Multiregion Janus-Featured Cobalt Phosphide-Cobalt Composite for Highly Reversible Room-Temperature Sodium-Sulfur Batteries

Electrode materials with high conductivity, strong chemisorption, and catalysis toward polysulfides are recognized as key factors for metal-sulfur batteries. Nevertheless, the construction of such functional material is a challenge for room-temperature sodium-sulfur (RT-Na/S) batteries. Herein, a multiregion Janus-featured CoP-Co structure obtained via sequential carbonization-oxidation-phosphidation of heteroseed zeolitic imidazolate frameworks is introduced. The structural virtues include a heterostructure existing in a CoP-Co structure and a conductive network of N-doped porous carbon nanotube hollow cages (NCNHCs), endowing it with superior conductivity in both the short- and long-range and strong polarity toward polysulfides. Thus, the S@CoP-Co/NCNHC cathode exhibits superior electrochemical performance (448 mAh g^-1 remained for 700 times cycling under 1 A g^-1) and an optimized redox mechanism in polysulfides conversion. Density functional theory calculations present that the CoP-Co structure optimizes bond structure and bandwidth, whereas the pure CoP is lower than the corresponding Fermi level, which could essentially benefit the adsorptive capability and charge transfer from the CoP-Co surface to Na₂S_x and therefore improve its affinity to polysulfides.

Self-assembling RuO2 nanogranulates with few carbon layers as an interconnected nanoporous structure for lithium-oxygen batteries

Electrocatalysis for cathodic oxygen is of great significance for achieving high-performance lithium-oxygen batteries. Herein, we report a facile and green method to prepare an interconnected nanoporous three-dimensional (3D) architecture, which is composed of RuO2 nanogranulates coated with few layers of carbon. The as-prepared 3D nanoporous RuO2@C nanostructure can demonstrate a high initial specific discharge capacity of 4000 mA h g-1 with high round-trip efficiency of 95%. Meanwhile, the nanoporous RuO2@C could achieve stable cycling performance with a fixed capacity of 1500 mA h g-1 over 100 cycles. The terminal discharge and charge potentials of nanoporous RuO2@C are well maintained with minor potential variation of 0.14 and 0.13 V at the 100th cycle, respectively. In addition, the formation of discharge products is monitored by using in situ high-energy synchrotron X-ray diffraction (XRD).

Ultrathin 2D Mesoporous TiO2 /rGO Heterostructure for High-Performance Lithium Storage

Lithium-ion batteries (LIBs) have been widely applied and studied as an effective energy supplement for a variety of electronic devices. Titanium dioxide (TiO₂ ), with a high theoretical capacity (335 mAh g^-1 ) and low volume expansion ratio upon lithiation, has been considered as one of the most promising anode materials for LIBs. However, the application of TiO₂ is hindered by its low electrical conductivity and slow ionic diffusion rate. Herein, a 2D ultrathin mesoporous TiO₂ /reduced graphene (rGO) heterostructure is fabricated via a layer-by-layer assembly process. The synergistic effect of ultrathin mesoporous TiO₂ and the rGO nanosheets significantly enhances the ionic diffusion and electron conductivity of the composite. The introduced 2D mesoporous heterostructure delivers a significantly improved capacity of 350 mAh g^-1 at a current density of 200 mA g^-1 and excellent cycling stability, with a capacity of 245 mAh g^-1 maintained over 1000 cycles at a high current density of 1 A g^-1 . The in situ transmission electron microscopy analysis indicates that the volume of the as-prepared 2D heterostructures changes slightly upon the insertion and extraction of Li⁺ , thus contributing to the enhanced long-cycle performance.

Full Activation of Mn4+ /Mn3+ Redox in Na4 MnCr(PO4 )3 as a High-Voltage and High-Rate Cathode Material for Sodium-Ion Batteries

Developing high-voltage cathode materials is critical for sodium-ion batteries to boost energy density. NASICON (Na super-ionic conductor)-structured Na_x MnM(PO₄ )₃ materials (M represents transition metal) have drawn increasing attention due to their features of robust crystal framework, low cost, as well as high voltage based on Mn⁴⁺ /Mn³⁺ and Mn³⁺ /Mn²⁺ redox couples. However, full activation of Mn⁴⁺ /Mn³⁺ redox couple within NASICON framework is still a great challenge. Herein, a novel NASICON-type Na₄ MnCr(PO₄ )₃ material with highly reversible Mn⁴⁺ /Mn³⁺ redox reaction is discovered. It proceeds a two-step reaction with voltage platforms centered at 4.15 and 3.52 V versus Na⁺ /Na, delivering a capacity of 108.4 mA h g^-1 . The Na₄ MnCr(PO₄ )₃ cathode also exhibits long durability over 500 cycles and impressive rate capability up to 10 C. The galvanostatic intermittent titration technique (GITT) test shows fast Na diffusivity which is further verified by density functional theory calculations. The high electrochemical activity derives from the 3D robust framework structure, fast kinetics, and pseudocapacitive contribution. The sodium storage mechanism of the Na₄ MnCr(PO₄ )₃ cathode is deeply studied by ex situ X-ray diffraction (XRD) and ex situ X-ray photoelectron spectroscopy (XPS), revealing that both solid-solution and two-phase reactions are involved in the Na⁺ ions extraction/insertion process.

