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Lithium-sulfur (Li-S) batteries are regarded as one of the promising candidates for the next-generation energy storage system owing to their high capacity and energy density. However, the durable operation for the batteries is blocked by the shuttle behavior of soluble lithium polysulfides and the sluggish kinetics in the redox process. Here, VN nanoparticles on nitrogen-doped graphene (VN/NG) composite is synthesized by simple calcining method to modify the separators, which can not only chemically trap polysulfides, but also catalyze the conversion reaction between the polysulfides and the insoluble Li2S during the charge/discharge process. The catalytic effects of VN/NG are verified by the calculated activation energy (Ea), which is smaller than the counterpart with NG toward both directions of redox. Because of the synergistic adsorption-catalysis of VN/NG, the cells with VN/NG-modified separators deliver a superior rate performance (791 mAh g−1 at 5C) and cycling stability (863 mAh g−1 after 300 cycles with a low decaying rate of 0.068% per loop at 1C). This work provides a simple preparation strategy and fundamental understanding of the bifunctional catalyst for high-performance Li-S batteries.

Considering the abundance of iron and manganese within the Earth's crust, the cathode O3-NaFe0.5Mn0.5O2 has shown great potential for large-scale energy storage. Following the strategy of introducing specific heteroelements to optimize the structural stability for energy storage, the work has obtained an O3-type NaFe0.4Mn0.49Cu0.1Zr0.01O2 that exhibits enhanced electrochemical performance and air stability. It displays an initial reversible capacity of 147.5 mAh g-1 at 0.1C between 2 and 4.1 V, a capacity retention ratio exceeding 69.6% after 100 cycles at 0.2C, and a discharge capacity of 70.8 mAh g-1 at a high rate of 5C, which is superior to that of O3-NaFe0.5Mn0.5O2. The codoping of Cu/Zr reserves the layered O3 structure and enlarges the interlayer spacing, promoting the diffusion of Na+. In addition, the structural stability and air stability observed by Cu-doping is well maintained via the incorporation of extra Zr favoring a highly reversible phase conversion process. Thus, this work has demonstrated an efficient strategy for developing cobalt/nickel-free high-capacity and air-stable cathodes for sodium-ion batteries.

Sodium-ion batteries (SIBs) are recognized as attractive alternatives for grid-scale electrochemical energy storage applications. Transition metal oxide cathodes represent one of the most dynamic materials for industrialization among the various cathodes for SIBs. Here, a cation-doped cathode Na

Tremendous effort has been devoted to develop durable electrode materials for sodium ion batteries. This work focuses on enhancing the reversibility of a cathode material Na0.5Ni0.25Mn0.75O2 by adopting the titanium cation doping strategy. The obtained P2-Na0.5Ni0.25Mn0.60Ti0.15O2 material shows smooth charge–discharge curves upon suppressing the Na+/vacancy ordering effect via the partial substitution of Mn4+ for Ti4+, and enhanced cycling performance. It exhibits a reversible capacity of 138 mA h g−1 at 0.5C, as well as a high rate capacity of 81 mA h g−1 at 5C between a cut-off voltage of 2 and 4 V, while long-term cycling stability is demonstrated with a capacity retention of 84% over 200 cycles. An enhanced cycling stability is also observed when the voltage is between 2 and 4.2 V. The feasibility of constructing a symmetrical Na-ion full cell with Na0.5Ni0.25Mn0.60Ti0.15O2 as cathode and anode electrodes is also demonstrated. The titanium cation doping results in reduced charge transfer impedance and an enhanced sodium cation diffusion coefficient, thus suggesting an efficient strategy to obtain a durable cathode material for sodium ion batteries.

A freestanding thin-film composite with carbon nanotubes/carbon fiber modified by sulfur (S-CNTs/CF) has been fabricated by chemical vapor deposition (CVD) method as the binder-free cathode for lithium sulfur battery. This porous electronic conductor with 3D structure improved the electrochemical performance of the cathodes by simultaneously increasing porosity of material and changing conductive pathway. Electrochemical test results showed that the discharge specific capacity of S-CNTs/CF positive electrode decreased slightly from initial 1213.6 mAh g−1(Sulfur) to 798.4 mAh g−1(Sulfur) after 55 cycles. Comparing with powder cathode, the electrochemical performance of S-CNTs/CF cell is improved significantly. It proves that establishing a sulfur electrode with stable conductive and high porous structure provide a promising way to improve the cycle life.

