrode/electrolyte interface. The rationally designed TFEP-based electrolyte endows Na||HC half-cell and 2.8 Ah HC||Na4Fe3(PO4)2P2O7 pouch cell with excellent rate capability, long cycle life, high safety and low-temperature adaptability. It is believed that this insightful recognition of tuning interface properties will pave a new avenue on the design of compatible electrolyte for low-cost, long-life, and high-safe sodium-ion batteries.

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.

Thermodynamics and kinetics of Mg2+/Li+ and Mg2+/Na+ co-intercalation into layered titanium disulfide.

Hybrid Mg2+/A+ (A = Li, K, or Na) batteries are promising energy-storage devices combining the merits of a metallic Mg anode and A+ intercalation cathodes. Mg2+/Li+ co-intercalations into the cathodes have been reported, and it is believed that Li-intercalation would reduce the activation energy of the Mg-intercalation and improve the kinetics. Herein, a new understanding of the Mg2+/Li+ and Mg2+/Na+ co-intercalations is revealed for layered TiS2 from the point of view of the thermodynamics and kinetics. In addition to Li-, Na- and Mg-intercalations, Mg-Li (Mg-Na) mixed and Mg-Li (Mg-Na) interlaced intercalations can also be observed. The Mg-Li (Mg-Na) mixed intercalation is co-intercalation of Mg2+ and Li+ (Na+) into the same TiS2 layer, whereas the Mg-Li (Mg-Na) interlaced intercalation means Mg2+ and Li+ (Na+), respectively, intercalate into the adjacent TiS2 layers. The Li- (Na-) intercalation has faster kinetics, whereas the Mg-Li (Mg-Na) interlaced intercalation structure is more stable thermodynamically. The Mg-Li and Mg-Na interlaced intercalations would gradually become the predominant principles of the TiS2-based hybrid Mg2+/Li+ and Mg2+/Na+ batteries, respectively. With this stabilization, both of the hybrid Mg2+/Li+ and Mg2+/Na+ batteries show high capacities, good rate capabilities and stable cycling.

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.

A Solid-Phase Conversion Sulfur Cathode with Full Capacity Utilization and Superior Cycle Stability for Lithium-Sulfur Batteries.

Solid phase conversion sulfur cathode is an effective strategy for eliminating soluble polysulfide intermediates (LiPSs) and improving cyclability of Li-S batteries. However, realizing such a sulfur cathode with high sulfur loading and high capacity utilization is very challenging due to the insulating nature of sulfur. In this work, a strategy is proposed for fabricating solid phase conversion sulfur cathode by encapsulating sulfur in the mesoporous channels of CMK-3 carbon to form a coaxially assembled sulfur/carbon (CA-S/C) composite. Vinyl carbonate (VC) is simultaneously utilized as the electrolyte cosolvent to in-situ form a dense solid electrolyte interface (SEI) on the CA-S/C composite surface through its nucleophilic reaction with the freshly generated polysulfides at the beginning of initial discharge, thus separating the direct contact of interior sulfur with the outer electrolyte. As expected, such a CA-S/C cathode can operate in a solid phase conversion manner in the VC-ether cosolvent electrolyte to exhibit a full capacity utilization (1667 mA h g-1 , ≈100%), a high rate capability of 2.0 A g-1 and excellent long-term cyclability over 500 cycles even at a high sulfur loading (75%, based on the weight of CA-S/C composite), demonstrating great promise for constructing high-energy-density and cycle-stable Li-S batteries.

A Novel Dendrite-Free Lithium Metal Anode via Oxygen and Boron Codoped Honeycomb Carbon Skeleton.

