No abstract

Pseudomorphic conversion of metal–organic frameworks (MOFs) enables the fabrication of nanomaterials with well-defined porosities and morphologies for enhanced performances. However, the commonly reported calcination strategy usually requires high temperature to pyrolyze MOF particles and often results in uncontrolled growth of nanomaterials. Herein, we report the controlled alkaline hydrolysis of MOFs to produce layered double hydroxide (LDH) while maintaining the porosity and morphology of MOF particles. The preformed trinuclear M3(μ3-OH) (M = Ni2+ and Co2+) clusters in MOFs were demonstrated to be critical for the pseudomorphic transformation process. An isotopic tracing experiment revealed that the 18O-labeled M3(μ3-18OH) participated in the structural assembly of LDH, which avoided the leaching of metal cations and the subsequent uncontrolled growth of hydroxides. The resulting LDHs maintain the spherical morphology of MOF templates and possess a hierarchical porous structure with high surface area (BET surface area up to 201 m2·g–1), which is suitable for supercapacitor applications. As supercapacitor electrodes, the optimized LDH with the Ni:Co molar ratio of 7:3 shows a high specific capacitance (1652 F·g–1 at 1 A·g–1) and decent cycling performance, retaining almost 100% after 2000 cycles. Furthermore, the hydrolysis method allows the recycling of organic ligands and large-scale synthesis of LDH materials.

Plate-like copper-substituted P2-type Na0.67CuxMn1−xO2 is able to rapidly charge and discharge within 5 minutes while still giving a capacity of about 90 mA h g−1 at a current of 1000 mA g−1.

Porous hierarchical NiMn2O4/C tremella-like nanostructures are obtained through a simple solvothermal and calcination method. As the anode of lithium ion batteries (LIBs), porous NiMn2O4/C nanostructures exhibit a superior specific capacity and an excellent long-term cycling performance even at a high current density. The discharge capacity can stabilize at 2130 mA h g(-1) within 350 cycles at a current density of 1000 mA g(-1). After a long-term cycling of 1500 cycles, the capacity is still as high as 1773 mA h g(-1) at a high current density of 4000 mA g(-1), which is almost five times higher than the theoretical capacity of graphite. The porous NiMn2O4/C hierarchical nanostructure provides sufficient contact with the electrolyte and fast three-dimensional Li(+) diffusion channels, and dramatically improves the capacity of NiMn2O4/C via interfacial storage.

A composite of pyrite FeS2 microspheres wrapped by reduced graphene oxide (FeS2/rGO) has been synthesized by a facile one-step solvothermal method and applied as an anode in lithium ion batteries (LIBs).

S-Doped 2H-MoSe (i.e., 2H-MoSSe) mesoporous nanospheres assembled from several-layered nanosheets are synthesized by sulfurizing freshly-prepared 1T-MoSe nanospheres, and they serve as a robust host material for sodium storage. The sulfuration treatment is found to be beneficial for removing surface/interface insulating organic contaminants and converting the 1T phase to the 2H phase with improved crystallinity and electrical conductivity. These result in significantly enhanced sodium storage performance, including charge/discharge capacity, first Coulombic efficiency, cycling stability, and rate capability. Coupled with benefits from in situ carbon modification and its mesoporous morphology, the 2H-MoSSe (x = 0.22) nanosphere anode can maintain a reversible capacity of 407 mA h g after 100 cycles with no observable capacity fading at a high current density of 2.0 A g. This value is much higher than those of the anode fabricated with the freshly-prepared 1T-MoSe (95 mA h g) and the annealed 2H-MoSe (144 mA h g) samples. As the current density rises from 0.05 to 5.0 A g (100-fold increase), the discharge capacity retention is significantly increased from 39% before sulfuration to 65% after sulfuration. This superior electrochemical performance of the 2H-MoSSe electrode suggests a promising way to design advanced sodium host materials by surface/interface engineering.

The sodium storage performance of layered metal dichalcogenide anodes enhanced through nanostructure engineering, crystal structure modulation, doping/alloying and composite design is systematically reviewed.

A composite of porous CuCo2O4 nanocubes well wrapped by reduced graphene oxide (rGO) sheets has been synthesized by a facile microwave-assisted solvothermal reaction and applied as anode in lithium ion batteries (LIBs). The porous structure of the CuCo2O4 nanocubes not only provides a high surface area for contact with the electrolyte, but also assists by accommodating volume change upon charging-discharging. Impedance measurements and transmission electron microscopy show that incorporation of rGO further decreases the charge transfer resistance and improves the structural stability of the composite. As an anode material for a LIB, the composite exhibits a high stable capacity of ∼ 570 mA h g(-1) at a current density of 1000 mA g(-1) after 350 cycles. With a high specific surface area and a low charge transfer resistance, the composite anode shows impressive performance especially at high current density. The LIB shows a high capacity of ∼ 450 mA h g(-1) even at a high current density of 5000 mA g(-1), demonstrating the composite's potential for applications in LIBs with long cycling life and high power density.