Anion-doping strategy represents one efficient route to adjust the structure of electrode material for advanced reversible batteries. The work herein obtains an optimized F-doping sodium manganese oxide Na0.44MnO1.93F0.07 with a layer-tunnel hybrid structure, and the essential factors such as synthesis temperature and crystal structure which determine the electrochemical behavior for the F-doping cathode materials are systematically explored and investigated. The optimized cathode Na0.44MnO1.93F0.07 prepared at 900 °C for 3 h, among various Na0.44MnO2−xFx samples, delivers an extraordinary discharge capacity of 149 mA h g−1 and 138 mA h g−1 at 0.5 C and 1 C, respectively. In addition, the electrode displays an impressive cycling stability with a superb capacity retention rate of approximately 79% over 400 cycles at 5 C. And thus, it shows enhanced reversible capacity over the tunnel phase Na0.44MnO2. Therefore, this work provides a new avenue for designing and optimizing the advanced cathode materials with superior electrochemical performance for sodium-ion batteries by introducing halogen anions to modify the structure.

Sodium-ion batteries (SIBs) have drawn more attention to serve as one of the promising energy storage devices owing to the abundance of sodium resources and similar characters with lithium element. Hard carbon materials derived from biomass or biomass waste have been considered to act as candidate anode materials for SIBs. In this paper, we have successfully prepared curly hard carbon materials using pistachio shells as biomass template via a two-step approach including hydrothermal treatment and following a pyrolysis process at various temperatures. Physical properties of pistachio shell-derived hard carbons (PSHCs) including microstructure, morphology and pore size distribution are evaluated by X-ray diffraction, Raman spectrum and N2 sorption analysis. The PSHCs carbonized at 1000 °C (PSHC-1000) with average micropores of 0.7398 nm and larger interlayer space of the (002) crystal plane deliver the highest reversible capacity of 317 mAh g−1 at 0.1C, also show the excellent long-term cycling and rate performances. Electrochemical impedance spectroscopy technology is introduced to study the kinetics parameters during the first sodiation process of PSHC-1000 electrode, and also to compare the resistance of the charge transfer process for all the PSHCs. Results exhibit PSHC-1000 electrode with the symmetry factor of 0.1352 has the smallest charge transfer resistance, leading to more easily transportation of electrons and ions. This work can provide a simple and green route for preparation of hard carbon materials derived from biomass waste with unique morphology and microstructure which can exhibit an excellent electrochemical performance.

For supercapacitors, pores in electrode materials can accelerate chemical reaction kinetics by shortening ion diffusion distances and by enlarging electrolyte/electrode interfaces. This article describes a simple one-step route for the preparation of pure-phase porous Ni3(NO3)2(OH)4 nano-sheets by directly heating a mild Ni(NO3)2 and urea solution. During heating, urea decomposed into NH3·H2O, which provided a suitable alkaline environment for the formation of Ni3(NO3)2(OH)4 nano-sheets. Meanwhile, the side product, NH4NO3, created numerous pores as a pore-forming agent. After NH4NO3 removal, the specific surface areas and pore volumes of products were boosted by ∼180-times (from 0.61 to 113.12 m2/g) and ∼90-times (from 3.40 × 10−3 to 3.17 × 10−1 m2/g), respectively. As a cathode material of supercapacitor, the porous Ni3(NO3)2(OH)4 nano-sheets exhibited a high specific capacitance of 1094 F/g at an ultrahigh mass loading of 17.55 mg/cm2, leading to an impressive areal capacitance of 19.2 F/cm2. Furthermore, a Ni3(NO3)2(OH)4 nano-sheet//commercial active carbon asymmetric supercapacitor was constructed and delivered an energy density of 33.2 Wh/Kg at a power density of 190.5 W/Kg, based on the mass of active materials on both electrodes.

