A facile one-step spraying synthesis of MoS₂/C microspheres and their enhanced electrochemical performance as anode of sodium-ion batteries is reported. An aerosol spraying pyrolysis without any template is employed to synthesize MoS₂/C microspheres, in which ultrathin MoS₂ nanosheets (≈2 nm) with enlarged interlayers (≈0.64 nm) are homogeneously embedded in mesoporous carbon microspheres. The as-synthesized mesoporous MoS₂/C microspheres with 31 wt% carbon have been applied as an anode material for sodium ion batteries, demonstrating long cycling stability (390 mAh g⁻¹ after 2500 cycles at 1.0 A g⁻¹) and high rate capability (312 mAh g⁻¹ at 10.0 A g⁻¹ and 244 mAh g⁻¹ at 20.0 A g⁻¹). The superior electrochemical performance is due to the uniform distribution of ultrathin MoS₂ nanosheets in mesoporous carbon frameworks. This kind of structure not only effectively improves the electronic and ionic transport through MoS₂/C microspheres, but also minimizes the influence of pulverization and aggregation of MoS₂ nanosheets during repeated sodiation and desodiation.

We report a rational design of a sulfur heterocyclic quinone (dibenzo[b,i]thianthrene-5,7,12,14-tetraone=DTT) used as a cathode (uptake of four lithium ions to form Li₄DTT) and a conductive polymer [poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)=PEDOT:PSS) used as a binder for a high-performance rechargeable lithium-ion battery. Because of the reduced energy level of the lowest unoccupied molecular orbital (LUMO) caused by the introduced S atoms, the initial Li-ion intercalation potential of DTT is 2.89 V, which is 0.3 V higher than that of its carbon analog. Meanwhile, there is a noncovalent interaction between DTT and PEDOT:PSS, which remarkably suppressed the dissolution and enhanced the conductivity of DTT, thus leading to the great improvement of the electrochemical performance. The DTT cathode with the PEDOT:PSS binder displays a long-term cycling stability (292 mAh g⁻¹ for the first cycle, 266 mAh g⁻¹ after 200 cycles at 0.1 C) and a high rate capability (220 mAh g⁻¹ at 1 C). This design strategy based on a noncovalent interaction is very effective for the application of small organic molecules as the cathode of rechargeable lithium-ion batteries.

Developing rechargeable Na–CO₂ batteries is significant for energy conversion and utilization of CO₂. However, the reported batteries in pure CO₂ atmosphere are non-rechargeable with limited discharge capacity of 200 mAh g⁻¹. Herein, we realized the rechargeability of a Na–CO₂ battery, with the proposed and demonstrated reversible reaction of 3 CO₂+4 Na2 Na₂CO₃+C. The battery consists of a Na anode, an ether-based electrolyte, and a designed cathode with electrolyte-treated multi-wall carbon nanotubes, and shows reversible capacity of 60000 mAh g⁻¹ at 1 A g⁻¹ (≈1000 Wh kg⁻¹) and runs for 200 cycles with controlled capacity of 2000 mAh g⁻¹ at charge voltage <3.7 V. The porous structure, high electro-conductivity, and good wettability of electrolyte to cathode lead to reduced electrochemical polarization of the battery and further result in high performance. Our work provides an alternative approach towards clean recycling and utilization of CO₂.

We report a rational design of a sulfur heterocyclic quinone (dibenzo[b,i]thianthrene-5,7,12,14-tetraone=DTT) used as a cathode (uptake of four lithium ions to form Li₄DTT) and a conductive polymer [poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)=PEDOT:PSS) used as a binder for a high-performance rechargeable lithium-ion battery. Because of the reduced energy level of the lowest unoccupied molecular orbital (LUMO) caused by the introduced S atoms, the initial Li-ion intercalation potential of DTT is 2.89 V, which is 0.3 V higher than that of its carbon analog. Meanwhile, there is a noncovalent interaction between DTT and PEDOT:PSS, which remarkably suppressed the dissolution and enhanced the conductivity of DTT, thus leading to the great improvement of the electrochemical performance. The DTT cathode with the PEDOT:PSS binder displays a long-term cycling stability (292 mAh g⁻¹ for the first cycle, 266 mAh g⁻¹ after 200 cycles at 0.1 C) and a high rate capability (220 mAh g⁻¹ at 1 C). This design strategy based on a noncovalent interaction is very effective for the application of small organic molecules as the cathode of rechargeable lithium-ion batteries.

