Preparation and lithium storage of core–shell honeycomb-like Co3O4@C microspheres

Core–shell honeycomb-like Co₃O₄@C microspheres were synthesized via a facile solvothermal method and subsequent annealing treatment under an argon atmosphere. Owing to the core–shell honeycomb-like structure, a long cycling life was achieved (a high reversible specific capacity of 318.9 mA h g⁻¹ was maintained at 5C after 1000 cycles). Benefiting from the coated carbon layers, excellent rate capability was realized (a reversible specific capacity as high as 332.6 mA h g⁻¹ was still retained at 10C). The design of core–shell honeycomb-like microspheres provides a new idea for the development of anode materials for high-performance lithium-ion batteries.

The reversible specific capacity of CSHCo₃O₄@C microspheres was as high as 332.6 mA h g⁻¹ at 10C, which was significantly higher than that of SCo₃O₄ microspheres (68.7 mA h g⁻¹).     

Preparation of 3D hierarchical porous Co3O4 nanostructures with enhanced performance in lithium-ion batteries

Three-dimensional hierarchical Co₃O₄ microspheres assembled by well-aligned 1D porous nanorods have been synthesized by hydrothermal methods with the help of CTAB and subsequent heat treatment. The morphology and compositional characteristics of the hierarchical Co₃O₄ microspheres have been investigated using different techniques. Based on the SEM and TEM analyses, the growth direction of the nanorods is in the [110] direction. The hierarchical Co₃O₄ microspheres have a comparatively large Brunauer–Emmett–Teller surface area of about 50.2 m²g⁻¹, and pore size distribution is mainly concentrated at 12 nm. On the basis of the time tracking experiment, a possible growth mechanism has been proposed. It demonstrates that the overall mechanism includes nucleation, oriented growth and self-assembly processes. These hierarchical Co₃O₄ microspheres provide several favorable features for Li-ion battery applications: (1) large Brunauer–Emmett–Teller surface area, (2) porous structure, and (3) hierarchical structure. Therefore, measurement of the electrochemical properties indicates that the specific capacity can maintain a stable value of about 1942 mA h g⁻¹ at a current of 100 mA g⁻¹ within 100 cycles.

Three-dimensional hierarchical Co₃O₄ microspheres assembled by well-aligned 1D porous nanorods were successfully fabricated. The sample exhibited excellent electrochemical properties as anode materials for LIBs.     

Rationally designed hierarchical porous CNFs/Co3O4 nanofiber-based anode for realizing high lithium ion storage

To achieve a high power density of lithium-ion batteries, it is essential to develop anode materials with high capacity and excellent stability. Cobalt oxide (Co₃O₄) is a prospective anode material on account of its high energy density. However, the poor electrical conductivity and volumetric changes of the active material induce a dramatic decrease in capacity during cycling. Herein, a hierarchical porous hybrid nanofiber of ZIF-derived Co₃O₄ and continuous carbon nanofibers (CNFs) is rationally constructed and utilized as an anode material for lithium-ion batteries. The PAN/ZIF-67 heterostructure composite nanofibers were first synthesized using electrospinning technology followed by the in situ growth method, and then the CNFs/Co₃O₄ nanofibers were obtained by subsequent multi-step thermal treatment. The continuous porous conductive carbon backbone not only effectively provides a channel to expedite lithium ion diffusion and electrode transfer, but also accommodates volume change of Co₃O₄ during the charge–discharge cycling process. The electrode exhibits a high discharge capacity of 1352 mA h g⁻¹ after 500 cycles at a constant current density of 0.2 A g⁻¹. Additionally, the composites deliver a discharge capacity of 661 mA h g⁻¹ with a small capacity decay of 0.078% per cycle at a high current density of 2 A g⁻¹ after 500 cycles. This hierarchical porous structural design presents an effective strategy to develop a hybrid nanofiber for improving lithium ion storage.

Hierarchical porous CNFs/Co₃O₄ nanofiber is rationally designed and constructed as an anode for achieving high capacity and stable lithium ion batteries.     