O3-type transition metal oxides as the cathodes for Na-ion batteries have attracted extensive attention owing to their high theoretical specific capacity and ease of synthesis. This work indicates enhanced electrochemical reversibility and improved air stability via a rational Zn2+ doping for O3-NaNi0.5Mn0.5O2. It exhibits a discharge capacity of 113 mAh g−1 at 0.5 C, excellent capacity retention of 80% after 150 cycles, and the capability to release a capacity of 82 mAh g−1 at 5 C in the voltage range of 2–4 V. The doped cathode undergoes a phase transition of O3-O3/O′3-P3-P′3-O''3 with a small volume change of approximately 2.00% in the voltage range of 2–4 V, and a subsequent slight structural change in the high voltage range of 4–4.2 V, which well demonstrates the enhanced cyclic stability. The assembled full cell confirms the feasibility of applying O3-type NaNi0.47Zn0.03Mn0.5O2 cathode for Na-ion batteries. Thus, the work suggests an efficient strategy to better release the potential of high-energy cathode for Na-ion batteries.

Na0.44MnO2 has aroused global interest as a promising cathode material for sodium ion batteries due to its unique tunnel structure. Rod-like Na0.44MnO2 is synthesized here via a simple, fast and environment-friendly oxalate precursor-based process, and the electrochemical performances, as well as the structural evolution within the electrode redox process and the chemical mechanism for material synthesis, are systematically investigated. The Na0.44MnO2 material prepared at 900 °C for 3 h (denoted as NMO-9003) possesses the highest reversible capacity of 120 mAh g−1 at 0.2 C and an optimal rate capacity of 106 mAh g−1 at 1 C, while its long-term capacity retention is 86% after 500 cycles at 20 C, indicating superior structural reversibility. In addition, the NMO-9003 sample shows the fastest cationic diffusion rate at approximately 1.2 × 10−13 cm2 s−1. The density functional theory (DFT)-based calculation is adopted to explore the lattice variation of Na0.44MnO2 upon the electrode process, which confirms that the host structure bears a minor volume change approximately 7% from 2.0 to 3.8 V, well demonstrating the origin of excellent reversibility.

The oxygen evolution reaction (OER) is considered the bottleneck for the water-splitting process, due to its high activation barrier. Therefore, developing efficient and low-cost electrocatalysts to enhance sluggish kinetics remains a challenge. As an admittedly promising candidate catalyst for the OER, layered double hydroxides (LDHs) are limited by weak conductivity and poor activity sites. Herein, an interface engineering strategy was utilized to increase the intrinsic activity of CoV-LDHs by coupling with FeOOH via a novel and inexpensive protocol. The hybrid catalyst CoV-LDHs@FeOOH/NF showed a low overpotential of 232 mV at a current density of 10 mA cm −2, with a low Tafel slope of 16.7 mV dec−1 in a 1 M KOH aqueous solution, which is superior to that obtained for the individual CoV-LDHs/NF and FeOOH/NF counterparts. The enhanced OER activity mainly benefits from the electronic exchange among Co2+, V3+, and Fe3+ . In addition, the heterostructure shows excellent catalytic durability of approximately 100 h. This work provides a novel method to synthesize V-based LDH materials and an excellent electrocatalyst for improving OER activity.

A high and stable reversible specific capacity (1277.7 mAh g−1) was successfully achieved by the CoFe2O4/ordered mesoporous carbon nanohybrids (CFO/CMK-3) composite anode at the current density of 0.1 A g−1 after 100 cycles. CFO/CMK-3 electrode also exhibited a stable capacity up to 733.2 and 482.6 mAh g−1 at the current densities of 0.5 and 1 A g−1 after 500 cycles, respectively. The CFO particles were found to be uniformly distributed inside the pore channels of CMK-3. Structure characterization before and after 100 tests revealed that the specific CMK-3 mesoporous structure and CFO crystallites remained unchanged. The stability of the anode composite stability and the rapid redox capability of CFO gave rise to superior lithium storage capacity and excellent cycling stability. CFO/CMK-3 showed a great promise to serve as anode for high-performance lithium-ion battery.

