NiCo2O4 nanosheets and nanocones as additive-free anodes for high-performance Li-ion batteries

Development of novel electrode materials with high energy and power densities for lithium-ion batteries (LIBs) is the key to meet the demands of electric vehicles. Transition metal oxides that can react with large amounts of Li⁺ for electrochemical energy storage are considered promising anode materials for LIBs. In this work, NiCo₂O₄ nanosheets and nanocones on Ni foam have been synthesized via general hydrothermal growth and low-temperature annealing treatment. They exhibit high rate capacities and good cyclic performance as LIB anodes owing to their architecture design, which reduces ion and electron transport distance, expands the electrode–electrolyte contact, increases the structural stability, and buffers volume change during cycles. Notably, NiCo₂O₄ nanosheets deliver an initial capacity of 2239 mAh g⁻¹ and a rate capacity of 964 mAh g⁻¹ at current densities of 100 and 5000 mA g⁻¹, respectively. The corresponding values of nanocones are 1912 and 714 mAh g⁻¹. Hence, the as-synthesized NiCo₂O₄ nanosheets and nanocones, which are carbon-free and binder-free with higher energy densities and stronger connections between active materials and current collectors for better stability, are promising for use in advanced anodes for high-performance LIBs.     

Reduced graphene oxide with superior cycling stability and rate capability for sodium storage

Sodium ion battery is a promising electrical energy storage system for sustainable energy storage applications due to the abundance of sodium resources and their low cost. In this communication, the electrochemical properties of sodium ion storage in reduced graphene oxide (RGO) were studied in an electrolyte consisting of 1 M NaClO₄ in propylene carbonate (PC). The experimental results show that the RGO anode allowed significant sodium ion insertion, leading to higher capacity at high current density compared to the previously reported results for carbon materials. This is due to the fact that RGO possesses higher electrical conductivity and is a more active host, with large interlayer distances and a disordered structure, enabling it to store a higher amount of Na ions. RGO anode exhibits high capacity combined with long-term cycling stability at high current densities, leading to reversible capacity as high as 174.3 mAh g⁻¹ at 0.2 C (40 mA g⁻¹), and even 93.3 mAh g⁻¹ at 1 C (200 mA g⁻¹) after 250 cycles. Furthermore, RGO could yield a high capacity of 141 mAh g⁻¹ at 0.2 C (40 mA g⁻¹) over 1000 cycles.     

A nest-like hierarchical porous V2O5 as a high-performance cathode material for Li-ion batteries

In this article, V₂O₅ with a novel nest-like hierarchical porous structure has been synthesized by a facile solvothermal method and investigated as cathode material for lithium-ion batteries. The nest-like V₂O₅ with a diameter of about 1.5 µm, was composed of interconnected nanosheets with a highly porous structure. Without other modification, the as-prepared V₂O₅ electrode exhibited superior capacity. An initial discharge capacity of 330 mAh g⁻¹ (at a current density of 100 mA g⁻¹) could be delivered and a stable discharge capacity of 240 mAh g⁻¹ after 50 cycles is maintained. The excellent performance was attributed to the hierarchical porous structure that could buffer against the local volume change and shorten the lithium-ions diffusion distance.     

Bamboo-like amorphous carbon nanotubes clad in ultrathin nickel oxide nanosheets for lithium-ion battery electrodes with long cycle life

In this work, we report the synthesis of one-dimensional (1-D) hierarchical NiO nanosheets covering bamboo-like amorphous CNT composites (NiO@CNT) via a facile and a low-cost solution route based on sulfonated polymeric nanotubes (PNTs) used simultaneously as both, a template, and a source of nano-structured carbon derived by a low-temperature thermal carbonization treatment. The electrochemical performance of the NiO@CNT composite electrode indicate that this novel hybrid nanostructure is potentially capable of delivering excellent reversible capacity when used as an anode material in a lithium-ion battery (LIB). A large discharge capacity of 1034 mAh g⁻¹ is delivered by the NiO@CNT composite even after 300 cycles at a relatively high current density of 800 mA g⁻¹, with an average coulombic efficiency of 98.1%. A significant achievement in the reversible capacity of the NiO@CNT composite is attributed to the outstanding nanostructure resulting in synergistic effects of the hollow amorphous CNT backbone and ultrathin NiO nanosheets. Furthermore, the generic solution method to fabricate 1-D metal oxides@amorphous CNT nanostructures, developed in this work, is expected to have a wide range of applications in improving the properties of transition metal oxides.     