Hierarchical porous ZnMnO3 yolk–shell microspheres with superior lithium storage properties enabled by a unique one-step conversion mechanism

ZnMnO₃ has attracted enormous attention as a novel anode material for rechargeable lithium-ion batteries due to its high theoretical capacity. However, it suffers from capacity fading because of the large volumetric change during cycling. Here, porous ZnMnO₃ yolk–shell microspheres are developed through a facile and scalable synthesis approach. This ZnMnO₃ can effectively accommodate the large volume change upon cycling, leading to an excellent cycling stability. When applying this ZnMnO₃ as the anode in lithium-ion batteries, it shows a remarkable reversible capacity (400 mA h g⁻¹ at a current density of 400 mA g⁻¹ and 200 mA h g⁻¹ at 6400 mA g⁻¹) and excellent cycling performance (540 mA h g⁻¹ after 300 cycles at 400 mA g⁻¹) due to its unique structure. Furthermore, a novel conversion reaction mechanism of the ZnMnO₃ is revealed: ZnMnO₃ is first converted into intermediate phases of ZnO and MnO, after which MnO is further reduced to metallic Mn while ZnO remains stable, avoiding the serious pulverization of the electrode brought about by lithiation of ZnO.

ZnMnO₃ has attracted enormous attention as a novel anode material for rechargeable lithium-ion batteries due to its high theoretical capacity.     

Facile thermochemical conversion of FeOOH nanorods to ZnFe2O4 nanorods for high-rate lithium storage

We successfully prepared ZnFe₂O₄ nanorods (ZFO-NRs) by a simple thermochemical reaction of FeOOH nanorods with Zn(NO₃)₂ to use as an anode material in lithium-ion batteries. The FeOOH nanorod shape was well maintained after conversion into ZFO-NR with the formation of porous structures. The nanorod structure and porous morphology facilitate Li⁺ transport, improve the reaction rates owing to the larger contact area with the electrolyte, and reduce the mechanical stress during lithiation/delithiation. The ZFO-NR electrode exhibited a reversible capacity of 725 mA h g⁻¹ at 1 A g⁻¹ and maintained a capacity of 668 mA h g⁻¹ at 2 A g⁻¹; these capacities are much higher and more stable than those of ZFO nanoparticles prepared by a hydrothermal method (ZFO-HT) (216 and 117 mA h g⁻¹ at 1 and 2 A g⁻¹, respectively). Although ZFO-NRs exhibited high, stable capacities at moderate current densities for charging and discharging, the capacity rapidly decreased under fast charging/discharging conditions (>4 A g⁻¹). However, carbonized ZFO-NR (C/ZFO-NR) exhibited an improved reversible capacity and rate capability resulting from an increased conductivity compared with ZFO-NRs. The specific capacity of C/ZFO-NRs at 1 A g⁻¹ was 765 mA h g⁻¹; notably, a capacity of 680 mA h g⁻¹ was maintained at 6 A g⁻¹.

ZnFe₂O₄ nanorods were prepared by a simple thermochemical conversion of FeOOH nanorods, and exhibited an improved reversible capacity and rate capability.     

Preparation of Sn-aminoclay (SnAC)-templated Fe3O4 nanoparticles as an anode material for lithium-ion batteries