Developing rechargeable Na–CO₂ batteries is significant for energy conversion and utilization of CO₂. However, the reported batteries in pure CO₂ atmosphere are non-rechargeable with limited discharge capacity of 200 mAh g⁻¹. Herein, we realized the rechargeability of a Na–CO₂ battery, with the proposed and demonstrated reversible reaction of 3 CO₂+4 Na2 Na₂CO₃+C. The battery consists of a Na anode, an ether-based electrolyte, and a designed cathode with electrolyte-treated multi-wall carbon nanotubes, and shows reversible capacity of 60000 mAh g⁻¹ at 1 A g⁻¹ (≈1000 Wh kg⁻¹) and runs for 200 cycles with controlled capacity of 2000 mAh g⁻¹ at charge voltage <3.7 V. The porous structure, high electro-conductivity, and good wettability of electrolyte to cathode lead to reduced electrochemical polarization of the battery and further result in high performance. Our work provides an alternative approach towards clean recycling and utilization of CO₂.

Sodium-ion batteries (SIBs) receive significant attention for electrochemical energy storage and conversion owing to their wide availability and the low cost of Na resources. However, SIBs face challenges of low specific energy, short cycling life, and insufficient specific power, owing to the heavy mass and large radius of Na⁺ ions. As an important component of SIBs, cathode materials have a significant effect on the SIB electrochemical performance. The most recent advances and prospects of inorganic and organic cathode materials are summarized here. Among current cathode materials, layered transition-metal oxides achieve high specific energies around 600 mW h g⁻¹ owing to their high specific capacities of 180–220 mA h g⁻¹ and their moderate operating potentials of 2.7–3.2 V (vs Na⁺/Na). Porous Na₃V₂(PO₄)₃/C nanomaterials exhibit excellent cycling performance with almost 100% retention over 1000 cycles owing to their robust structural framework. Recent emerging cathode materials, such as amorphous NaFePO₄ and pteridine derivatives show interesting electrochemical properties and attractive prospects for application in SIBs. Future work should focus on strategies to enhance the overall performance of cathode materials in terms of specific energy, cycling life, and rate capability with cationic doping, anionic substitution, morphology fabrication, and electrolyte matching.

A simple and template-free method for preparing three-dimensional (3D) porous γ-Fe₂O₃@C nanocomposite is reported using an aerosol spray pyrolysis technology. The nanocomposite contains inner-connected nanochannels and γ-Fe₂O₃ nanoparticles (5 nm) uniformly embedded in a porous carbon matrix. The size of γ-Fe₂O₃ nanograins and carbon content can be controlled by the concentration of the precursor solution. The unique structure of the 3D porous γ-Fe₂O₃@C nanocomposite offers a synergistic effect to alleviate stress, accommodate large volume change, prevent nanoparticles aggregation, and facilitate the transfer of electrons and electrolyte during prolonged cycling. Consequently, the nanocomposite shows high-rate capability and long-term cyclability when applied as an anode material for Na-ion batteries (SIBs). Due to the simple one-pot synthesis technique and high electrochemical performance, 3D porous γ-Fe₂O₃@C nanocomposites have a great potential as anode materials for rechargeable SIBs.

Improving the electrocatalytic oxygen reduction reaction (ORR) activity of transition metal oxides is important for the development of non-noble metal catalysts that are used in metal-air batteries and fuel cells. Here, a novel facile strategy of hydrogenation to significantly enhance the ORR performance of MnO₂. The hydrogenated MnO₂ (H-MnO₂), which is prepared through a simple heat treatment in hydrogen gas, shows characteristics of modified lattice/surface structures and increased electrical conductivity. In 0.1 M KOH aqueous solution, the prepared H-MnO₂ exhibits high activity toward the oxygen electrocatalysis with more positive onset potential (≈60 mV), ≈14% larger of limiting current, lower yield of peroxide species, and better durability than the pristine oxide. Further conductivity testing and density functional theory (DFT) studies reveal the faster kinetics of ORR after hydrogenation is due to the formation of hydrogen bonds and altered microstructure and improved electronic properties. These results highlight the importance of hydrogenation as a facile yet effective strategy to improve the catalytic activity of transition metal oxides for ORR-based applications.

