Rapid low-temperature synthesis of mesoporous nanophase ZnFe₂O₄with enhanced lithium storage properties for Li-ion batteries

Abstract

In this work, a rapid low-temperature and cost-effective refluxing synthesis strategy was elegantly designed, and elaborately developed for high-yield fabrication of mesoporous nanocrystalline ZnFe 2 O 4 with nanoscaled size of $7 nm, desirable mesoporosity and large specific surface area. Benefitting from these admirable nanostructured architectures, the as-derived nanophase ZnFe 2 O 4 exhibited excellent discharge capacity of 1322 mA h g À1 on the first cycle, and showed outstanding cycling durability, rate capability, and coulombic efficiency even at high current rates when evaluated as an anode for Li-ion batteries. More importantly, a low temperature of 100 C and short reaction time of 5 h were applied here; therefore, the efficient synthetic strategy we proposed herein is advocated for scaled-up commercial application.

Green Template‐Free Synthesis of Hierarchical Shuttle‐Shaped Mesoporous ZnFe2O4 Microrods with Enhanced Lithium Storage for Advanced Li‐Ion Batteries

“…As the voltage declines gradually up to the 0.01 V, a whole initial discharge capacity of ∼1520 mAh g −1 (corresponding to ∼13.7 moles of Li per ferrite formula) is delivered, which should be associated with further reduction, the formation of Li–Zn alloy and the irreversible decomposition of the solvent in the electrolyte to form solid electrolyte interface (SEI) on the anode surface 43. In view of the first charge capacity for ∼1150 mAh g −1 (release of ∼10.4 moles of Li per ZnFe 2 O 4 ), the corresponding initial CE is thus calculated as ∼76 %, which is higher than those for yolk‐shell structured ZnFe 2 O 4 (∼74 %),9 ZnFe 2 O 4 NPs (∼71 %),15 ZnFe 2 O 4 /graphene (∼68.6 %,44 61.6 %45), ZnFe 2 O 4 hollow microspheres (∼71 %),43 ZnFe 2 O 4 microcubes (∼72 %),6 ZnO/ZnFe 2 O 4 microcubes (∼70 %)6 and ZnO/ZnFe 2 O 4 /C octahedral (∼75.6 %) 5. The enhanced CE for the ZnFe 2 O 4 MRs might be attributed to good structural stability of the MRs, and the increased reversibility of the involved electrochemical reactions,9, 46, 47 which is also confirmed by the CV measurement (Figure 7).…”

“…Recently, mixed transition‐metal oxides (MTMOs) with spinel structures such as AB 2 O 4 (A=Zn, Ni, Cu; B=Co, Mn, Fe) have been extensively exploited as emerging anode materials for LIBs, benefiting from their larger reversible capacities determined by the complex compositions and intrinsically synergetic effect, and higher safety when compared to the commercialized graphite‐based anodes 5–13. Remarkably, ternary spinel zinc ferrite (ZnFe 2 O 4 ), in which divalent (Zn 2+ ) ions and trivalent (Fe 3+ ) ions occupy tetrahedral (A) and octahedral (B) sites represented as (Zn 1– x 2+ Fe x 3+ )[Zn x 2+ Fe 2– x 3+ ] (see Figure 1),14 stands out from these appealing ferrites, and is established as a competitive anode material for next‐generation LIBs,5, 6, 9, 15, 16 in view of its low price, abundance, nontoxicity, and the environmental friendliness of both Zn and Fe species. Furthermore, the elegant combination of the “de‐alloying–alloying” and “conversion” reactions of “LiZn‐Fe‐Li 2 O composite” for reversible lithium storage is generally observed for the ZnFe 2 O 4 , in which Fe and Zn react with Li 2 O to absorb/release Li during lithiation/de‐lithiation, and Li + further forms an alloy with Zn and de‐alloy meanwhile, generating a large theoretical capacity of ∼1072 mAh g −1 3.…”

“…Motivated by the pioneer application of nano‐ZnFe 2 O 4 and Ag‐doped ZnFe 2 O 4 thin films as anodes for LIBs,18 to date, intriguing ZnFe 2 O 4 structures with diverse nanoarchitectures, including nanofibers (NFs),19 nanocrystals,15, 20, 21 nano‐octahedrons,22 nanoneedles,23 nanowires,24 nanospheres,25 etc., have been extensively synthesized and utilized as promising anodes for high‐performance LIBs, thanks to their attractive features favoring efficient Li‐storage behaviors, as reported before 3. 15, 19–27 However, there are still some obstacles to the practical use of nanostructured anodes, and several repugnant drawbacks cannot be ignored at all, such as poor reproducibility, in‐homogeneity, high fabrication costs due to sophisticated synthetic techniques, an increase in solid‐electrolyte interfacial (SEI) layer area leading to modest Coulombic efficiency (CE), lower packing density resulting from lower volumetric energy density, and so on, which go against their practical applications 3. 19 Encouragingly, hierarchical micro‐/nanostructures of micrometer dimensions but internally consisting of nanobuilding blocks render a fascinating avenue to circumvent the aforementioned flaws well 3.…”

Dopant-induced shape evolution of polyhedral magnetite nanocrystals and their morphology/component-dependent high-rate electrochemical performance for lithium-ion batteries

“…In this case, consequently, the fragmented nanoparticles would offer larger reaction interfacial area and render a larger utilization of electrode materials during and aer the initial cycle, which should be responsible for the good long cycle performance of Mn 0. 6 cubes, which shows no relationship to the original exposed facets as the morphology was already destroyed during cycles. Based on the previous works on the electrochemical reversibility of metal oxides, the enhanced cycle stability of Mn 0.6 Fe 2.4 O 4 octahedrons may be ascribed to the great reversibility of MnO within the Mn x Fe 3Àx O 4 spinel.…”

“…Furthermore, aer the deep charge/discharge for 10 cycles at 4 A g À1 , a high capacity of 906.6 mA h g À1 (7.8 moles of Li + ) is recovered over 10 cycles at 0.5 A g À1 as a result of reduced electrochemical polarization, indicating stable kinetic features and good reversibility of Mn 0. 6 cuboctahedrons deliver much lower specic capacities of 768.0-423.6 mA h g À1 (6.6-3.7 moles of Li + ) at current rates of 1-4 A g À1 and 735.5 mA h g À1 (6.4 moles of Li + ) aer the extended 10 cycles at 0.5 A g À1 as a result of inefficient electron and lithium-ion transportation in Mn 0.3 Fe 2.7 O 4 cuboctahedrons. As for Fe 3 O 4 cubes, the reversible capacity continuously decayed with cycling, and exhibited a capacity as low as 218.9 mA h g À1 (1.9 moles of Li + ) at the current density of 4 A g À1 and 512.8 mA h g À1 (4.4 moles of Li + ) aer the 10 cycles at 0.5 A g À1 .…”