Sn-aminoclay (SnAC)-templated Fe₃O₄ nanocomposites (SnAC–Fe₃O₄) were prepared through a facile approach. The morphology and macro-architecture of the fabricated SnAC–Fe₃O₄ nanocomposites were characterized by different techniques. A constructed meso/macro-porous structure arising from the homogeneous dispersion of Fe₃O₄ NPs on the SnAC surface owing to inherent NH₃⁺ functional groups provides new conductive channels for high-efficiency electron transport and ion diffusion. After annealing under argon (Ar) gas, most of SnAC layered structure can be converted to SnO₂; this carbonization allows for formation of a protective shell preventing direct interaction of the inner SnO₂ and Fe₃O₄ NPs with the electrolyte. Additionally, the post-annealing formation of Fe–O–C and Sn–O–C bonds enhances the connection of Fe₃O₄ NPs and SnAC, resulting in improved electrical conductivity, specific capacities, capacity retention, and long-term stability of the nanocomposites. Resultantly, electrochemical measurement exhibits high initial discharge/charge capacities of 980 mA h g⁻¹ and 830 mA h g⁻¹ at 100 mA g⁻¹ in the first cycle and maintains 710 mA h g⁻¹ after 100 cycles, which corresponds to a capacity retention of ∼89%. The cycling performance at 100 mA g⁻¹ is remarkably improved when compared with control SnAC. These outstanding results represent a new direction for development of anode materials without any binder or additive.

Sn-aminoclay (SnAC)/Fe₃O₄ NPs – a promising hybrid electrode to offer great electrochemical performance with a high initial discharge of 980 mA h g⁻¹ and good capacity retention of 89% after 100 cycles.     

Sb2O3 nanoparticles anchored on N-doped graphene nanoribbons as improved anode for sodium-ion batteries

Sodium-ion batteries (SIBs) are emerging as a promising alternative to conventional lithium-ion technology, due to the abundance of sodium resources. Still, major drawbacks for the commercial application of SIBs lie in the slow kinetic processes and poor cycling performance of the devices. In this work, a hybrid nanocomposite of Sb₂O₃ nanoparticles anchored on N-doped graphene nanoribbons (GNR) is implemented as anode material in SIBs. The obtained Sb₂O₃/N-GNR anode delivers a reversible specific capacity of 642 mA h g⁻¹ after 100 cycles at 0.1 A g⁻¹ and exhibits a good rate capability. Even after 500 cycles at 5 A g⁻¹, the specific capacity is maintained at about 405 mA h g⁻¹. Such good Na storage performance is mainly ascribed to the beneficial effect of N doping for charge transfer and to the improved microstructure that facilitates the Na⁺ diffusion through the overall electrode.

A hybrid nanocomposite of Sb₂O₃ nanoparticles anchored on N-doped graphene nanoribbons is used as anode in SIBs. These hybrid electrodes demonstrate a high charge transfer and improved microstructure, facilitating the Na⁺ diffusion in the electrode.     

Self-assembled hierarchical porous NiMn2O4 microspheres as high performance Li-ion battery anodes

Hierarchical structured porous NiMn₂O₄ microspheres assembled with nanorods are synthesized through a simple hydrothermal method followed by calcination in air. As anode materials for lithium ion batteries (LIBs), the NiMn₂O₄ microspheres exhibit a high specific capacity. The initial discharge capacity is 1126 mA h g⁻¹. After 1000 cycles, the NiMn₂O₄ demonstrates a reversible capacity of 900 mA h g⁻¹ at a current density of 500 mA g⁻¹. In particular, the porous NiMn₂O₄ microspheres still could deliver a remarkable discharge capacity of 490 mA h g⁻¹ even at a high current density of 2 A g⁻¹, indicating their potential application in Li-ion batteries. This excellent electrochemical performance is ascribed to the unique hierarchical porous structure which can provide sufficient contact for the transfer of Li⁺ ion and area for the volume change of the electrolyte leading to enhanced Li⁺ mobility.

Hierarchical structured porous NiMn₂O₄ microspheres assembled with nanorods are synthesized through a simple hydrothermal method followed by calcination in air.     

Preparation of novel two-stage structure MnO micrometer particles as lithium-ion battery anode materials

MnO micrometer particles with a two-stage structure (composed of mass nanoparticles) were produced via a one-step hydrothermal method using histidine and potassium permanganate (KMnO₄) as reagents, with subsequent calcination in a nitrogen (N₂) atmosphere. When the MnO micrometer particles were utilized in lithium-ion batteries (LIBs) as anode materials, the electrode showed a high reversible specific capacity of 747 mA h g⁻¹ at 100 mA g⁻¹ after 100 cycles, meanwhile, the electrode presented excellent rate capability at various current densities from 100 to 2000 mA g⁻¹ (∼203 mA h g⁻¹ at 2000 mA g⁻¹). This study developed a new approach to prepare two-stage structure micrometer MnO particles and the sample can be a promising anode material for lithium-ion batteries.