Lithium (Li) metal is an excellent anode of Li ion batteries because of its high theoretical capacity and the low redox potential compared to other anodes. However, the uncontrollable growth of Li dendrites still incurs serious safety issues and poor electrochemical performances, leading to its limited practical application. An oxygen and boron codoped honeycomb carbon skeleton (OBHcCs) is reported and a stable Li metal-based anode is realized. It can be coated on a copper foil substrate to be used as a current collector for a dendrite-free Li metal anode. OBHcCs effectively reduces the local current density owing to the high surface area and inhibits Li dendrite growth, which is explored by scanning electron microscopy and an X-ray photoelectron spectra depth profile. The abundant lithiophilic oxygen and boron-containing functional groups reduce the potential barrier of nucleation and lead to the homogeneous Li ions flux as confirmed by the density functional theories. Therefore, the Li metal anode based on OBHcCs (OBHcCs@Li) stably runs for 700 h in a symmetric cell with a Li stripping capacity of 1 mAh cm-2 at 1 mA cm-2 . Furthermore, the OBHcCs@Li|LiFePO4 full cell shows a good capacity retention of 84.6% with a high coulombic efficiency of 99.6% at 0.5 C for 500 cycles.

Microstructure-Dependent Charge/Discharge Behaviors of Hollow Carbon Spheres and its Implication for Sodium Storage Mechanism on Hard Carbon Anodes.

Hard carbons are actively developed as a promising anode material for sodium ion batteries (SIBs). However, their sodium storage mechanism is poorly understood, leading to difficulties in design and development of high-performance hard carbon anode materials. In this work, hollow carbon spheres (HCSs) with different shell thickness as a model material to investigate the correlation between the microstructural change and resulting Na+ storage behavior during charge/discharge cycles are designed and synthesized. Ex situ X-ray diffraction and Raman evidences reveal that an interlayer spacing change of the graphitic nanodomains occurs in HCS electrode, leading to a shift of the reversible capacity from the high-potential sloping (HPS) region to the low-potential plateau (LPP) region. This unusual capacity shift suggests a microstructure-dependent Na+ storage reaction on the HCS electrode and can be well explained by "adsorption-intercalation" mechanism for these HCS materials. This work strengthens the understanding of the sodium storage behavior and provides a new perspective for the morphological and structural design of hard carbon anode materials for high-performance SIBs.

Understanding and Calibration of Charge Storage Mechanism in Cyclic Voltammetry Curves.

Noticeable pseudo-capacitance behavior out of charge storage mechanism (CSM) has attracted intensive studies because it can provide both high energy density and large output power. Although cyclic voltammetry is recognized as the feasible electrochemical technique to determine it quantitatively in the previous works, the results are inferior due to uncertainty in the definitions and application conditions. Herein, three successive treatments, including de-polarization, de-residual and de-background, as well as a non-linear fitting algorithm are employed for the first time to calibrate the different CSM contribution of three typical cathode materials, LiFePO4 , LiMn2 O4 and Na4 Fe3 (PO4 )2 P2 O7 , and achieve well-separated physical capacitance, pseudo-capacitance and diffusive contributions to the total capacity. This work can eliminate misunderstanding concepts and correct ambiguous results of the pseudo-capacitance contribution and recognize the essence of CSM in electrode materials.

Surface Modification of Fe7 S8 /C Anode via Ultrathin Amorphous TiO2 Layer for Enhanced Sodium Storage Performance.

Iron sulfides with high theoretical capacity and low cost have attracted extensive attention as anode materials for sodium ion batteries. However, the inferior electrical conductivity and devastating volume change and interface instability have largely hindered their practical electrochemical properties. Here, ultrathin amorphous TiO2 layer is constructed on the surface of a metal-organic framework derived porous Fe7 S8 /C electrode via a facile atomic layer deposition strategy. By virtue of the porous structure and enhanced conductivity of the Fe7 S8 /C, the electroactive TiO2 layer is expected to effectively improve the electrode interface stability and structure integrity of the electrode. As a result, the TiO2 -modified Fe7 S8 /C anode exhibits significant performance improvement for sodium-ion batteries. The optimal TiO2 -modified Fe7 S8 /C electrode delivers reversible capacity of 423.3 mA h g-1 after 200 cycles with high capacity retention of 75.3% at 0.2 C. Meanwhile, the TiO2 coating is conducive to construct favorable solid electrolyte interphase, leading to much enhanced initial Coulombic efficiency from 66.9% to 72.3%. The remarkable improvement suggests that the interphase modification holds great promise for high-performance metal sulfide-based anode materials for sodium-ion batteries.