Remedies for Polysulfide Dissolution in Room-Temperature Sodium-Sulfur Batteries

Rechargeable room-temperature sodium-sulfur (RT-NaS) batteries represent one of the most attractive technologies for future stationary energy storage due to their high energy density and low cost. The S cathodes can react with Na ions via two-electron conversion reactions, thus achieving ultrahigh theoretical capacity (1672 mAh g^-1 ) and specific energy (1273 Wh kg^-1 ). Unfortunately, the sluggish reaction kinetics of the nonconductive S, severe polysulfide dissolution, and the use of metallic Na are causing enormous challenges for the development of RT-NaS batteries. Fatal polysulfide dissolution is highlighted, important studies toward polysulfide immobilization and conversion are presented, and the reported remedies in terms of intact physical confinement, strong chemical interaction, blocking layers, and optimization of electrolytes are summarized. Future research directions toward practical RT-NaS batteries are summarized.

A High-Kinetics Sulfur Cathode with a Highly Efficient Mechanism for Superior Room-Temperature Na-S Batteries

Applications of room-temperature-sodium sulfur (RT-Na/S) batteries are currently impeded by the insulating nature of sulfur, the slow redox kinetics of sulfur with sodium, and the dissolution and migration of sodium polysulfides. Herein, a novel micrometer-sized hierarchical S cathode supported by FeS₂ electrocatalyst, which is grown in situ in well-confined carbon nanocage assemblies, is presented. The hierarchical carbon matrix can provide multiple physical entrapment to polysulfides, and the FeS₂ nanograins exhibit a low Na-ion diffusion barrier, strong binding energy, and high affinity for sodium polysulfides. Their combination makes it an ideal sulfur host to immobilize the polysulfides and achieve reversible conversion of polysulfides toward Na₂ S. Importantly, the hierarchical S cathode is suitable for large-scale production via the inexpensive and green spray-drying method. The porous hierarchical S cathode offers a high sulfur content of 65.5 wt%, and can deliver high reversible capacity (524 mAh g^-1 over 300 cycles at 0.1 A g^-1 ) and outstanding rate capability (395 mAh g^-1 at 1 A g^-1 for 850 cycles), holding great promise for both scientific research and real application.

Nickel sulfide nanocrystals on nitrogen-doped porous carbon nanotubes with high-efficiency electrocatalysis for room-temperature sodium-sulfur batteries

Polysulfide dissolution and slow electrochemical kinetics of conversion reactions lead to low utilization of sulfur cathodes that inhibits further development of room-temperature sodium-sulfur batteries. Here we report a multifunctional sulfur host, NiS₂ nanocrystals implanted in nitrogen-doped porous carbon nanotubes, which is rationally designed to achieve high polysulfide immobilization and conversion. Attributable to the synergetic effect of physical confinement and chemical bonding, the high electronic conductivity of the matrix, closed porous structure, and polarized additives of the multifunctional sulfur host effectively immobilize polysulfides. Significantly, the electrocatalytic behaviors of the Lewis base matrix and the NiS₂ component are clearly evidenced by operando synchrotron X-ray diffraction and density functional theory with strong adsorption of polysulfides and high conversion of soluble polysulfides into insoluble Na₂S₂/Na₂S. Thus, the as-obtained sulfur cathodes exhibit excellent performance in room-temperature Na/S batteries.

Room temperature rechargeable sodium sulfur batteries are promising for next-generation energy storage systems, but their development is limited by polysulfide dissolution and slow kinetics. Here the authors report a cathode that serves as a multifunctional sulfur host and imparts enhanced performance.

Chemical Properties, Structural Properties, and Energy Storage Applications of Prussian Blue Analogues

Prussian blue analogues (PBAs, A₂ T[M(CN)₆ ], A = Li, K, Na; T = Fe, Co, Ni, Mn, Cu, etc.; M = Fe, Mn, Co, etc.) are a large family of materials with an open framework structure. In recent years, they have been intensively investigated as active materials in the field of energy conversion and storage, such as for alkaline-ion batteries (lithium-ion, LIBs; sodium-ion, NIB; and potassium-ion, KIBs), and as electrochemical catalysts. Nevertheless, few review papers have focused on the intrinsic chemical and structural properties of Prussian blue (PB) and its analogues. In this Review, a comprehensive insight into the PBAs in terms of their structural and chemical properties, and the effects of these properties on their materials synthesis and corresponding performance is provided.

Recent Progress of Layered Transition Metal Oxide Cathodes for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are attracting increasing attention and considered to be a low-cost complement or an alternative to lithium-ion batteries (LIBs), especially for large-scale energy storage. Their application, however, is limited because of the lack of suitable host materials to reversibly intercalate Na⁺ ions. Layered transition metal oxides (Na_x MO₂ , M = Fe, Mn, Ni, Co, Cr, Ti, V, and their combinations) appear to be promising cathode candidates for SIBs due to their simple structure, ease of synthesis, high operating potential, and feasibility for commercial production. In the present work, the structural evolution, electrochemical performance, and recent progress of Na_x MO₂ as cathode materials for SIBs are reviewed and summarized. Moreover, the existing drawbacks are discussed and several strategies are proposed to help alleviate these issues. In addition, the exploration of full cells based on Na_x MO₂ cathodes and future perspectives are discussed to provide guidance for the future commercialization of such systems.

