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A hierarchical microstructure constructed with graphitic-carbon-coated Ni3S2 nanoparticles anchored on N-doped mesoporous carbon nanoflakes was fabricated using a nickel-based micro-nano structure as a precursor and polydopamine as a carbon source. By optimizing the microstructure, the obtained Ni3S2/carbon composite compounded with the thickest carbon nanoflakes delivers ultrafast and stable Na-ion storage performance, and can maintain a reversible charge capacity of 372 mA h g-1 at a current density of 5 A g-1 over 250 cycles, and 316 mA h g-1 even at a current density of 20 A g-1 for 2000 cycles. These remarkable electrochemical properties can be attributed to its hierarchical microstructure of graphitic-carbon-coated Ni3S2 particles and N-doped mesoporous carbon nanoflakes, which provide easy accessibility to the electrolyte, fast electron transport and Na+ diffusion, and even relieve the strain caused by the volume expansion upon cycling.

Sodium-ion battery has been considered as an ideal alternative to lithium-ion battery due to the abundant resource of sodium. Hard carbon stands a good chance among most carbons to be the most promising anode material for sodium-ion battery because of its randomly oriented graphite layers. However, the disordered graphite layers display sluggish kinetics of sodium ions thus the high-rate capability of hard carbon in sodium-ion battery is still a big challenge. In this study, extremely ultrafast P-doped carbon nanosheet anode with graphene-like wrinkles and sheet thickness of ca. 8 nm for sodium-ion battery was synthesized by pyrolysis of coal pitch with the assistance of sodium hypophosphite. The ultrathin sheet structure and P-doped property could render pseudocapacitive behavior, as a result, the resultant carbon nanosheet anode delivers high-rate capacity and also the long-term cycling stability (i.e., a high reversible capacity of 189 mA h g−1 at 2 A g−1 after 500 cycles, and an extraordinarily high capacity of 80 mA h g−1 at 20 A g−1 after 10,000 cycles).

A new strategy of using hollow nano-spherical nickel silicate/nickel sulfide composite to stabilize sulfur for lithium-sulfur (Li-S) battery was introduced for the first time. The hollow composite with an accessible mesoporous shell obtained by self-template synthesis can encapsulate ca. 75 wt% sulfur which displays a specific capacity of 640 mAh g−1 after 500 cycles at 0.5 C rate. Furthermore, even at a very high current density of 2.0 C, the discharge capacity remains at a high value of 466 mAh g−1. The long cycling stability and prominent rate performance in Li-S battery can be due to the expedient structure of hollow cavity and mesoporous shell for physisorption and the nickel silicate/nickel sulfide composite for chemisorption of polysulfide.

Fe3O4 is considered to be an ideal substitute for graphite anode due to its high lithium (Li) and sodium (Na) storage capacity, however, its sharp volume change after lithiation/sodiumization and poor electrical conductivity have brought huge challenges to the practical application. In this study, a lamellar Fe3O4-based electrode was constructed via an in-situ plantation of carbon-coated Fe3O4 nanoparticles on the surface of the reduced graphene oxide nanosheet. Owing to the ultra-small carbon-coated Fe3O4 nanoparticles (~12.5 nm) and unique two-dimensional lamellar structure, the obtained sample displays excellent cycle and rate performance in lithium/sodium-ion batteries. A high reversible capacity of 849 mA h g−1 is obtained at 500 mA g−1 after 120 cycles for lithium-ion batteries and a discharge capacity up to 429 mA h g−1 is remained at 100 mA g−1 after 300 cycles for sodium-ion batteries.

Ni3S2 has become a promising anode material for lithium-ion batteries (LIBs) due to its favorable electrochemical conversion reaction, high theoretical specific capacity, and low cost. In this work, a nanoflake-assembled Ni-doped Ni3S2 sheet-like nanocomposite (Ni3S2–Ni–NF) was constructed using graphene oxide as the structure-directing agent by a simple two-step solvothermal reaction. The design of nanoflake subunit, sheet-like morphology, and Ni-doped Ni3S2 nanocomposite gains great promise for the application of LIBs by shortening the diffusion pathway of Li ions, improving the electrical connectivity as well as minimizing the electrode volume strain. As expected, the Ni3S2–Ni–NF nanocomposite exhibited excellent reversible capacities, high rate performance, and satisfactory cycling performance. For instance, reversible specific capacities of 741.8 mA h g−1 and 598.2 mA h g−1 can be retained after 120 cycles at current densities of 200 mA g−1 and 500 mA g−1, respectively. Furthermore, even at a very high current density of 1000 mA g−1, the discharge capacity remained as high as 497 mA h g−1.

Co9S8 is regarded as a promising electrode material for advanced lithium storage (lithium-ion battery (LIB) and lithium-sulfur (Li-S) battery) because of its remarkable electrical conductivity, polar property, and low cost. In this study, three-dimensional nanohybrid assembled by Co9S8 nanocrystal coated hollow carbon nanosphere was synthesized via a low-temperature solution-based sulfidation process. Different from some other hollow Co9S8/carbon structures, the hollow carbon nanosphere embedded inside the Co9S8 crystal would work as a more efficient conductive medium. When used as electrode materials for LIB and Li-S battery, the obtained nanohybrid exhibits excellent lithium storage properties and a distinctly better cycling performance. A discharge capacity of 560 mA h g−1 is obtained after 400 cycles at a current density of 1000 mA g−1 for LIB. Furthermore, for Li-S battery, the obtained Co9S8/carbon hybrid used as sulfur host gave a reversible discharge capacity of ca. 880 mA h g−1 after 400 cycles at a current density of 0.5 C (837.5 mA g−1), corresponding to 87% retention of its initial discharge capacity.