Highly Electrochemically-Reversible Mesoporous Na2 FePO4 F/C as Cathode Material for High-Performance Sodium-Ion Batteries.

As promising cathode materials, iron-based phosphate compounds have attracted wide attention for sodium-ion batteries due to their low cost and safety. Among them, sodium iron fluorophosphate (Na2 FePO4 F) is widely noted due to its layered structure and high operating voltage compared with NaFePO4 . Here, a mesoporous Na2 FePO4 F@C (M-NFPF@C) composite derived from mesoporous FePO4 is synthesized through a facile ball-milling combined calcination method. Benefiting from the mesoporous structure and highly conductive carbon, the M-NFPF@C material exhibits a high reversible capacity of 114 mAh g-1 at 0.1 C, excellent rate capability (42 mAh g-1 at 10 C), and good cycling performance (55% retention after 600 cycles at 5 C). The high plateau capacity obtained (>90% of total capacity) not only shows high electrochemical reversibility of the as-prepared M-NFPF@C but also provides high energy density, which mainly originates from its mesoporous structure derived from the mesoporous FePO4 precursor. The M-NFPF@C serves as a promising cathode material with high performance and low cost for sodium-ion batteries.

Recent Progress in Rechargeable Sodium-Ion Batteries: toward High-Power Applications.

The increasing demands for renewable energy to substitute traditional fossil fuels and related large-scale energy storage systems (EES) drive developments in battery technology and applications today. The lithium-ion battery (LIB), the trendsetter of rechargeable batteries, has dominated the market for portable electronics and electric vehicles and is seeking a participant opportunity in the grid-scale battery market. However, there has been a growing concern regarding the cost and resource availability of lithium. The sodium-ion battery (SIB) is regarded as an ideal battery choice for grid-scale EES owing to its similar electrochemistry to the LIB and the crust abundance of Na resources. Because of the participation in frequency regulation, high pulse-power capability is essential for the implanted SIBs in EES. Herein, a comprehensive overview of the recent advances in the exploration of high-power cathode and anode materials for SIB is presented, and deep understanding of the inherent host structure, sodium storage mechanism, Na+ diffusion kinetics, together with promising strategies to promote the rate performance is provided. This work may shed light on the classification and screening of alternative high rate electrode materials and provide guidance for the design and application of high power SIBs in the future.

Sulfur-Based Electrodes that Function via Multielectron Reactions for Room-Temperature Sodium-Ion Storage.

Emerging rechargeable sodium-ion storage systems-sodium-ion and room-temperature sodium-sulfur (RT-NaS) batteries-are gaining extensive research interest as low-cost options for large-scale energy-storage applications. Owing to their abundance, easy accessibility, and unique physical and chemical properties, sulfur-based materials, in particular metal sulfides (MSx ) and elemental sulfur (S), are currently regarded as promising electrode candidates for Na-storage technologies with high capacity and excellent redox reversibility based on multielectron conversion reactions. Here, we present current understanding of Na-storage mechanisms of the S-based electrode materials. Recent progress and strategies for improving electronic conductivity and tolerating volume variations of the MSx anodes in Na-ion batteries are reviewed. In addition, current advances on S cathodes in RT-NaS batteries are presented. We outline a novel emerging concept of integrating MSx electrocatalysts into conventional carbonaceous matrices as effective polarized S hosts in RT-NaS batteries as well. This comprehensive progress report could provide guidance for research toward the development of S-based materials for the future Na-storage techniques.

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.

Exploring Sodium-Ion Storage Mechanism in Hard Carbons with Different Microstructure Prepared by Ball-Milling Method.