Morphology tuning of inorganic nanomaterials grown by precipitation through control of electrolytic dissociation and supersaturation

The precise control of the morphology of inorganic materials during their synthesis is important yet challenging. Here we report that the morphology of a wide range of inorganic materials, grown by rapid precipitation from a metal cation solution, can be tuned during their crystallization from one- to three-dimensional (1D to 3D) structures without the need for capping agents or templates. This control is achieved by adjusting the balance between the electrolytic dissociation (α) of the reactants and the supersaturation (S) of the solutions. Low-α, weak electrolytes promoted the growth of anisotropic (1D and 2D) samples, with 1D materials favoured in particular at low S. In contrast, isotropic 3D polyhedral structures could only be prepared in the presence of strong electrolyte reactants (α ≈ 1) with low S. Using this strategy, a wide range of materials were prepared, including metal oxides, hydroxides, carbonates, molybdates, oxalates, phosphates, fluorides and iodate with a variety of morphologies.

Ultraflexible Transparent Bio-Based Polymer Conductive Films Based on Ag Nanowires

The unstable mechanical properties of flexible transparent conductive films (TCFs) make it difficult for them to meet the requirements for displays or wearable devices. Here, the relationship between the mechanism behind the bending behavior and the electrical properties, which is important for improving the mechanical stability of flexible TCFs, is explored. Flexible TCFs are reported based on silver nanowires (AgNWs) and bio-based poly(ethylene-co-1,4-cyclohexanedimethylene 2,5-furandicarboxylate)s (PECFs), with a low sheet resistance (23.8 Ω sq^-1 at 84.6% transmittance) and superior mechanical properties. The electrical properties of the AgNW/PECFs composite film show almost no change after bending for 2000 times.

A Hydrostable Cathode Material Based on the Layered P2@P3 Composite that Shows Redox Behavior for Copper in High-Rate and Long-Cycling Sodium-Ion Batteries

Low-cost layered oxides free of Ni and Co are considered to be the most promising cathode materials for future sodium-ion batteries. Biphasic Na_0.78 Cu_0.27 Zn_0.06 Mn_0.67 O₂ obtained via superficial atomic-scale P3 intergrowth with P2 phase induced by Zn doping, consisting of inexpensive transition metals, is a promising cathode for sodium-ion batteries. The P3 phase as a covering layer in this composite shows not only in excellent electrochemical performance but also its tolerance to moisture. The results indicate that partial Zn substitutes can effectively control biphase formation for improving the structural/electrochemical stability as well as the ionic diffusion coefficient. Based on in situ synchrotron X-ray diffraction coupled with electron-energy-loss spectroscopy, a possible Cu^2+/3+ redox reaction mechanism has now been revealed.

Manganese based layered oxides with modulated electronic and thermodynamic properties for sodium ion batteries

Manganese based layered oxides have received increasing attention as cathode materials for sodium ion batteries due to their high theoretical capacities and good sodium ion conductivities. However, the Jahn–Teller distortion arising from the manganese (III) centers destabilizes the host structure and deteriorates the cycling life. Herein, we report that zinc-doped Na_0.833[Li_0.25Mn_0.75]O₂ can not only suppress the Jahn–Teller effect but also reduce the inherent phase separations. The reduction of manganese (III) amount in the zinc-doped sample, as predicted by first-principles calculations, has been confirmed by its high binding energies and the reduced octahedral structural variations. In the viewpoint of thermodynamics, the zinc-doped sample has lower formation energy, more stable ground states, and fewer spinodal decomposition regions than those of the undoped sample, all of which make it charge or discharge without any phase transition. Hence, the zinc-doped sample shows superior cycling performance, demonstrating that zinc doping is an effective strategy for developing high-performance layered cathode materials.

Mn-based layered oxides are promising cathode materials for next generation sodium ion batteries. To address two existing issues facing the system, here the authors show that a simple zinc doping can suppress both Jahn–Teller distortion and phase separation, enabling enhanced cycling performance.

All Carbon Dual Ion Batteries

Dual ion batteries based on Na⁺ and PF₆^- received considerable attention due to their high operating voltage and the abundant Na resources. Here, cheap and easily obtained graphite that served as a cathode material for dual ion battery delivered a very high average discharge platform (4.52 V vs Na⁺/Na) by using sodium hexafluorophosphate in propylene carbonate as electrolyte. Moreover, the all-carbon dual ion batteries with graphite as cathode and hard carbon as anode exhibited an ultrahigh discharge voltage of 4.3 V, and a reversible capacity of 62 mAh·g^-1 at 40 mA·g^-1. Phase changes have been investigated in detail through in situ X-ray diffraction and in situ Raman characterizations. The stable structure provides long life cycling performance, and the pseudocapacitance behavior also demonstrates its benefits to the rate capability. Thus, dual ion batteries based on sodium chemistry are very promising to find their applications in future.