Designed as a high-capacity, high-rate, and long-cycle life anode for sodium-ion batteries, ultrasmall Sn nanoparticles (≈8 nm) homogeneously embedded in spherical carbon network (denoted as 8-Sn@C) is prepared using an aerosol spray pyrolysis method. Instrumental analyses show that 8-Sn@C nanocomposite with 46 wt% Sn and a BET surface area of 150.43 m² g⁻¹ delivers an initial reversible capacity of ≈493.6 mA h g⁻¹ at the current density of 200 mA g⁻¹, a high-rate capacity of 349 mA h g⁻¹ even at 4000 mA g⁻¹, and a stable capacity of ≈415 mA h g⁻¹ after 500 cycles at 1000 mA g⁻¹. The remarkable electrochemical performance of 8-Sn@C is owing to the synergetic effects between the well-dispersed ultrasmall Sn nanoparticles and the conductive carbon network. This unique structure of very-fine Sn nanoparticles embedded in the porous carbon network can effectively suppress the volume fluctuation and particle aggregation of tin during prolonged sodiation/desodiation process, thus solving the major problems of pulverization, loss of electrical contact and low utilization rate facing Sn anode.

Organic carbonyl electrode materials of lithium batteries have shown multifunctional molecule design and high capacity, but have the problems of poor cycling and low rate performance due to their high solubility in traditional carbonate-based electrolytes and low conductivity. High-performance organic lithium batteries with modified ether-based electrolyte (2 m LiN(CF₃SO₂)₂ in 1,3-dioxolane/dimethoxyethane solvent with 1% LiNO₃ additive (2m-DD-1%L)) and 9,10-anthraquinone (AQ)/CMK-3 (AQC) nanocomposite cathode are reported here. The electrochemical results manifest that 2m-DD-1%L electrolyte promotes the cycling performance due to the restraint of AQ dissolution in ether-based electrolyte with high Li salt concentration and formation of a protection film on the surface of the anode. Additionally, the AQC nanocomposite improves the rate performance because of the nanoconfinement effect of CMK-3 and the decrease of charge transfer impedance. In 2m-DD-1%L electrolyte, AQC nanocomposite delivers an initial discharge capacity of 205 mA h g⁻¹ and a capacity of 174 mA h g⁻¹ after 100 cycles at 0.2 C. Even at a high rate of 2 C, its capacity is 146 mA h g⁻¹. This strategy is also used for other organic carbonyl compounds with quinone substructures and they maintain high stable capacities. This sheds light on the development of advanced organic lithium batteries with carbonyl electrode materials and ether-based electrolytes.

Two composites of phosphorus nanoparticles encapsulated in graphene scrolls (P-G) and phosphorus nanoparticles loaded on planar graphene sheets (P/G) were successfully prepared and applied as anodes for sodium-ion batteries. Phosphorus nanoparticles (ca. 100–150 nm) were firstly obtained from commercial red phosphorus by using a simple flotation method. P-G composites with different phosphorus contents (38.6, 52.2, and 62.1 %) were synthesized through a quick-freezing process. In addition, the P/G composite with a phosphorus content of 50.8 % was prepared for comparison purposes. As a result, the P-G composites showed a better performance than the P/G composite. Moreover, the P-G composite with a phosphorus content of 52.2 % showed the best performance, delivering a capacity of 2355 mAh g⁻¹ in the second cycle and 2172 mAh g⁻¹ after 150 cycles at 250 mA g⁻¹ (with a capacity retention of 92.3 %).