Dopamine derived nitrogen-doped carbon sheets as anode materials for high-performance sodium ion batteries

Designed as an anode material for sodium ion batteries, nitrogen-doped carbon sheets (NCSs) were successfully synthesized using graphene and dopamine as template and carbon precursor, respectively. The NCSs demonstrate high reversible capacity and excellent rate performance, delivering a high reversible capacity of 382 mAh g⁻¹ at 50 mA g⁻¹ after 55 cycles. Even up to 10 A g⁻¹, a rate capacity of 75 mAh g⁻¹ can be obtained. Furthermore, NCSs also have remarkable cycling stability with specific capacity of 165 mAh g⁻¹ after 600 cycles (under 200 mA g⁻¹). The excellent performance of NCSs can be ascribed to the nitrogen-doped two-dimension sheet structure.     

Ag enhanced electrochemical performance for Na2Li2Ti6O14 anode in rechargeable lithium-ion batteries

Due to the characteristics of an electronic insulator, Na₂Li₂Ti₆O₁₄ always suffers from low electronic conductivity as anode material for lithium storage. Via Ag coating, Na₂Li₂Ti₆O₁₄@Ag is fabricated, which has higher electronic conductivity than bare Na₂Li₂Ti₆O₁₄. Enhancing the Ag coating content from 0.0 to 10.0 wt%, the surface of Na₂Li₂Ti₆O₁₄ is gradually deposited by Ag nanoparticles. At 6.0 wt%, a continuous Ag conductive layer is formed on Na₂Li₂Ti₆O₁₄. While, particle growth and aggregation take place when the Ag coating content reaches 10.0 wt%. As a result, Na₂Li₂Ti₆O₁₄@6.0 wt% Ag displays better cycle and rate properties than other samples. It can deliver a lithium storage capacity of 131.4 mAh g⁻¹ at 100 mA g⁻¹, 124.9 mAh g⁻¹ at 150 mA g⁻¹, 119.1 mAh g⁻¹ at 200 mA g⁻¹, 115.8 mAh g⁻¹ at 250 mA g⁻¹, 111.9 mAh g⁻¹ at 300 mA g⁻¹ and 109.4 mAh g⁻¹ at 350 mA g⁻¹, respectively.     

Carbon-coated SiO/ZrO2 composites as anode materials for lithium-ion batteries

A combination of high-energy ball milling and constant pressure chemical vapor deposition was used to prepare carbon-coated SiO/ZrO₂ composites. It was found that the as-prepared composites were composed of amorphous carbon, amorphous SiO, and paracryslalline ZrO₂. The electrochemical analysis results revealed excellent electrochemical performances for the composites, including a high initial discharge capacity (1737 mA h g⁻¹), a remarkable cyclic stability (reversible capacity of 721 mA h g⁻¹ at 800 mA g⁻¹, after 100 cycles), and a good rate capability (870 mA h g⁻¹ at 800 mA g⁻¹). These features demonstrate that these composites are promising alternative candidates for high-efficiency electrode materials of Li-ion batteries.     

Three-dimensional wire-in-tube hybrids of tin dioxide and nitrogen-doped carbon for lithium ion battery applications

Design and fabrication of tin dioxide/carbon composites with peculiar nanostructures have been proven to be an effective strategy for improving the electrochemical performance of tin dioxide-based anode for lithium-ion batteries, and thus have attracted extensive attention. Herein, we have successfully prepared a uniquely three-dimensional and interweaved wire-in-tube nanostructure of nitrogen-doped carbon nanowires encapsulated into tin dioxide@carbon nanotubes, denoted as NCNW@void@SnO₂@C, via a facile and novel approach for the first time. Interestingly, one-dimension void space located between nitrogen-doped carbon nanowires and innermost wall of tin dioxide@carbon tubes is also formed. The possible formation mechanism of wire-in-tube nanostructure is also discussed and determined by transmission electron microscopy, X-ray diffraction measurement, laser Raman spectroscopy and X-ray photoelectron spectroscopy characterizations. This unique NCNW@void@SnO₂@C fully combines all the advantages of using a three-dimensional architecture, hollow structure, carbon coating, and a mechanically robust carbon nanowires support, thus exhibiting an excellent electrochemical performance as promising anode materials for lithium-ion batteries. A high reversible capacity of 721.3 mAh g⁻¹ can be remained even after 500 cycles at a current density of 200 mA g⁻¹, as well as a capacity of 456.7 mAh g⁻¹ is obtained even at 3000 mA g⁻¹.     