An Alternative to Lithium Metal Anodes: Non-dendritic and Highly Reversible Sodium Metal Anodes for Li-Na Hybrid Batteries

Highly reversible, stable, and non-dendritic metal anode (Li, Na etc.) is a crucial requirement for next-generation high-energy batteries. Herein, we have built a Li-Na hybrid battery (LNHB) based on Na plating/stripping, which features a high and stable coulombic efficiency of 99.2 % after 100 cycles, low voltage hysteresis (42 mV at 2 mA cm^-2 ), and fast charge transfer. As a result of the Li⁺ electrostatic shield layer, the Na deposition showed cubic morphology rather than dendritic, even at high current density of 5 mA cm^-2 . The solvation/desolvation of Li⁺ and Na⁺ were modelled by density functional theory calculations, demonstrating the fast desolvation kinetics of Na⁺ . Owing to the superior performance of the Na metal anode, the LNHB coupled with LiFePO₄ cathode exhibited low voltage hysteresis and stable cycling performance that demonstrates its feasibility in practical applications.

Atomic cobalt as an efficient electrocatalyst in sulfur cathodes for superior room-temperature sodium-sulfur batteries

The low-cost room-temperature sodium-sulfur battery system is arousing extensive interest owing to its promise for large-scale applications. Although significant efforts have been made, resolving low sulfur reaction activity and severe polysulfide dissolution remains challenging. Here, a sulfur host comprised of atomic cobalt-decorated hollow carbon nanospheres is synthesized to enhance sulfur reactivity and to electrocatalytically reduce polysulfide into the final product, sodium sulfide. The constructed sulfur cathode delivers an initial reversible capacity of 1081 mA h g-1 with 64.7% sulfur utilization rate; significantly, the cell retained a high reversible capacity of 508 mA h g-1 at 100 mA g-1 after 600 cycles. An excellent rate capability is achieved with an average capacity of 220.3 mA h g-1 at the high current density of 5 A g-1. Moreover, the electrocatalytic effects of atomic cobalt are clearly evidenced by operando Raman spectroscopy, synchrotron X-ray diffraction, and density functional theory.

Novel Non-Carbon Sulfur Hosts Based on Strong Chemisorption for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are considered as promising candidates for energy storage systems owing to their high theoretical capacity and high energy density. The application of Li-S batteries is hindered by several obstacles, however, including the shuttle effect, poor electrical conductivity, and the severe volume expansion of sulfur. The traditional method is to integrate sulfur with carbon materials. But the interaction between polysulfide intermediates and carbon is only weak physical adsorption, which easily leads to the escape of species from the framework (shuttle effect) of the material causing capacity loss. Recently, however, there has been a trend for the introduction of novel non-carbon materials as sulfur hosts based on the strong chemisorption. This review highlights recent research progress on novel non-carbon sulfur hosts based on strong chemisorption, in Li-S batteries. In comparison with carbon-based sulfur hosts, most non-carbon sulfur hosts have been demonstrated to be polar host materials that could efficiently adsorb polysulfide via strong chemisorption, mitigating their dissolution. The intrinsic mechanism associated with the role of non-carbon-based host materials in improving the performance of Li-S batteries is discussed.

Research Progress in MnO2 -Carbon Based Supercapacitor Electrode Materials

With the serious impact of fossil fuels on the environment and the rapid development of the global economy, the development of clean and usable energy storage devices has become one of the most important themes of sustainable development in the world today. Supercapacitors are a new type of green energy storage device, with high power density, long cycle life, wide temperature range, and both economic and environmental advantages. In many industries, they have enormous application prospects. Electrode materials are an important factor affecting the performance of supercapacitors. MnO₂ -based materials are widely investigated for supercapacitors because of their high theoretical capacitance, good chemical stability, low cost, and environmental friendliness. To achieve high specific capacitance and high rate capability, the current best solution is to use MnO₂ and carbon composite materials. Herein, MnO₂ -carbon composite as supercapacitor electrode materials is reviewed including the synthesis method and research status in recent years. Finally, the challenges and future development directions of an MnO₂ -carbon based supercapacitor are summarized.

Nanocomposite Materials for the Sodium-Ion Battery: A Review

Clean energy has become an important topic in recent decades because of the serious global issues related to the development of energy, such as environmental contamination, and the intermittence of the traditional energy sources. Creating new battery-related energy storage facilities is an urgent subject for human beings to address and for solutions for the future. Compared with lithium-based batteries, sodium-ion batteries have become the new focal point in the competition for clean energy solutions and have more potential for commercialization due to the huge natural abundance of sodium. Nevertheless, sodium-ion batteries still exhibit some challenges, like inferior electrochemical performance caused by the bigger ionic size of Na⁺ ions, the detrimental volume expansion, and the low conductivity of the active materials. To solve these issues, nanocomposites have recently been applied as a new class of electrodes to enhance the electrochemical performance in sodium batteries based on advantages that include the size effect, high stability, and excellent conductivity. In this Review, the recent development of nanocomposite materials applied in sodium-ion batteries is summarized, and the existing challenges and the potential solutions are presented.

