Low-content SnO2 nanodots on N-doped graphene: lattice-confinement preparation and high-performance lithium/sodium storage

Rational construction of nanosized anode nanomaterials is crucial to enhance the electrochemical performance of lithium-/sodium-ion batteries (LIBs/SIBs). Various anode nanoparticles are created mainly via templating surface confinement, or encapsulation within precursors (such as metal-organic frameworks). Herein, low-content SnO₂ nanodots on N-doped reduced graphene oxide (SnO₂@N-rGO) were prepared as anode nanomaterials for LIBs and SIBs, via a distinctive lattice confinement of a CoAlSn-layered double hydroxide (CoAlSn-LDH) precursor. The SnO₂@N-rGO composite exhibits the advantagous features of low-content (17.9 wt%) and uniform SnO₂ nanodots (3.0 ± 0.5 nm) resulting from the lattice confinement of the Co and Al species to the surrounded Sn within the same crystalline layer, and high-content conductive rGO. The SnO₂@N-rGO composite delivers a highly reversible capacity of 1146.2 mA h g^-1 after 100 cycles at 0.1 A g^-1 for LIBs, and 387 mA h g^-1 after 100 cycles at 0.1 A g^-1 for SIBs, outperforming N-rGO. Furthermore, the dominant capacitive contribution and the rapid electronic and ionic transfer, as well as small volume variation, all give rise to the enhancement. Precursor-based lattice confinement could thus be an effective strategy for designing and preparing uniform nanodots as anode nanomaterials for electrochemical energy storage.

Three-dimensional mesoporous sandwich-like g-C3N4-interconnected CuCo2O4 nanowires arrays as ultrastable anode for fast lithium storage

Inspite of their impressive high theoretical capacity as Lithium-ion batteries (LIBs) anodes, spinel transition-metal oxides (TMOs) suffer serious volume expansion, aggregation and the pulverization of crystal structures during lithiation/delithiation, and this process severely restrict their industrial application. Multi-dimensional morphological engineering of spinel TMO nanostructures is an effective way to solve this issue. In this work, using facile hydrothermal synthetic methods, spinel CuCo₂O₄ nanowires arrays are synthesized and supported on g-C₃N₄ nanosheets, thus forming a unique sandwich-like interconnected three-dimensional mesoporous structure containing high amount of void spaces. Addition of g-C₃N₄ nanosheets to CuCo₂O₄ nanowire arrays may shorten the Li⁺ diffusion distance and electron transfer pathway, and may also provide more active sites for Li⁺ diffusion into electrolyte and buffer for the volume expansion and aggregation of CuCo₂O₄. As a LIB anode material, CuCo₂O₄@g-C₃N₄ shows initial lithiation capacity of 840.6 mAh g^-1, and capacity retention of 641.2 mAh g^-1 after 60 cycles at the current density of 0.1 A g^-1 and 499.2 mAh g^-1 after 40 cycles at high current of 1 A g^-1, which is significantly better than value of pure CuCo₂O₄ nanowires. This work affords a new way to tackle the problem of volume expansion of high capacity spinel TMO anode materials using g-C₃N₄ nanosheets as buffering agent.

Solid-Solution Sulfides Derived from Tunable Layered Double Hydroxide Precursors/Graphene Aerogel for Pseudocapacitors and Sodium-Ion Batteries

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 (Ni_0.7Co_0.3)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 (Ni_0.7Co_0.3)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 (Ni_0.7Fe_0.3)S₂/3DGA and (Co_0.7Fe_0.3)S₂/3DGA. Our results show that engineering LDH precursors can offer an alternative for preparing diverse transition-metal sulfides for energy storage.

Effect of cobalt alloying on the electrochemical performance of manganese oxide nanoparticles nucleated on multiwalled carbon nanotubes

MnO is an electrically insulating material which limits its usefulness in lithium ion batteries. We demonstrate that the electrochemical performance of MnO can be greatly improved by using oxygen-functional groups created on the outer walls of multiwalled carbon nanotubes (MWCNTs) as nucleation sites for metal oxide nanoparticles. Based on the mass of the active material used in the preparation of electrodes, the composite conversion-reaction anode material Mn_1-x Co _x O/MWCNT with x = 0.2 exhibited the highest reversible specific capacity, 790 and 553 mAhg^-1 at current densities of 40 and 1600 mAg^-1, respectively. This is 3.1 times higher than that of MnO/MWCNT at a charge rate of 1600 mAg^-1. Phase segregation in the [Formula: see text] nanoparticles was not observed for x ≤ 0.15. Capacity retention in x = 0, 0.2, and 1 electrodes showed that the corresponding specific capacities were stabilized at 478, 709 and 602 mAhg^-1 respectively, after 55 cycles at a current density of 400 mAg^-1. As both MnO and CoO exhibit similar theoretical capacities and MnO/MWCNT and CoO/MWCNT anodes both exhibit lower performance than Mn_0.8Co_0.2O/MWCNT, the improved performance of the [Formula: see text] alloy likely arises from beneficial synergistic interactions in the bimetallic system.

Triple-Confined Well-Dispersed Biactive NiCo2S4/Ni0.96S on Graphene Aerogel for High-Efficiency Lithium Storage

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/Ni_0.96S as anode nanomaterials for lithium-ion batteries (LIBs), by introducing a three-dimensional graphene aerogel (3DGA) support. The resultant 3DGA supported NiCo₂S₄/Ni_0.96S (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/Ni_0.96S 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/Ni_0.96S 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.