Nitrogen-doped carbon nanofibers derived from polyacrylonitrile for use as anode material in sodium-ion batteries

Nitrogen-doped carbon nanofibers (N-CNFs) derived from polyacrylonitrile were successfully synthesized by a combination of electrospinning and thermal treatment processes. The as-prepared N-CNFs were used as anode material for sodium-ion batteries due to their unique fabric and weakly-ordered turbostratic structure as well as large spacing between graphene layers. Results show that N-CNFs carbonized at 800 °C delivered a high reversible capacity of 293 mAh g⁻¹ at a current density of 50 mA g⁻¹ in the first cycle. Even though the first-cycle Coulombic efficiency was 64%, it increased to nearly 100% only after a few initial cycles. Additionally, these N-CNFs showed excellent cycling and high-rate performance, and maintained a capacity of up to 150 mAh g⁻¹ even at an extremely high current density of 1000 mA g⁻¹ for over 200 cycles. It is, therefore, demonstrated that N-CNFs prepared under appropriate conditions are promising anode material candidate for sodium-ion batteries.     

Iodine doped graphene as anode material for lithium ion battery

I-doped graphene is synthesized by a facile heat treatment method and used as anode material for lithium ion battery. The doped graphene exhibits high reversible capacity (1690 mAh g⁻¹ at 100 mA g⁻¹), good cyclability (retaining 92.6% reversible capacity after 200 cycles) and excellent rate performance compared with undoped graphene. The superior electrochemical performance of the I-doped graphene is explained by the change of graphene lattice, defects and positive charge density introduced by the doping of I atoms.     

Evaluation of reduced graphene oxide-supported NiSb2O6 nanocomposites for reversible lithium storage

NiSb₂O₆ and reduced graphene oxide (NiSb₂O₆/rGO) nanocomposites are successfully fabricated by a solid-state method combined with a subsequent solvothermal treatment and further used as anode material of lithium-ion battery. The NiSb₂O₆/rGO nanocomposites exhibit a higher reversible capacity (of ca. 1240.5 mA h g⁻¹ at a current density of 50 mA g⁻¹), along with a good rate capability (395.2 mA h g⁻¹ at a current density of 1200 mA g⁻¹) and excellent capacity retention (684.5 mA h g⁻¹ after 150 cycles). These good performances could be attributed to the incorporated reduced grapheme oxide, which significantly improves the electronic conductivity of the NiSb₂O₆.     

Facile synthesis of porous hollow Co3O4 microfibers derived-from metal-organic frameworks as an advanced anode for lithium ion batteries

Co₃O₄, as a promising anode material for the next generation lithium ion batteries to replace graphite, displays high theoretical capacity (890 mAh g⁻¹) and excellent electrochemical properties. However, the drawbacks of its poor cycle performance caused by large volume changes during charge-discharge process and low initial coulombic efficiency due to large irreversible reaction impede its practical application. Herein, we have developed a porous hollow Co₃O₄ microfiber with 500 nm diameter and 60 nm wall thickness synthesized via a facile chemical precipitation method with subsequent thermal decomposition. As an advanced anode for lithium ion batteries, the porous hollow Co₃O₄ microfibers deliver an obviously enhanced electrochemical property in terms of lithium storage capacity (1177.4 mA h g⁻¹ at 100 mA g⁻¹), initial coulombic efficiency (82.9%) and cycle performance (76.6% capacity retention at 200th cycle). This enhancement could be attributed to the well-designed microstructure of porous hollow Co₃O₄ microfibers, which could increase the contact surface area between electrolyte and active materials and accommodate the volume variations via additional void space during cycling.     