Ion selective separators based on graphene oxide for stabilizing lithium organic batteries

A thin bicomponent layer with GO and Super P enhances electroactive cathode material utilization for stable lithium organic batteries.

Advances and Challenges in Metal Sulfides/Selenides for Next-Generation Rechargeable Sodium-Ion Batteries

Rechargeable sodium-ion batteries (SIBs), as the most promising alternative to commercial lithium-ion batteries, have received tremendous attention during the last decade. Among all the anode materials for SIBs, metal sulfides/selenides (MXs) have shown inspiring results because of their versatile material species and high theoretical capacity. They suffer from large volume expansion, however, which leads to bad cycling performance. Thus, methods such as carbon modification, nanosize design, electrolyte optimization, and cut-off voltage control are used to obtain enhanced performance. Here, recent progress on MXs is summarized in terms of arranging the crystal structure, synthesis methods, electrochemical performance, mechanisms, and kinetics. Challenges are presented and effective ways to solve the problems are proposed, and a perspective for future material design is also given. It is hoped that light is shed on the development of MXs to help finally find applications for next-generation rechargeable batteries.

Carbon-Encapsulated Sn@N-Doped Carbon Nanotubes as Anode Materials for Application in SIBs

Carbon-encapsulated Sn@N-doped carbon tubes with submicron diameters were obtained via the simple reduction of C@SnO₂@N-doped carbon composites that were fabricated by a hydrothermal approach. Sn nanoparticles encapsulated in carbon layers were distributed uniformly on the surfaces of the N-doped carbon nanotubes. The electrochemical performances of the composites were systematically investigated as anode materials in sodium-ion batteries (SIBs). The composite electrode could attain a good reversible capacity of 398.4 mAh g^-1 when discharging at 100 mA g^-1, with capacity retention of 67.3% and very high Coulombic efficiency of 99.7% over 150 cycles. This good cycling performance, when compared to only 17.5 mAh g^-1 delivered by bare Sn particles prepared via the same method without the presence of N-doped carbon, could be mainly ascribed to the uniform distribution of the precursor SnO₂ on the substrate of N-doped carbon tubes with three-dimensional structure, which provides more reaction sites to reduce the diffusion distance of Na⁺, further facilitating Na⁺-ion diffusion and relieves the huge volume expansion during charging/discharging. These outcomes imply that such a Sn/C composite would provide more options as an anode candidate for SIBs.

Few Atomic Layered Lithium Cathode Materials to Achieve Ultrahigh Rate Capability in Lithium-Ion Batteries

The most promising cathode materials, including LiCoO₂ (layered), LiMn₂ O₄ (spinel), and LiFePO₄ (olivine), have been the focus of intense research to develop rechargeable lithium-ion batteries (LIBs) for portable electronic devices. Sluggish lithium diffusion, however, and unsatisfactory long-term cycling performance still limit the development of present LIBs for several applications, such as plug-in/hybrid electric vehicles. Motivated by the success of graphene and novel 2D materials with unique physical and chemical properties, herein, a simple shear-assisted mechanical exfoliation method to synthesize few-layered nanosheets of LiCoO₂ , LiMn₂ O₄ , and LiFePO₄ is used. Importantly, these as-prepared nanosheets with preferred orientations and optimized stable structures exhibit excellent C-rate capability and long-term cycling performance with much reduced volume expansion during cycling. In particular, the zero-strain insertion phenomenon could be achieved in 2-3 such layers of LiCoO₂ electrode materials, which could open up a new way to the further development of next-generation long-life and high-rate batteries.

In Situ Grown S Nanosheets on Cu Foam: An Ultrahigh Electroactive Cathode for Room-Temperature Na-S Batteries

Room-temperature sodium-sulfur batteries are competitive candidates for large-scale stationary energy storage because of their low price and high theoretical capacity. Herein, pure S nanosheet cathodes can be grown in situ on three-dimensional Cu foam substrate with the condensation between binary polymeric binders, serving as a model system to investigate the formation and electrochemical mechanism of unique S nanosheets on the Cu current collectors. On the basis of the confirmed conversion reactions to Na₂S, The constructed cathode exhibits ultrahigh initial discharge/charge capacity of 3189/1403 mAh g^-1. These results suggest that there is great potential to optimize S cathode by exploiting low-cost Cu substrates instead of conventional Al current collectors.

