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Two-dimensional calcium terephthalate flakes with a thickness of 100–300 nm have been synthesized via adjusting the water : ethanol volume ratio in the solvothermal method. As anodes for sodium-ion batteries, 2D sheet electrodes possess fast kinetics and thus display superior cycling capacity and high-rate capability (195 mA h g−1 at 1000 mA g−1). [ABSTRACT FROM AUTHOR]

Abstract Comparative studies have been made to investigate the influence of different synthesis routes on the structural, microstructural, magnetic and magnetostrictive properties of cobalt ferrite, using spent Li-ion batteries as raw materials. Three routes are proposed in this study, mainly, sol-gel, co-precipitation and microwave assisted hydrothermal methods. X-ray diffraction patterns of the samples confirmed the formation of pure phase cubic spinel structure with Fd-3m space group. It is observed that the synthesis methods have a strong influence on the morphological features of the synthesized cobalt ferrite (CoFe 2 O 4) nanoparticles and the fractured surface of the sintered cylindrical rods. Quantitative analysis, based on X-ray photoelectron spectroscopy, indicated that CoFe 2 O 4 had a mixed spinel structure. Magnetic parameters, such as saturation magnetization and coercivity, showed significant differences that were correlated with the different cation distribution, crystallite size and induced lattice strain. This study provides an alternative way for recovering Co from spent Li-ion batteries. The product of this process (cobalt ferrite) obtained through different methods has different magnetostrictive coefficients and strain derivatives, suggesting the potential application in the field of magnetostrictive sensors or actuator devices. [ABSTRACT FROM AUTHOR]

Abstract In this study, we investigated the effects of substituting Li+ for Co2+ at the B sites of the spinel lattice on the structural, magnetic and magnetostrictive properties of cobalt ferrites. The Li+ substituted cobalt ferrites, Co 1-x Li x Fe 2 O 4 , with x varying from 0 to 0.7 in 0.1 increments, were synthesized with a sol-gel auto-combustion method using the cathode materials of spent Li-ion batteries. X-ray diffraction analysis revealed that all the Co 1-x Li x Fe 2 O 4 nanopowders had a single-phase spinel structure and the lattice parameters decreased with increasing Li+ content, which can be proved by slight shifts towards higher diffraction angle values of the (311) peak. Field emission scanning electron microscopy was used to observe the fractured inner surface of the sintered cylindrical rods and the increased porosity resulted in a decreased magnetostriction. The oxidation states of Co and Fe in the cobalt ferrite samples were examined by X-ray photoelectron spectroscopy. High resolution transmission electron microscopy micrographs showed that most particles were roughly spherical and with sizes of 25–35 nm. Li+ substitution had a strong effect on the saturation magnetization and coercivity, which were characterized with a vibrating sample magnetometer. The Curie temperature was reduced due to the decrease in magnetic cations and the weakening of the exchange interactions. The magnetostrictive properties were influenced by the incorporation of Li+ at the B sites of the spinel structure and correlated with the changes in porosity, magnetocrystalline anisotropy and the cation distribution. [ABSTRACT FROM AUTHOR]

This study presents the effect of Er 3+ substitution for Fe 3+ at low concentrations on the structural, magnetic, and magnetostrictive properties of cobalt ferrite synthesized by sol–gel method using spent Li-ion batteries as raw materials. The XRD results confirm the formation of pure-phase cubic spinel structure with average crystallite sizes of 24.8–41.5 nm as obtained through the Scherrer formula. Although Er 3+ substitution does not show any observable changes in morphology, the magnetic and magnetostrictive properties are strongly affected. Density measurements obtained by the Archimedes method reveal that the bulk density decreases and the porosity increases with Er 3+ substitution because of the formation of intragranular pores during sintering. The saturation magnetization and coercivity of the samples obtained with a vibrating sample magnetometer are influenced by the incorporation of Er 3+ at the B-sites. Magnetostriction and strain derivative curves show that Er 3+ substitution makes cobalt ferrite more suitable for advanced magnetomechanical stress sensors and energy-efficient actuator devices. [ABSTRACT FROM AUTHOR]

Cobalt ferrite (CoFe 2 O 4) nanoparticles are synthesized by sol-gel method using spent LiCoO 2 batteries as raw materials successfully. The CoFe 2 O 4 nanoparticles are subsequently coated with N-doped carbon by the carbonization of polydopamine obtained through self-polymerization of dopamine. The N-doped carbon layers with different thickness does not affect the structure and microstructure of CoFe 2 O 4 and they are coated on the surface of CoFe 2 O 4 nanoparticles confirmed by transmission electron microscopy. CoFe 2 O 4 /NC 30 exhibited superior electrochemical performance, such as high specific capacity (919.6 mAh/g for initial cycle at 0.1 A/g), excellent cycling performance (662.9 mAh/g after 200 cycles at 0.1 A/g) and rate capability (357.9 mAh/g at 2 A/g) for using as anodes in lithium-ion batteries compared with pristine CoFe 2 O 4 and other CoFe 2 O 4 /NC nanocomposites. The improved electrochemical performance could be ascribed to enhanced electrical conductivity and structural stability aroused by the N-doped carbon layers. • CoFe 2 O 4 /NC nanocomposites have been synthesized using spent LIBs as raw materials successfully. • The polydopamine derived N-doped carbon layer helps to improve electrochemical performance of CoFe 2 O 4 /NC nanocomposites. • The N-doped carbon layer does double duty: buffer layer and conductive agent. • This procedure provides a novel insight for broadening the recycling path of spent LIBs. [ABSTRACT FROM AUTHOR]

• Co 1+ x Fe 2−2 x /3 O 4 were synthesized by a convenient method using spent LIBs. • This process can reduce environmental pollution and alleviate resource shortage. • Co 1+ x Fe 2−2 x /3 O 4 (x = 0.15) is a candidate for magnetostrictive sensing applications. A series of Co 1+ x Fe 2−2 x /3 O 4 (x = 0, 0.05, 0.1, 0.15, 0.2) samples, in which Fe3+ was progressively replaced by Co2+, were prepared through the sol-gel auto-combustion method using spent Li-ion batteries as raw materials. The structure, morphology, magnetic and magnetostrictive properties of the samples were studied. The purpose of the present work is to make cobalt ferrite more suitable for its application in non-contact sensors and actuators. X-ray diffraction (XRD) patterns show that all the samples have a pure single-phase cubic structure. The non-stoichiometric cobalt ferrite has different crystallite size and lattice constant compared with pure CoFe 2 O 4. Field emission scanning electron microscopy (FE-SEM) was carried out to investigate the amount and size of pores in the sintered samples. The cationic oxidation state and cation distribution of the spinel structure was investigated by means of X-ray photoelectron spectroscopy (XPS). The variations in structure and morphology were found to lead to significant changes in the magnetic and magnetostrictive properties. With the increase of cobalt content, the saturation magnetization and the maximum magnetostrictive coefficient of the samples initially increase and then decrease. Given the different behaviors of the magnetostriction coefficient and strain sensitivity of the samples, their magnetostrictive performance was quantified through a "figure of merit" defined as the product between the two above mentioned parameters. [ABSTRACT FROM AUTHOR]