ABSTRACT
Bimetallic sulfide ((Ni0.3Co0.7)9S8) nanoparticles confined by dual-carbon nanostructures are prepared by pyrolyzing a mixture of surfactant-intercalated layered double hydroxide and melamine, and deliver a highly reversible capacity and decent rate capability as anode nanomaterials for lithium- and sodium-ion batteries.
ABSTRACT
Transition-metal sulfides (TMSs) are suggested as promising electrode materials for electrochemical pseudocapacitors and lithium- and sodium-ion batteries; however, they typically involve mixed composites or conventionally stoichiometric TMSs (such as NiCo2S4 and Ni2CoS4). Herein we demonstrate a preparation of solid-solution sulfide (Ni0.7Co0.3)S2 supported on three-dimensional graphene aerogel (3DGA) via a sulfuration of NiCo-layered double hydroxide (NiCo-LDH) precursor/3DGA. The electrochemical tests show that the (Ni0.7Co0.3)S2/3DGA electrode exhibits a capacitance of 2165 F g-1 at 1 A g-1, 2055 F g-1 at 2 A g-1, and 1478 F g-1 at 10 A g-1; preserves 78.5% capacitance retention upon 1000 cycles for pseudocapacitors; and in particular, possesses a relatively high charge capacity of 388.7 mA h g-1 after 50 cycles at 100 mA g-1 as anode nanomaterials for sodium-ion batteries. Furthermore, the electrochemical performances are readily tuned by varying the cationic type of the tunable LDH precursors to prepare different solid-solution sulfides, such as (Ni0.7Fe0.3)S2/3DGA and (Co0.7Fe0.3)S2/3DGA. Our results show that engineering LDH precursors can offer an alternative for preparing diverse transition-metal sulfides for energy storage.
ABSTRACT
Layered double hydroxides (LDHs), also known as hydrotalcite-like anionic clay compounds, have attracted increasing interest in electrochemical energy storage, in the main form of LDH precursor-derived transition metal oxides (TMOs). One typical approach to improve cycling stability of the LDH-derived TMOs is to introduce one- and two-dimensional conductive carbonaceous supports, such as carbon nanotubes and graphene. We herein demonstrate an effective approach to improve the electrochemical performances of well-dispersed biactive NiCo2S4/Ni0.96S as anode nanomaterials for lithium-ion batteries (LIBs), by introducing a three-dimensional graphene aerogel (3DGA) support. The resultant 3DGA supported NiCo2S4/Ni0.96S (3DGA/NCS) composite, obtained by sulfuration of NiCo-layered double hydroxide (NiCo-LDH) precursor in situ grown on the 3DGA support (3DGA/NiCo-LDH). Electrochemical tests show that the 3DGA/NCS composite indeed delivers the greatly enhanced electrochemical performances compared with the NiCo2S4/Ni0.96S counterpart on two-dimensional graphene aerogel, i.e., a high reversible capacity of 965 mA h g-1 after 200 cycles at 100 mA g-1 and especially a superlong cycling stability of 620 mA h g-1 after 800 cycles at 1 A g-1. The enhancements could be ascribed to the compositional and structural advantages of boosting electrochemical performances: (i) well-dispersed NiCo2S4/Ni0.96S nanoparticles with interfacial nanodomains resulting from both the dual surface confinements of the 3DGA support and the crystallographic confinement of NiCo-well-arranged LDH crystalline layer, (ii) an appropriate specific surface area and a wide pore size distribution of mesopores and macropores, and (iii) highly conductive 3DGA support that is measured experimentally by using electrochemical impedance spectra to underlie the enhancement. Our results demonstrate that the tunable LDH precursor-derived synthesis route may be extended to prepare various transition metal sulfides and even transition metal phosphides for energy storage with the aid of tunable cationic type and molar ratio.