Carbon-Coated Na3.32 Fe2.34 (P2 O7 )2 Cathode Material for High-Rate and Long-Life Sodium-Ion Batteries

Rechargeable sodium-ion batteries are proposed as the most appropriate alternative to lithium batteries due to the fast consumption of the limited lithium resources. Due to their improved safety, polyanion framework compounds have recently gained attention as potential candidates. With the earth-abundant element Fe being the redox center, the uniform carbon-coated Na_3.32 Fe_2.34 (P₂ O₇ )₂ /C composite represents a promising alternative for sodium-ion batteries. The electrochemical results show that the as-prepared Na_3.32 Fe_2.34 (P₂ O₇ )₂ /C composite can deliver capacity of ≈100 mA h g^-1 at 0.1 C (1 C = 120 mA g^-1 ), with capacity retention of 92.3% at 0.5 C after 300 cycles. After adding fluoroethylene carbonate additive to the electrolyte, 89.6% of the initial capacity is maintained, even after 1100 cycles at 5 C. The electrochemical mechanism is systematically investigated via both in situ synchrotron X-ray diffraction and density functional theory calculations. The results show that the sodiation and desodiation are single-phase-transition processes with two 1D sodium paths, which facilitates fast ionic diffusion. A small volume change, nearly 100% first-cycle Coulombic efficiency, and a pseudocapacitance contribution are also demonstrated. This research indicates that this new compound could be a potential competitor for other iron-based cathode electrodes for application in large-scale Na rechargeable batteries.

Silicon/Mesoporous Carbon/Crystalline TiO2 Nanoparticles for Highly Stable Lithium Storage

A core-shell-shell heterostructure of Si nanoparticles as the core with mesoporous carbon and crystalline TiO₂ as the double shells (Si@C@TiO₂) is utilized as an anode material for lithium-ion batteries, which could successfully tackle the vital setbacks of Si anode materials, in terms of intrinsic low conductivity, unstable solid-electrolyte interphase (SEI) films, and serious volume variations. Combined with the high theoretical capacity of the Si core (4200 mA h g^-1), the double shells can perfectly avoid direct contact of Si with electrolyte, leading to stable SEI films and enhanced Coulombic efficiency. On the other hand, the carbon inner shell is effective at improving the overall conductivity of the Si-based electrode; the TiO₂ outer shell is expected to serve as a rigid layer to achieve high structural stability and integrity of the core-shell-shell structure. As a result, the elaborate Si@C@TiO₂ core-shell-shell nanoparticles are proven to show excellent Li storage properties. It delivers high reversible capacity of 1726 mA h g^-1 over 100 cycles, with outstanding cyclability of 1010 mA h g^-1 even after 710 cycles.

Silicon/Mesoporous Carbon/Crystalline TiO2 Nanoparticles for Highly Stable Lithium Storage

A core-shell-shell heterostructure of Si nanoparticles as the core with mesoporous carbon and crystalline TiO₂ as the double shells (Si@C@TiO₂) is utilized as an anode material for lithium-ion batteries, which could successfully tackle the vital setbacks of Si anode materials, in terms of intrinsic low conductivity, unstable solid-electrolyte interphase (SEI) films, and serious volume variations. Combined with the high theoretical capacity of the Si core (4200 mA h g^-1), the double shells can perfectly avoid direct contact of Si with electrolyte, leading to stable SEI films and enhanced Coulombic efficiency. On the other hand, the carbon inner shell is effective at improving the overall conductivity of the Si-based electrode; the TiO₂ outer shell is expected to serve as a rigid layer to achieve high structural stability and integrity of the core-shell-shell structure. As a result, the elaborate Si@C@TiO₂ core-shell-shell nanoparticles are proven to show excellent Li storage properties. It delivers high reversible capacity of 1726 mA h g^-1 over 100 cycles, with outstanding cyclability of 1010 mA h g^-1 even after 710 cycles.

Ultrafine Mn3O4 Nanowires/Three-Dimensional Graphene/Single-Walled Carbon Nanotube Composites: Superior Electrocatalysts for Oxygen Reduction and Enhanced Mg/Air Batteries

The exploration of highly efficient catalysts for the oxygen reduction reaction to improve sluggish kinetics still remains a great challenge for advanced energy conversion and storage in metal/air batteries. In this work, ultrafine Mn₃O₄ nanowires/three-dimensional graphene/single-walled carbon nanotube catalysts with an electron transfer number of 3.95 (at 0.60 V vs Ag/AgCl) and kinetic current density of 21.7-28.8 mA cm^-2 were developed via a microwave-irradiation-assisted hexadecyl trimethylammonium bromide (CTAB) surfactant procedure to greatly enhance the overall catalytic performance in Mg/air batteries. To match the electrochemical activity of the cathode catalysts, a large-scale Mg anode prepared with micropersimmon-like particles via a mechanical disintegrator and Mg(NO₃)₂-NaNO₂-based electrolyte containing 1.0 wt % trihexyl(tetradecyl)phosphonium chloride ionic liquid were applied. Combining the ultrafine Mn₃O₄ nanowires/three-dimensional graphene/single-walled carbon nanotube as an efficient electrocatalyst for the oxygen reduction reaction and an Mg micro-/nanoscale anode in the novel electrolyte, the advanced Mg/air batteries demonstrated a high cell open circuit voltage (1.49 V), a high plateau voltage (1.34 V), and a long discharge time (4177 min) at 0.2 mA cm^-1, showing a high energy density. Therefore, it is believed that this device configuration has great potential for application in new energy storage technologies.

