Nanophase ZnCo₂O₄ as a High Performance Anode Material for Li‐Ion Batteries

Abstract

ZnCo2O4 has been synthesized by the low‐temperature and cost‐effective urea combustion method. X‐ray diffraction (XRD), HR‐TEM and selected area electron diffraction (SAED) studies confirmed its formation in pure and nano‐phase form with particle size ∼ 15–20 nm. Galvanostatic cycling of nano‐ZnCo2O4 in the voltage range 0.005–3.0 V versus Li at 60 mA g–1 gave reversible capacities of 900 and 960 mA h g–1, when cycled at 25 °C and 55 °C, respectively. These values correspond to ∼ 8.3 and ∼ 8.8 mol of recyclable Li per mole of ZnCo2O4. Almost stable cycling performance was exhibited in the range 5–60 cycles at 60 mA g–1 and at 25 °C with ∼ 98 % coulombic efficiency. A similar cycling stability at 55 °C, and good rate‐capability both at 25 and 55 °C were found. The average discharge‐ and charge‐potentials were ∼ 1.2 V and ∼ 1.9 V, respectively. The ex‐situ‐XRD, ‐HRTEM, ‐SAED and galvanostatic cycling data are consistent with a reaction mechanism for Li‐recyclability involving both de‐alloying‐alloying of Zn and displacement reactions, viz., LiZn ↔ Zn ↔ ZnO and Co ↔ CoO ↔ Co3O4. For the first time we have shown that both Zn‐ and Co‐ions act as mutual beneficial matrices and reversible capacity contribution of Zn through both alloy formation and displacement reaction takes place to yield stable and high capacities. Thus, nano‐ZnCo2O4 ranks among the best oxide materials with regard to Li‐recyclability.

General Synthesis of Transition Metal Oxide Ultrafine Nanoparticles Embedded in Hierarchically Porous Carbon Nanofibers as Advanced Electrodes for Lithium Storage

“…[48] The anodic curves display two peaks, in which the peak at 0.51 V is related to the multi-step de-alloying process of Li-Zn alloy, and the broad peak at 1.37 V is related to the formation of ZnO according to the redox reaction between Zn and Li 2 O. [49,50] Therefore, the overall reaction process of ZnO UNPs@HPCNFs in LIBs could be described as Equations 1, 2:…”

Thermal evolution of ZnCo2O4 spinel phase in air

“…ZnCo 2 O 4 exhibits a normal spinel structure with Zn II ions in the tetrahedral sites and Co III occupying the octahedral ones. This is attributed to the dominating advantage of placing the d 6 ions in octahedral sites, where adoption of the low-spin configuration gives it a decisively favourable Crystal Field Stabilization Energy. 33) Accordingly the ionic radii of the cationic species in this spinel structure are 0.60 and 0.545 ¡ for the Zn II inferred from DTATG gradually proceeds after the decomposition of the oxalate precursor.…”

“…3), 6) In the same way, solid solutions of nominal composition Zn x Co 3¹x O 4 exhibit improved adsorbent capabilities so they find application as selective catalysts for oxidation and hydrogenation reactions, 7) as well as for the monitoring and removal of harmful species such as Cl 2 , NO 2 , CO 2 and H 2 S among others. 8)10) Finally in the last years its magnetic behaviour, either as a single compound or as an impurity phase in the Zn 1¹x Co x O system, is under investigation in the field of room temperature ferromagnetic diluted semiconductors for spintronic applications.…”

Local structure and magnetism of Co3+ in wurtzite Co:ZnO

“…Many avenues have been followed to accomplish these objectives, and several mechanisms, such as defects [4] or carrier mediation [5], have been proposed to explain the occasional observations of long-range magnetic order, often based on large hole concentrations [6] or oxygen vacancies in doped ZnO [7]. For ZnCo 2 O 4 , on the other hand, which is widely known as anode material in lithium batteries [8] and as crystalline, or amorphous p-type gate in junction field-effect transistors [9], it has also been reported that the provided oxygen partial pressure during growth can change the conduction type and even the magnetic properties from paramagnetic to ferromagnetic [10]. Other studies, however, observed weak antiferromagnetism at low temperatures when no extra oxygen is provided [11,12].…”