MnO micrometer particles with a two-stage structure (composed of mass nanoparticles) were produced via a one-step hydrothermal method using histidine and potassium permanganate (KMnO₄) as reagents, with subsequent calcination in a nitrogen (N₂) atmosphere.     

Synthesis and electrochemical performance of NaV3O8 nanobelts for Li/Na-ion batteries and aqueous zinc-ion batteries

NaV₃O₈ nanobelts were successfully synthesized for Li/Na-ion batteries and rechargeable aqueous zinc-ion batteries (ZIBs) by a facile hydrothermal reaction and subsequent thermal transformation. Compared to the electrochemical performance of LIBs and NIBs, NaV₃O₈ nanobelt cathode materials in ZIBs have shown excellent electrochemical performance, including high specific capacity of 421 mA h g⁻¹ at 100 mA g⁻¹ and good cycle stability with a capacity retention of 94% over 500 cycles at 5 A g⁻¹. The good diffusion coefficients and high surface capacity of NaV₃O₈ nanobelts in ZIBs were in favor of fast Zn²⁺ intercalation and long-term cycle stability.

Compared to the electrochemical performance for LIBs and NIBs, NaV₃O₈ nanobelts electrode for ZIBs shows excellent electrochemical performance, including high specific capacity of 421 mA h g⁻¹ at 100 mA g⁻¹, good rate performance and cycle performance.     

Controllable synthesis of nanostructured ZnCo2O4 as high-performance anode materials for lithium-ion batteries

Nanostructured ZnCo₂O₄ anode materials for lithium-ion batteries (LIBs) have been successfully prepared by a two-step process, combining facile and concise electrospinning and simple post-treatment techniques. Three different structured ZnCo₂O₄ anodes (nanoparticles, nanotubes and nanowires) can be prepared by simply adjusting the ratio of metallic salt and PVP in the precursor solutions. Charge–discharge tests and cyclic voltammetry (CV) have been conducted to evaluate the lithium storage performances of ZnCo₂O₄ anodes, particularly for ZnCo₂O₄ nanotubes obtained from a weight ratio 2 : 4 of metallic salt and PVP polymer in the precursor solution. Remarkably, ZnCo₂O₄ nanotubes exhibit high specific capacity, good rate property, and long cycling stability. Reversible capacity is still maintained at 1180.8 mA h g⁻¹ after 275 cycles at a current density of 200 mA g⁻¹. In case of rate capability, even after cycling at the 2000 mA g⁻¹ current density, the capacity could recover to 684 mA h g⁻¹. The brilliant electrochemical properties of the ZnCo₂O₄ anodes make them promising anodes for LIBs and other energy storage applications.

ZnCo₂O₄ nanoparticles, nanotubes, and nanofibers can be controllably prepared by simply tuning the weight ratios of metallic salts and PVP polymer in the precursor solution.     

An investigation of Li2TiO3–coke composite anode material for Li-ion batteries

Anode material Li₂TiO₃–coke was prepared and tested for lithium-ion batteries. The as-prepared material exhibits excellent cycling stability and outstanding rate performance. Charge/discharge capacities of 266 mA h g⁻¹ at 0.100 A g⁻¹ and 200 mA h g⁻¹ at 1.000 A g⁻¹ are reached for Li₂TiO₃–coke. A cycling life-time test shows that Li₂TiO₃–coke gives a specific capacity of 264 mA h g⁻¹ at 0.300 A g⁻¹ and a capacity retention of 92% after 1000 cycles of charge/discharge.