MoS₂ nanoflowers with expanded interlayer spacing of the (002) plane were synthesized and used as high-performance anode in Na-ion batteries. By controlling the cut-off voltage to the range of 0.4–3 V, an intercalation mechanism rather than a conversion reaction is taking place. The MoS₂ nanoflower electrode shows high discharge capacities of 350 mAh g⁻¹ at 0.05 A g⁻¹, 300 mAh g⁻¹ at 1 A g⁻¹, and 195 mAh g⁻¹ at 10 A g⁻¹. An initial capacity increase with cycling is caused by peeling off MoS₂ layers, which produces more active sites for Na⁺ storage. The stripping of MoS₂ layers occurring in charge/discharge cycling contributes to the enhanced kinetics and low energy barrier for the intercalation of Na⁺ ions. The electrochemical reaction is mainly controlled by the capacitive process, which facilitates the high-rate capability. Therefore, MoS₂ nanoflowers with expanded interlayers hold promise for rechargeable Na-ion batteries.

MoS₂ nanoflowers with expanded interlayer spacing of the (002) plane were synthesized and used as high-performance anode in Na-ion batteries. By controlling the cut-off voltage to the range of 0.4–3 V, an intercalation mechanism rather than a conversion reaction is taking place. The MoS₂ nanoflower electrode shows high discharge capacities of 350 mAh g⁻¹ at 0.05 A g⁻¹, 300 mAh g⁻¹ at 1 A g⁻¹, and 195 mAh g⁻¹ at 10 A g⁻¹. An initial capacity increase with cycling is caused by peeling off MoS₂ layers, which produces more active sites for Na⁺ storage. The stripping of MoS₂ layers occurring in charge/discharge cycling contributes to the enhanced kinetics and low energy barrier for the intercalation of Na⁺ ions. The electrochemical reaction is mainly controlled by the capacitive process, which facilitates the high-rate capability. Therefore, MoS₂ nanoflowers with expanded interlayers hold promise for rechargeable Na-ion batteries.

Developing organic compounds with multifunctional groups to be used as electrode materials for rechargeable sodium-ion batteries is very important. The organic tetrasodium salt of 2,5-dihydroxyterephthalic acid (Na₄DHTPA; Na₄C₈H₂O₆), which was prepared through a green one-pot method, was investigated at potential windows of 1.6–2.8 V as the positive electrode or 0.1–1.8 V as the negative electrode (vs. Na⁺/Na), each delivering compatible and stable capacities of ca. 180 mAh g⁻¹ with excellent cycling. A combination of electrochemical, spectroscopic and computational studies revealed that reversible uptake/removal of two Na⁺ ions is associated with the enolate groups at 1.6–2.8 V (Na₂C₈H₂O₆/Na₄C₈H₂O₆) and the carboxylate groups at 0.1–1.8 V (Na₄C₈H₂O₆/Na₆C₈H₂O₆). The use of Na₄C₈H₂O₆ as the initial active materials for both electrodes provided the first example of all-organic rocking-chair SIBs with an average operation voltage of 1.8 V and a practical energy density of about 65 Wh kg⁻¹.

Developing organic compounds with multifunctional groups to be used as electrode materials for rechargeable sodium-ion batteries is very important. The organic tetrasodium salt of 2,5-dihydroxyterephthalic acid (Na₄DHTPA; Na₄C₈H₂O₆), which was prepared through a green one-pot method, was investigated at potential windows of 1.6–2.8 V as the positive electrode or 0.1–1.8 V as the negative electrode (vs. Na⁺/Na), each delivering compatible and stable capacities of ca. 180 mAh g⁻¹ with excellent cycling. A combination of electrochemical, spectroscopic and computational studies revealed that reversible uptake/removal of two Na⁺ ions is associated with the enolate groups at 1.6–2.8 V (Na₂C₈H₂O₆/Na₄C₈H₂O₆) and the carboxylate groups at 0.1–1.8 V (Na₄C₈H₂O₆/Na₆C₈H₂O₆). The use of Na₄C₈H₂O₆ as the initial active materials for both electrodes provided the first example of all-organic rocking-chair SIBs with an average operation voltage of 1.8 V and a practical energy density of about 65 Wh kg⁻¹.