Hard carbon is considered as one of the most promising anodes in sodium-ion batteries due to its high capacity, low cost, and abundant resources. However, the available capacity and low initial Coulombic efficiency (ICE) limits the practical application of hard carbon anode. This issue results from the unclear understanding of the Na+ storage mechanism in hard carbon. In this work, a series of hard carbons with different microstructures are synthesized through an "up to down" approach by using a simple ball-milling method to illustrate the sodium-ion storage mechanism. The results demonstrate that ball-milled hard carbon with more defects and smaller microcrystalline size shows less low-potential-plateau capacity and lower ICE, which provides further evidence to the "adsorption-insertion" mechanism. This work might give a new perspective to design hard carbon material with a proper structure for efficient sodium-ion storage to develop high-performance sodium-ion batteries.

Novel 2D Layered Molybdenum Ditelluride Encapsulated in Few-Layer Graphene as High-Performance Anode for Lithium-Ion Batteries.

Molybdenum ditelluride nanosheets encapsulated in few-layer graphene (MoTe2 /FLG) are synthesized by a simple heating method using Te and Mo powder and subsequent ball milling with graphite. The as-prepared MoTe2 /FLG nanocomposites as anode materials for lithium-ion batteries exhibit excellent electrochemical performance with a highly reversible capacity of 596.5 mAh g-1 at 100 mA g-1 , a high rate capability (334.5 mAh g-1 at 2 A g-1 ), and superior cycling stability (capacity retention of 99.5% over 400 cycles at 0.5 A g-1 ). Ex situ X-ray diffraction and transmission electron microscopy are used to explore the lithium storage mechanism of MoTe2 . Moreover, the electrochemical performance of a MoTe2 /FLG//0.35Li2 MnO3 ·0.65LiMn0.5 Ni0.5 O2 full cell is investigated, which displays a reversible capacity of 499 mAh g-1 (based on the MoTe2 /FLG mass) at 100 mA g-1 and a capacity retention of 78% over 50 cycles, suggesting the promising application of MoTe2 /FLG for lithium-ion storage. First-principles calculations exhibit that the lowest diffusion barrier (0.18 eV) for lithium ions along pathway III in the MoTe2 layered structure is beneficial for improving the Li intercalation/deintercalation property.

High Rate, Long Lifespan LiV3 O8 Nanorods as a Cathode Material for Lithium-Ion Batteries.

LiV3 O8 nanorods with controlled size are successfully synthesized using a nonionic triblock surfactant Pluronic-F127 as the structure directing agent. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques are used to characterize the samples. It is observed that the nanorods with a length of 4-8 µm and diameter of 0.5-1.0 µm distribute uniformly. The resultant LiV3 O8 nanorods show much better performance as cathode materials in lithium-ion batteries than normal LiV3 O8 nanoparticles, which is associated with the their unique micro-nano-like structure that can not only facilitate fast lithium ion transport, but also withstand erosion from electrolytes. The high discharge capacity (292.0 mAh g-1 at 100 mA g-1 ), high rate capability (138.4 mAh g-1 at 6.4 A g-1 ), and long lifespan (capacity retention of 80.5% after 500 cycles) suggest the potential use of LiV3 O8 nanorods as alternative cathode materials for high-power and long-life lithium ion batteries. In particular, the synthetic strategy may open new routes toward the facile fabrication of nanostructured vanadium-based compounds for energy storage applications.

Graphene-Wrapped Na2C12H6O4 Nanoflowers as High Performance Anodes for Sodium-Ion Batteries.

Graphene-wrapped organic nanoflowers are synthesized from ultrasonic treatment of a simple microsized disodium salt (Na212H6O4) and graphene, which demonstrates a greatly enhanced electrochemical capacity, rate capability and cycling stability as organic Na(+) storage anode. This work suggests an effective architecture to make organic materials electrochemically energetic and stable for energy storage applications.