Anode material Li₂TiO₃–coke was prepared and tested for lithium-ion batteries. The as-prepared material exhibits excellent cycling stability and outstanding rate performance.     

Preparation of cobalt sulfide@reduced graphene oxide nanocomposites with outstanding electrochemical behavior for lithium-ion batteries

Cobalt sulfide@reduced graphene oxide composites were prepared through a simple solvothermal method. The cobalt sulfide@reduced graphene oxide composites are composed of cobalt sulfide nanoparticles uniformly attached on both sides of reduced graphene oxide. Some favorable electrochemical performances in specific capacity, cycling performance, and rate capability are achieved using the porous nanocomposites as an anode for lithium-ion batteries. In a half-cell, it exhibits a high specific capacity of 1253.9 mA h g⁻¹ at 500 mA g⁻¹ after 100 cycles. A full cell consists of the cobalt sulfide@reduced graphene oxide nanocomposite anode and a commercial LiCoO₂ cathode, and is able to hold a high capacity of 574.7 mA h g⁻¹ at 200 mA g⁻¹ after 200 cycles. The reduced graphene oxide plays a key role in enhancing the electrical conductivity of the electrode materials; and it effectively prevents the cobalt sulfide nanoparticles from dropping off the electrode and buffers the volume variation during the discharge–charge process. The cobalt sulfide@reduced graphene oxide nanocomposites present great potential to be a promising anode material for lithium-ion batteries.

Cobalt sulfide@reduced graphene oxide nanocomposites obtained through a dipping and hydrothermal process, exhibit ascendant lithium-ion storage properties.     

Electrochemical studies of a high voltage Na4Co3(PO4)2P2O7–MWCNT composite through a selected stable electrolyte

Cathode materials that operate at high voltages are required to realize the commercialization of high-energy-density sodium-ion batteries. In this study, we prepared different composites of sodium cobalt mixed-phosphate with multiwalled carbon nanotubes (Na₄Co₃(PO₄)₂P₂O₇–MWCNTs) by the sol–gel synthesis technique. The crystal structure and microstructure were characterized by using PXRD, TGA, Raman spectroscopy, SEM and TEM. The electrochemical properties of the Na₄Co₃(PO₄)₂P₂O₇–20 wt% MWCNT composite were explored using two different electrolytes. The composite electrode exhibited excellent cyclability and rate capabilities with the electrolyte composed of 1 M sodium hexafluorophosphate in ethylene carbonate:dimethyl carbonate (EC:DMC). The composite electrode delivered stable discharge capacities of 80 mA h g⁻¹ and 78 mA h g⁻¹ at room and elevated (55 °C) temperatures, respectively. The average discharge voltage was around 4.45 V versus Na⁺/Na, which corresponded to the Co^2+/3+ redox couple. The feasibility of the Na₄Co₃(PO₄)₂P₂O₇ cathode for sodium-ion batteries has been confirmed in real time using a full cell configuration vs. NaTi₂(PO₄)₃–20 wt% MWCNT, and it delivers an initial discharge capacity of 78 mA h g⁻¹ at 0.2C rate.

Na₄Co₃(PO₄)₂P₂O₇–MWCNT composites in 1 M NaPF₆ in EC:DMC electrolytes deliver stable discharge capacities of 80 mA h g⁻¹ and 78 mA h g⁻¹ at normal and elevated temperatures, respectively. In a full cell configuration vs. NaTi₂(PO₄)₃–MWCNT, they deliver an initial discharge capacity of 78 mA h g⁻¹ at 0.2C rate.     