Organic redox compounds are emerging electrode materials for rechargeable lithium batteries. However, their electrically insulating nature plagues efficient charge transport within the electroactive bulk. Alternative to the popular solution of elaborating nanocomposite materials, herein we report on a molecular-level engineering strategy towards high-power organic electrode materials with multi-electron reactions. Systematic comparisons of anthraquinone analogues incorporating fused heteroaromatic structures as cathode materials in rechargeable lithium batteries reveal that the judicious incorporation of heteroaromatics improves the cell performance in terms of specific gravimetric capacity, working potential, rate capability, and cyclability. Combination studies with morphological observation, electrochemical impedance characterization, and theoretical modeling provide insight into the advantage of heteroaromatic building blocks. In particular, benzofuro[5,6-b]furan-4,8-dione (BFFD) bearing furan moeities shows a reversible capacity of 181 mAh g⁻¹ when charged/discharged at 100C, corresponding to a power density of 29.8 kW kg⁻¹. These results have pointed to a general design route of high-rate organic electrode materials by rational functionalization of redox compounds with appropriate heteroaromatic units as versatile structural tools.

Organic compounds offer new possibilities for high energy/power density, cost-effective, environmentally friendly, and functional rechargeable lithium batteries. For a long time, they have not constituted an important class of electrode materials, partly because of the large success and rapid development of inorganic intercalation compounds. In recent years, however, exciting progress has been made, bringing organic electrodes to the attention of the energy storage community. Herein thirty years' research efforts in the field of organic compounds for rechargeable lithium batteries are summarized. The working principles, development history, and design strategies of these materials, including organosulfur compounds, organic free radical compounds, organic carbonyl compounds, conducting polymers, non-conjugated redox polymers, and layered organic compounds are presented. The cell performances of these materials are compared, providing a comprehensive overview of the area, and straightforwardly revealing the advantages/disadvantages of each class of materials.

There is an ever-growing demand for rechargeable batteries with reversible and efficient electrochemical energy storage and conversion. Rechargeable batteries cover applications in many fields, which include portable electronic consumer devices, electric vehicles, and large-scale electricity storage in smart or intelligent grids. The performance of rechargeable batteries depends essentially on the thermodynamics and kinetics of the electrochemical reactions involved in the components (i.e., the anode, cathode, electrolyte, and separator) of the cells. During the past decade, extensive efforts have been dedicated to developing advanced batteries with large capacity, high energy and power density, high safety, long cycle life, fast response, and low cost. Here, recent progress in functional materials applied in the currently prevailing rechargeable lithium-ion, nickel-metal hydride, lead acid, vanadium redox flow, and sodium-sulfur batteries is reviewed. The focus is on research activities toward the ionic, atomic, or molecular diffusion and transport; electron transfer; surface/interface structure optimization; the regulation of the electrochemical reactions; and the key materials and devices for rechargeable batteries.

The hydrogen-releasing activity of (LiNH₂)₆–LiH nanoclusters and metal (Na, K, or Mg)-cation substituted nanoclusters (denoted as (NaNH₂)(LiNH₂)₅, (KNH₂)(LiNH₂)₅, and (MgNH)(LiNH₂)₅) are studied using ab initio molecular orbital theory. Kinetics results show that the rate-determining step for the dehydrogenation of the (LiNH₂)₆–LiH nanocluster is the ammonia liberation from the amide with a high activation energy of 167.0 kJ mol⁻¹ (at B3LYP/6-31 + G(d,p) level). However, metal (Na, K, Mg)-cation substitution in amide–hydride nanosystems reduces the activation energies for the rate-determining step to 156.8, 149.6, and 144.1 kJ mol⁻¹ (at B3LYP/6-31 + G(d,p) level) for (NaNH₂)(LiNH₂)₅, (KNH₂)(LiNH₂)₅, and (MgNH)(LiNH₂)₅, respectively. Furthermore, only the −NH₂ group bound to the Na/K cation is destabilized after Na/K cation substitution, indicating that the improving effect from Na/K-cation substitution is due to a short-range interaction. On the other hand, Mg-cation substitution affects all –NH₂ groups in the nanocluster, resulting in weakened N–H covalent bonding together with stronger ionic interactions between Li and the –NH₂ group. The present results shed light on the dehydrogenation mechanisms of metal-cation substitution in lithium amide–hydride nanoclusters and the application of (MgNH)(LiNH₂)₅ nanoclusters as promising hydrogen-storage media.