The shuttle effect of soluble intermediate polysulfide toward lithium anode, the sluggish redox kinetics of polysulfides conversion and the low lithium ion/electrical conductivity severely limited the commercialization of lithium-sulfur (Li-S) battery. To overcome the bottleneck, herein we designed a Nickel foam/graphene/sulfonated carbon nanotubes (NG/CNTs-SO3−) three-dimensional (3D) interconnected electrode. Nickel foam weaved with 1D multi-wall carbon nanotubes (MWCNT) and 2D graphene (named as NG/CNTs) is used as the host for sulfur accommodation, forming a continuously ion-electronic conductive 3D network and boosting fast redox reaction kinetic. Moreover, the negatively charged –SO3− groups transform the cathode surface from hydrophobic to hydrophilic, and it not only acts as constructing ion-selective layer for suppressing the shuttle effect of polysulfides, but also accelerates the polysulfides conversion process by strong adsorption sites to anchor polysulfides. In addition, the grafted –SO3− groups reinforce the rapid transportation of lithium-ion five times than none negatively charged groups decorated ones. The Li-S batteries with NG/CNTs-SO3− cathode delivers an initial capacity of 1380 mAh g−1 at 0.2 C, retaining a capacity of 1043.5 mAh g−1 after 100 cycles. Furthermore, the cells with NG/CNTs-SO3− cathode also exhibits excellent cycling stability with capacity decay of 0.031% at 2 C and rate capability, which confirms it is outstanding to improve the electrochemical performance and inhibit the shuttle effect.

Si/C composites of carbon hollow structures loaded with Si nanoparticles (NPs) (Si/C-HSs) were prepared by one-step pyrolysis of a mixture of Si NPs and expandable microspheres (EMs). For the Si/C-HSs, hollow carbon shells with rough surfaces were formed by directly carbonizing the polymer shells of EMs, and the Si NPs fell into the void space or were loaded on the rough surfaces of the carbon shells. The EM-based carbon shells accommodated the volume expansion of the Si NPs and improved the electrical conductivity of the composites. As a result, the Si/C-HSs exhibited a high capacity (initial reversible capacity: 854.4 mAh g−1 at 300 mA g−1), stable cycling performance (capacity retention: 80% after 50 cycles), and excellent rate capability. Keywords: Expandable microsphere, Si/C composite, Hollow structure, Anode, Lithium ion battery

Potassium-ion batteries (KIBs) have been recognized as one promising type of new energy storage technology. Exploring and developing novel and effective cathode materials has become the hotspot research area. Herein, a layered K0.48Ni0.2Co0.2Mn0.6O2 (KNCMO) with a mixed morphology of microspheres and microcubes was prepared. When evaluated for use in KIBs, the KNCMO exhibited outstanding electrochemical properties. In practical terms, KNCMO can deliver a reversible capacity of ~57 mAh g−1 at 40 mA g−1, and shows good rate performance. When the specific current was increased to 400 mA g−1, a considerable reversible capacity of ~35 mAh g−1 after 350 cycles can be obtained. This work can serve as a broader insight into the future development of cathode materials for potassium-ion batteries.

The development of suitable cathode materials for sodium-ion batteries is the key issue to realize their large-scale applications owing to the lack of appropriate materials with adequate electrochemical capacity and reversibility for Na-ion insertion reaction. Here, a string of nickel hexacyanoferrate (NiHCF) nanocubes is coaxially grown on a CNT@bipolar conducting polymer (BCP) by a facile electrochemical route, and used as a high-performance cathode material for sodium-ion batteries. The obtained cathode shows a surprisingly high specific capacity of 194 mA h g-1 upon the initial discharge, a good cycling performance and excellent rate performance. It is considered that the unique nanostructure not only effectively facilitates the electrode/electrolyte interaction and the electronic and ionic transportation but also exerts a synergistic effect between the BCP and NiHCF nanocubes to trigger the kinetics of the electron and ion transport. It is expected that such a promising environmentally friendly alternative cathode material can be widely applied for sodium-ion batteries (SIBs).

This Letter describes a simple molten salt approach to the synthesis of K 2 Mo 4 O 13 nanobelts with lengths of several tens of micrometres. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectrum and energy dispersive spectroscopy are used to characterise the structure, morphology and composition of the sample. The UV-visible spectrum shows that the bandgap of the K 2 Mo 4 O 13 nanobelts is 3.6 eV. Photoluminescence measurement shows a strong and broad emission peak of 355 nm for the K 2 Mo 4 O 13 nanobelts. Electrochemical tests show good performance of the material in cycling stability as cathode material for Li-ion batteries.