Role of polyvinylpyrrolidone in the electrochemical performance of Li2MnO3 cathode for lithium-ion batteries

While Li₂MnO₃ as an over-lithiated layered oxide (OLO) shows a significantly high reversible capacity of 250 mA h g⁻¹ in lithium-ion batteries (LIBs), it has critical issues of poor cycling performance and deteriorated high rate performance. In this study, modified OLO cathode materials for improved LIB performance were obtained by heating the as-prepared OLO at different temperatures (400, 500, and 600 °C) in the presence of polyvinylpyrrolidone (PVP) under an N₂ atmosphere. Compared to the as-prepared OLO, the OLO sample heated at 500 °C with PVP exhibited a high initial discharge capacity of 206 mA h g⁻¹ and high rate capability of 111 mA h g⁻¹ at 100 mA g⁻¹. The superior performance of the OLO sample heated at 500 °C with PVP is attributed to an improved electronic conductivity and Li⁺ ionic motion, resulting from the formation of the graphitic carbon structure and increased Mn³⁺ ratio during the decomposition of PVP.

The modified OLO cathode materials for improved LIB performance were obtained by heating the as-prepared OLO in the presence of polyvinylpyrrolidone (PVP) under an N₂ atmosphere.     

Design of highly porous Fe3O4@reduced graphene oxide via a facile PMAA-induced assembly

Advances in the synthesis and processing of graphene-based materials have presented the opportunity to design novel lithium-ion battery (LIB) anode materials that can meet the power requirements of next-generation power devices. In this work, a poly(methacrylic acid) (PMAA)-induced self-assembly process was used to design super-mesoporous Fe₃O₄ and reduced-graphene-oxide (Fe₃O₄@RGO) anode materials. We demonstrate the relationship between the media pH and Fe₃O₄@RGO nanostructure, in terms of dispersion state of PMAA-stabilized Fe₃O₄@GO sheets at different surrounding pH values, and porosity of the resulted Fe₃O₄@RGO anode. The anode shows a high surface area of 338.8 m² g⁻¹ with a large amount of 10–40 nm mesopores, which facilitates the kinetics of Li-ions and electrons, and improves electrode durability. As a result, Fe₃O₄@RGO delivers high specific-charge capacities of 740 mA h g⁻¹ to 200 mA h g⁻¹ at various current densities of 0.5 A g⁻¹ to 10 A g⁻¹, and an excellent capacity-retention capability even after long-term charge–discharge cycles. The PMAA-induced assembly method addresses the issue of poor dispersion of Fe₃O₄-coated graphene materials—which is a major impediment in the synthesis process—and provides a facile synthetic pathway for depositing Fe₃O₄ and other metal oxide nanoparticles on highly porous RGO.

Advances in the synthesis and processing of graphene-based materials have presented the opportunity to design novel lithium-ion battery (LIB) anode materials that can meet the power requirements of next-generation power devices.     

Three-dimensional hierarchical ZnCo2O4@C3N4-B nanoflowers as high-performance anode materials for lithium-ion batteries

ZnCo₂O₄ has become one of the most widely used anode materials due to its good specific capacity, cost-efficiency, high thermal stability and environmental benignity. However, its poor conductivity and cycle stability have limited its practical application in lithium-ion batteries. To overcome these issues, we constructed a 3D nanoflower composite material (ZnCo₂O₄@C₃N₄-B) by combining ZnCo₂O₄ as a framework and B-doped g-C₃N₄ (g-C₃N₄-B) as a new carbon source material via a simple hydrothermal method. ZnCo₂O₄@C₃N₄-B exhibited exceptional specific capacitance of 919.76 mA h g⁻¹ after 500 cycles at 0.2 A g⁻¹ and a long-term capacity retention of 97.8% after 1000 cycles at 2 A g⁻¹. The high reversible capacity, long cycling life and good rate performance could be attributed to the 3D interconnected architecture and doping of g-C₃N₄-B. This work provides a simple and general strategy to design high-performance anode materials for lithium-ion batteries to meet the needs of practical applications.

