Pseudocapacitance of Mesoporous Spinel-Type MCo₂O₄ (M = Co, Zn, and Ni) Rods Fabricated by a Facile Solvothermal Route

Abstract

We present the structural properties and electrochemical capacitance of mesoporous MCo 2 O 4 (M = Co, Zn, and Ni) rods synthesized by a facile solvothermal route without necessity to use templates. The Brunauer–Emmett–Teller specific surface areas of these mesoporous rods are found to be about 24, 54, and 62 m 2 g –1 with major pore diameters of about 31, 15, and 9 nm for MCo 2 O 4 , M = Co, Zn, and Ni, respectively. X-ray photoelectron spectroscopy and X-ray diffraction studies reveal the phase purity of the samples with a predominant spinel-type crystal structure. The spinel crystal structure with lattice parameters of 8.118, 8.106, and 8.125 Å is obtained for MCo 2 O 4 , M = Co, Zn, and Ni, respectively. The transmission electron microscopy study reveals that the mesoporous rods are built by self-assembled aggregates of nanoparticles which are well-interconnected to form stable mesoporous rods. The electrochemical capacitor performance was investigated by means of cyclic voltammetry, galvanostatic charge/discharge cycling, and impedance spectroscopy in a three-electrode configuration. As a result, the spinel-type MCo 2 O 4 rods exhibit high specific capacitances of 1846 F g –1 (CoCo 2 O 4 ), 1983 F g –1 (ZnCo 2 O 4 ), and 2118 F g –1 (NiCo 2 O 4 ) at a scan rate of 2 mV/s. Furthermore, the mesoporous spinel-type metal oxides show desirable stability in alkaline electrolyte during long-term cycling with excellent cycling efficiency.

Spinel to Rock-Salt Transformation in High Entropy Oxides with Li Incorporation

“…As expected, Mg in the non-lithiated and lithiated HEO-2 (with Mg 1s binding energies of 1303.4 and 1303.7 eV, respectively) was present as Mg 2+ (Figure 3b) [39,40]. Identification of the Ni oxidation state solely on the basis of the Ni 2p peak is challenging [34][35][36][37][38][41][42][43][44]. However, an overlay of all Ni 2p spectra ( Figure S1) of HEO-1 and HEO-2 revealed only minor differences among the lithiated and non-lithiated materials.…”

“…Co in the non-lithiated HEO-1 was present as Co 2+ (87% of total Co, from the characteristic Co 2+ satellite peak at 786.4 eV). In contrast, for Li(NiFeMnCrCo)O (x = 1), Co was in the oxidation state +3 (Figure 3a) [34][35][36][37][38]. As expected, Mg in the non-lithiated and lithiated HEO-2 (with Mg 1s binding energies of 1303.4 and 1303.7 eV, respectively) was present as Mg 2+ (Figure 3b) [39,40].…”

Surface analytical approaches to reliably characterize lithium ion battery electrodes

“…Finally, a mixed oxidation state of Mn 4+ and Mn 3+ with a 1.6:1 ratio could be proved for Mn in NMC and similarly a Co 2+ to Co 3+ ratio of 5.5:1, whereas Ni only appears in the Ni 2+ state. In a first attempt, we already applied our approach to characterize mesoporous spinel‐type MCo 2 O 4 materials (M = Co, Zn, and Ni) …”

Multi-anionic and -cationic compounds: new high entropy materials for advanced Li-ion batteries

“…The peak at 1303.8 eV in the Mg 1s spectrum can be attributed to Mg 2+ , 48,49 and the Zn 2p 3/2 at 1021.3 eV and Zn LMM at 988.6 eV are indicative of Zn 2+ . [50][51][52] 'NaCl' has also been successfully added to the HEO structure through an identical ball-milling approach. Because the ionic radius of Cl À is much larger than that of O 2À or F À , and Na + is larger than Li + (Cl À = 1.81 Å, O 2À = 1.40 Å, F À = 1.33 Å, Na + = 1.02 Å, Li + = 0.76 Å), 22 it is more difficult to achieve an entropystabilized single-phase structure.…”