Understanding Performance Differences from Various Synthesis Methods: A Case Study of Spinel LiCr0.2Ni0.4Mn1.4O4 Cathode Material

High voltage (5-V class) spinel LiCr_0.2Ni_0.4Mn_1.4O₄ is one of the most promising cathode materials to meet the energy requirements of lithium-ion batteries for electric vehicles and hybrid electric vehicles. For the mass production of this material (1 kg or higher), different synthesis routes will lead to different electrochemical performances, even with similar morphology and similar crystal structure obtained from laboratory X-ray diffraction, and the reason for this issue is still not clear. Herein, we have investigated the reasons for the different electrochemical performances resulting from three common synthesis routes (spray pyrolysis, coprecipitation, and sol-gel). Taking advantage of the high-resolution X-ray beam in synchrotron X-ray diffraction, we find that varying phase composition and the generated impurities, rather than the particle distribution, are likely to be the main reasons for the detected electrochemical variations. A higher amount of impurities will result in greater charge transfer resistance, inferior cycling stability, and more oxygen/lithium vacancies. Therefore, it is very important to obtain a deeper understanding with the help of higher-resolution X-rays and to provide better guidance for mass production of this cathode material for practical applications.

Effects of Carbon Content on the Electrochemical Performances of MoS2-C Nanocomposites for Li-Ion Batteries

Molybdenum disulfide is popular for rechargeable batteries, especially in Li-ion batteries, because of its layered structure and relatively high specific capacity. In this paper, we report MoS2-C nanocomposites that are synthesized by a hydrothermal process, and their use as anode material for Li-ion batteries. Ascorbic acid is used as the carbon source, and the carbon contents can be tuned from 2.5 wt % to 16.2 wt %. With increasing of carbon content, the morphology of MoS2-C nanocomposites changes from nanoflowers to nanospheres, and the particle size is decreased from 200 to 60 nm. This change is caused by the chemical complex interaction of ascorbic acid. The MoS2-C nanocomposite with 8.4 wt % C features a high capacity of 970 mAh g(-1) and sustains a capacity retention ratio of nearly 100% after 100 cycles. When the current increases to 1000 mA g(-1), the capacity still reaches 730 mAh g(-1). The above manifests that the carbon coating layer does not only accelerate the charge transfer kinetics to supply quick discharging and charging, but also hold the integrity of the electrode materials as evidenced by the long cycling stability. Therefore, MoS2-based nanocomposites could be used as commercial anode materials in Li-ion batteries.

Nanoengineering to Achieve High Sodium Storage: A Case Study of Carbon Coated Hierarchical Nanoporous TiO2 Microfibers

Nanoengineering of electrode materials can directly facilitate sodium ion accessibility and transport, thus enhancing electrochemical performance in sodium ion batteries. Here, highly sodium-accessible carbon coated nanoporous TiO₂ microfibers have been synthesised via the facile electrospinning technique which can deliver an enhanced capacity of ≈167 mAh g^-1 after 450 cycles at current density of 50 mA g^-1 and retain a capacity of ≈71 mAh g^-1 at the high current rate of 1 A g^-1. With the benefits of their porous structure, thin TiO₂ inner walls, and the introduction of conductive carbon, the nanoporous TiO₂/C microfibers exhibit high ion accessibility, fast Na ion transport, and fast electron transport, thereby leading to the excellent Na-storage properties presented here. Nanostructuring is proven to be a fruitful strategy that can alleviate the reliance on materials' intrinsic nature; and the electrospinning technique is versatile and cost-effective for the fabrication of such an effective nanoporous microfiber structure.

Binder-Free and Carbon-Free 3D Porous Air Electrode for Li-O2 Batteries with High Efficiency, High Capacity, and Long Life

Pt-Gd alloy polycrystalline thin film is deposited on 3D nickel foam by pulsed laser deposition method serving as a whole binder/carbon-free air electrode, showing great catalytic activity enhancement as an efficient bifunctional catalyst for the oxygen reduction and evolution reactions in lithium oxygen batteries. The porous structure can facilitate rapid O2 and electrolyte diffusion, as well as forming a continuous conductive network throughout the whole energy conversion process. It shows a favorable cycle performance in the full discharge/charge model, owing to the high catalytic activity of the Pt-Gd alloy composite and 3D porous nickel foam structure. Specially, excellent cycling performance under capacity limited mode is also demonstrated, in which the terminal discharge voltage is higher than 2.5 V and the terminal charge voltage is lower than 3.7 V after 100 cycles at a current density of 0.1 mA cm(-2) . Therefore, this electrocatalyst is a promising bifunctional electrocatalyst for lithium oxygen batteries and this depositing high-efficient electrocatalyst on porous substrate with polycrystalline thin film by pulsed laser deposition is also a promising technique in the future lithium oxygen batteries research.

Heteroaromatic organic compound with conjugated multi-carbonyl as cathode material for rechargeable lithium batteries

The heteroaromatic organic compound, N,N’-diphenyl-1,4,5,8-naphthalenetetra- carboxylic diimide (DP-NTCDI-250) as the cathode material of lithium batteries is prepared through a simple one-pot N-acylation reaction of 1,4,5,8-naphthalenetetra-carboxylic dianhydride (NTCDA) with phenylamine (PA) in DMF solution followed by heat treatment in 250 °C. The as prepared sample is characterized by the combination of elemental analysis, NMR, FT-IR, TGA, XRD, SEM and TEM. The electrochemical measurements show that DP-NTCDI-250 can deliver an initial discharge capacity of 170 mAh g⁻¹ at the current density of 25 mA g⁻¹. The capacity of 119 mAh g⁻¹ can be retained after 100 cycles. Even at the high current density of 500 mA g⁻¹, its capacity still reaches 105 mAh g⁻¹, indicating its high rate capability. Therefore, the as-prepared DP-NTCDI-250 could be a promising candidate as low cost cathode materials for lithium batteries.