Promising graphene/carbon nanotube foam@π-conjugated polymer self-supporting composite cathodes for high-performance rechargeable lithium batteries

Three-dimensional (3D) graphene foam materials are highly favored due to large accessible surface and excellent conductive network, which can be commendably applied as self-supporting electrodes for advanced rechargeable lithium batteries (RLBs). Here, promising graphene nanosheets/acid-treated multi-walled carbon nanotubes (GNS/aMWCNT)-supported 1,5-diaminoanthraquinone (DAA) organic foams [oGCTF(DAA)] are prepared by organic solvent displacement method followed by solvothermal reaction. And then electrochemical polymerization is carried out to obtain 3D porous GNS/aMWCNT organic foam-supported poly(1,5-diaminoanthraquinone) (oGCTF@PDAA) nanocomposites, which achieves the ordered growth of homogeneous PDAA nanoparticles on GNS/aMWCNT surface due to the role of oGCTF(DAA). Such structure largely improves PDAA utilization, facilitates charge transportation and suppresses the dissolution of PDAA. As a result, the oGCTF@PDAA cathode for RLBs delivers a high discharge capacity of 289 mAh g⁻¹ at 30 mA g⁻¹ and still retains 122 mAh g⁻¹ at extreme 10 A g⁻¹ for rapid charging/discharging. Moreover, superior cycling stability is achieved with only 14.8% capacity loss after 2000 cycles even at a high current density of 1 A g⁻¹.     

Functionalized N-doped interconnected carbon nanofibers as an anode material for sodium-ion storage with excellent performance

The electrochemical performance of sodium-ion battery was improved by using functionalized interconnected N-doped carbon nanofibers (FN-CNFs) as the anode. The material was synthesized with polypyrrole as precursor by a simple method. The FN-CNF electrode exhibits excellent rate capability and cycling stability, delivering a capacity of 134.2 mAh g⁻¹ at a high current density of 200 mA g⁻¹ after 200 cycles and retains a capacity of 73 mAh g⁻¹ even at an extremely high current density of 20 A g⁻¹. The superior performance can be attributed to N-doped sites and functionalized groups, which are capable of capturing sodium ions rapidly and reversibly through surface adsorption and surface redox reactions.     

Three-dimensional hierarchical ZnCo2O4 flower-like microspheres assembled from porous nanosheets: Hydrothermal synthesis and electrochemical properties

In this work, three-dimensional hierarchical ZnCo₂O₄ flower-like microspheres have been synthesized on a large scale via a facile and economical citrate-mediated hydrothermal method followed by an annealing process in air. The as-synthesized ZnCo₂O₄ flower-like microspheres are constructed by numerous interweaving porous nanosheets. According to the experimental results, a formation mechanism involving the assembly of the nanosheets from nanoparticles into flower-like microsphere is proposed. As a virtue of their beneficial structural features, the ZnCo₂O₄ flower-like microspheres exhibit a high lithium storage capacity and excellent cycling stability (1136 mA h g⁻¹ at 100 mA g⁻¹ after 50 cycles). This remarkable electrochemical performance can be ascribed to the hierarchical structure and porous structures in the nanosheets, which effectively increases the contact area between the active materials and the electrolyte, shortening the Li⁺ diffusion pathway and buffering the volume variation during cycling.     

One-step synthesis of Li-doped NiO as high-performance anode material for lithium ion batteries

The poor electronic conductivity and huge volume expansion of NiO are the vital barriers when used as anode for lithium ion batteries. In order to solve above issues, Li-doped NiO are prepared by a facile one-step ultrasonic spray pyrolysis method. The effects of Li doping on the morphology, structure and chemical composition of the Li-doped NiO powders are extensively studied. When used as lithium ion batteries anode, it is demonstrated that the doping of Li has significant positive effect on improving the electrochemical performance. After 100 cycles at 400 mA g⁻¹, The Li-doped NiO samples deliver a discharge capacity of 907 mAh g⁻¹, much more than that of un-doped sample (736 mAh g⁻¹). The improved electrochemical performances can be ascribed to the improved p-type conductivity and lower impedance, which are confirmed by Rietveld refinement, X-ray photoelectron spectroscopy and electron impedance spectroscopy.     