ZnCo₂O₄ has become one of the most widely used anode materials due to its good specific capacity, cost-efficiency, high thermal stability and environmental benignity.     

g-C3N4/CuO and g-C3N4/Co3O4 nanohybrid structures as efficient electrode materials in symmetric supercapacitors

Metal oxide dispersed graphitic carbon nitride hybrid nanocomposites (g-C₃N₄/CuO and g-C₃N₄/Co₃O₄) were prepared via a direct precipitation method. The materials were used as an electrode material in symmetric supercapacitors. The g-C₃N₄/Co₃O₄ electrode based device exhibited a specific capacitance of 201 F g⁻¹ which is substantially higher than those using g-C₃N₄/CuO (95 F g⁻¹) and bare g-C₃N₄ electrodes (72 F g⁻¹). At a constant power density of 1 kW kg⁻¹, the energy density given by g-C₃N₄/Co₃O₄ and g-C₃N₄/CuO devices is 27.9 W h kg⁻¹ and 13.2 W h kg⁻¹ respectively. The enhancement of the electrochemical performance in the hybrid material is attributed to the pseudo capacitive nature of the metal oxide nanoparticles incorporated in the g-C₃N₄ matrix.

Comparison of electrochemical performance of symmetric supercapacitors based on g-C₃N₄/CuO and g-C₃N₄/Co₃O₄ electrodes.     

The construction of a sandwich structured Co3O4@C@PPy electrode for improving pseudocapacitive storage

Sandwich structured hybrids consisting of a Co₃O₄ nanowire as the core, amorphous carbon (C) as the inner shell and a polypyrrole (PPy) outer layer as the exodermis are synthesized via a hydrothermal method and constant current electropolymerization. The formation mechanism and growth stage of PPy on carbon surfaces is investigated and it was discovered that PPy layer thickness, corresponding to nucleation time of the polymer, as the dynamic factor, can influence the pseudocapacitive properties of the obtained composites. The carbon layer acts as both a network to increase the electric conductivity and a buffer agent to reduce volume expansion of Co₃O₄ during ion insertion/extraction to achieve higher capacitance and better cyclic stability. So for a capacitor, the Co₃O₄@C@PPy electrode delivers a higher areal capacitance of 2.71 F cm⁻² at 10 mA cm⁻² (1663 F g⁻¹ at 6.1 A g⁻¹) and improved rate capability compared to Co₃O₄ and Co₃O₄@C. An asymmetric device is assembled by the Co₃O₄@C@PPy hybrids as a cathode and a relatively high energy density of 63.64 W h kg⁻¹ at a power density of 0.54 kW kg⁻¹ is obtained, demonstrating that the sandwich structured Co₃O₄@C@PPy hybrids have enormous potential for high-performance pseudocapacitors.

The fabrication of sandwich structural CO₃O₄@C@PPy electrode for improving rate capability and areal capacitance.     

Off-stoichiometric Na3−3xV2+x(PO4)3/C nanocomposites as cathode materials for high-performance sodium-ion batteries prepared by high-energy ball milling

Na₃V₂(PO₄)₃ (NVP) is regarded as a promising cathode material for sustainable energy storage applications. Here we present an efficient method to synthesize off-stoichiometric Na_3−3xV_2+x(PO₄)₃/C (x = 0–0.10) nanocomposites with excellent high-rate and long-life performance for sodium-ion batteries by high-energy ball milling. It is found that Na_3−3xV_2+x(PO₄)₃/C nanocomposites with x = 0.05 (NVP-0.05) exhibit the most excellent performance. When cycled at a rate of 1C in the range of 2.3–3.9 V, the initial discharge capacity of NVP-0.05 is 112.4 mA h g⁻¹, which is about 96% of its theoretical value (117.6 mA h g⁻¹). Even at 20C, it still delivers a discharge capacity of 92.3 mA h g⁻¹ (79% of the theoretical capacity). The specific capacity of NVP-0.05 is as high as 100.7 mA h g⁻¹ after 500 cycles at 5C, which maintains 95% of its initial value (106 mA h g⁻¹). The significantly improved electrochemical performance of NVP-0.05 is attributed to the decrease of internal resistance and increase of the Na⁺ ion diffusion coefficient.

Na₃V₂(PO₄)₃ (NVP) is regarded as a promising cathode material for sustainable energy storage applications.