Improved cycling stability of lithium–sulphur batteries by enhancing the retention of active material with a sandwiched hydrothermally treated graphite film

A new lithium–sulphur battery with a hydrothermally treated graphite film sandwiched between the separator and the sulphur cathode shows increased capacity, enhanced cycling stability and improved coulombic efficiency.

MoS2 with an intercalation reaction as a long-life anode material for lithium ion batteries

MoS₂ without carbon modification has achieved a long cycling performance by cutting off the terminal discharge voltage to preserve a layered structure.

Graphite-Nanoplate-Coated Bi2 S3 Composite with High-Volume Energy Density and Excellent Cycle Life for Room-Temperature Sodium-Sulfide Batteries

Graphite-nanoplate-coated Bi2 S3 composite (Bi2 S3 @C) has been prepared by a simple, scalable, and energy-efficient precipitation method combined with ball milling. The Bi2 S3 @C composite was used as the cathode material for sodium-sulfide batteries. It delivered an initial capacity of 550 mAh g(-1) and high stable specific energy in the range of 275-300 Wh kg(-1) at 0.1 C, with an enhanced capacity retention of 69 % over 100 cycles. The unique structure demonstrates superior cycling stability, with a capacity drop of 0.3 % per cycle over 100 cycles, compared with that of bare Bi2 S3 . The sodium storage mechanism of Bi2 S3 was investigated based on ex situ X-ray diffraction and scanning transmission electron microscopy.

Porous AgPd-Pd Composite Nanotubes as Highly Efficient Electrocatalysts for Lithium-Oxygen Batteries

Porous AgPd-Pd composite nanotubes (NTs) are used as an efficient bifunctional catalyst for the oxygen reduction and evolution reactions in lithium-oxygen batteries. The porous NT structure can facilitate rapid O2 and electrolyte diffusion through the NTs and provide abundant catalytic sites, forming a continuous conductive network throughout the entire energy conversion process, with excellent cycling performance.

Uniform yolk-shell iron sulfide-carbon nanospheres for superior sodium-iron sulfide batteries

Sodium–metal sulfide battery holds great promise for sustainable and cost-effective applications. Nevertheless, achieving high capacity and cycling stability remains a great challenge. Here, uniform yolk-shell iron sulfide–carbon nanospheres have been synthesized as cathode materials for the emerging sodium sulfide battery to achieve remarkable capacity of ∼545 mA h g⁻¹ over 100 cycles at 0.2 C (100 mA g⁻¹), delivering ultrahigh energy density of ∼438 Wh kg⁻¹. The proven conversion reaction between sodium and iron sulfide results in high capacity but severe volume changes. Nanostructural design, including of nanosized iron sulfide yolks (∼170 nm) with porous carbon shells (∼30 nm) and extra void space (∼20 nm) in between, has been used to achieve excellent cycling performance without sacrificing capacity. This sustainable sodium–iron sulfide battery is a promising candidate for stationary energy storage. Furthermore, this spatially confined sulfuration strategy offers a general method for other yolk-shell metal sulfide–carbon composites.

There is intensive research into the development of sodium–metal sulfide batteries. Here, the authors report a yolk-shell-like iron sulfide–carbon nanosphere structure as the cathode material which displays exceptionally high performance.

A Metal-Free, Free-Standing, Macroporous Graphene@g-C₃N₄ Composite Air Electrode for High-Energy Lithium Oxygen Batteries

The nonaqueous lithium oxygen battery is a promising candidate as a next-generation energy storage system because of its potentially high energy density (up to 2-3 kW kg(-1)), exceeding that of any other existing energy storage system for storing sustainable and clean energy to reduce greenhouse gas emissions and the consumption of nonrenewable fossil fuels. To achieve high energy density, long cycling stability, and low cost, the air electrode structure and the electrocatalysts play important roles. Here, a metal-free, free-standing macroporous graphene@graphitic carbon nitride (g-C3N4) composite air cathode is first reported, in which the g-C3N4 nanosheets can act as efficient electrocatalysts, and the macroporous graphene nanosheets can provide space for Li2O2 to deposit and also promote the electron transfer. The electrochemical results on the graphene@g-C3N4 composite air electrode show a 0.48 V lower charging plateau and a 0.13 V higher discharging plateau than those of pure graphene air electrode, with a discharge capacity of nearly 17300 mA h g(-1)(composite) . Excellent cycling performance, with terminal voltage higher than 2.4 V after 105 cycles at 1000 mA h g(-1)(composite) capacity, can also be achieved. Therefore, this hybrid material is a promising candidate for use as a high energy, long-cycle-life, and low-cost cathode material for lithium oxygen batteries.