Carbon coated porous tin peroxide/carbon composite electrode for lithium-ion batteries with excellent electrochemical properties

A porous tin peroxide/carbon (SnO₂/C) composite electrode coated with an amorphous carbon layer is prepared using a facile method. In this electrode, spherical graphite particles act as supporter of electrode framework, and the interspace among particles is filled with porous amorphous carbon derived from decomposition of polyvinylidene fluoride and polyacrylonitrile. SnO₂ nanoparticles are uniformly embedded in the porous amorphous carbon matrix. The pores in amorphous carbon matrix are able to buffer the huge volume expansion of SnO₂ during charge/discharge cycling, and the carbon framework can prevent the SnO₂ particles from pulverization and re-aggregation. The carbon coating layer on the outermost surface of electrode can further prevent porous SnO₂/C electrode from contacting with electrolyte directly. As a result, the repeated formation of solid electrolyte interface is avoided and the cycling stability of electrode is improved. The obtained SnO₂/C electrode presents an initial coulombic efficiency of 77.3% and a reversible capacity of 742 mA h g⁻¹ after 130 cycles at a current density of 100 mA g⁻¹. Furthermore, a reversible capacity of 679 mA h g⁻¹ is obtained at 1 A g⁻¹.     

Nitrogen-doping of chemically reduced mesocarbon microbead oxide for the improved performance of lithium ion batteries

Nitrogen was doped into chemically-reduced mesocarbon microbead oxide (CR-MCMBO) through simple annealing in ammonia at 800 °C, and the Li-ion storage properties of the prepared nitrogen-doped CR-MCMBO (NR-MCMBO) was studied. It was found that NR-MCMBO shows a highly reversible capacity of 762 mAh g^?1 at 20 mA g^?1 during the first charge process, which is much higher than that of the pristine MCMB (289 mAh g^?1), and the specific capacity of NR-MCMBO still had a value of 535 mAh g^?1 after 200 cycles. When the current density reaches 1000 mA g^?1, the specific capacity of NR-MCMBO is 388 mAh g^?1. The high reversible capacity of NR-MCMBO is attributed to the high amount of pyridinic nitrogen and the large number of defects induced by oxidation and nitrogen-doping. Moreover, the open pores constituted by graphene-like nanoplatelets on the spherical NR-MCMBO surface facilitate the diffusion of Li ions.     

Synthesis and characterization of porous maghemite as an anode for Li-ion batteries

The synthesis of porous maghemite via a simple glycerol-mediated solution method was successfully accomplished. Thermal analysis, X-ray diffraction and Mössbauer spectroscopy results disclosed the formation of maghemite. The morphological and structural features of maghemite were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, and nitrogen adsorption–desorption. The powder showed Brunauer–Emmett–Teller surface area of 285 m² g⁻¹ with micro-, meso- and macropores.The anode body was doctor bladed using primary powder with a binder and a conductive agent. Galvanostatic charge–discharge cycling of the porous maghemite exhibited a specific reversible capacity of approximately 1180 mAh g⁻¹ at 100 mA g⁻¹ current density, which was two times higher than that of common nanomaghemite with average particle size of 19 nm. The cell showed stability even at the high current charge–discharge rates of 3000 mA g⁻¹ and more than 94% retention. After multiple high current cycling regimes, the cell recovered to nearly full reversible capacity of ~1120 mAh g⁻¹ at 100 mA g⁻¹. The reason for this remarkable performance of the present anode was thought to be dependent upon the role of pores in increasing the surface area and resistance against volume changes during lithium insertion/extraction.     

Porous carbon spheres as anode materials for sodium-ion batteries with high capacity and long cycling life

Porous carbon spheres (PCSs) with high surface area were fabricated by the reaction of D-Glucose monohydrate precursor with sodium molybdate dihydrate (Na₂MoO₄·2H₂O) via a facile hydrothermal method followed by carbonization and aqueous ammonia solution (NH₃·H₂O) treatment. The as-prepared PCSs exhibit a highly developed porous structure with a large specific surface area and show an excellent electrochemical performance as anode material of sodium-ion batteries (SIBs). A reversible capacity of 249.9 mA h g⁻¹ after 50 cycles at a current density of 50 mA g⁻¹ and a long cycling life at a high current density of 500 mA g⁻¹ are achieved. The excellent cycling performance and high capacity make the PCSs a promising candidate for long cycling SIBs.