Pseudocapacitive Lithium Storage of Cauliflower-Like CoFe2 O4 for Low-Temperature Battery Operation

Partially Reduced Titanium Niobium Oxide: A High-Performance Lithium-Storage Material in a Broad Temperature Range

The existing electrode materials for lithium-ion batteries (LIBs) generally suffer from poor rate capability at low temperatures, severely limiting their applications in winter and cold climate area. Here, partially reduced TiNb24 O62 (PR-TNO) are reported that demonstrates excellent electrochemical performance in a broad temperature range, notably at low temperatures. Its crystal structure is similar to that of Ti2 Nb10 O29 upon partial reduction in H2 . The titanium and niobium ions in PR-TNO enable multielectron transfer, safe operation, and high Coulombic efficiencies. Benefiting from the increased electronic conductivity of the partially reduced phase and its robust crystal structure with a large interlayer spacing, PR-TNO shows fast electron and Li+ transport, small volume change associated with Li+ storage, and notable capacitive behavior, resulting in good electrochemical performance even at very low temperatures. At -20 °C, a large reversible capacity of 313 mAh g-1 is obtained at 0.1C, reaching 83.3% of that at 25 °C. At 5C, high rate capability (58.3% of that at 0.5C) is achieved, only slightly lower than that at 25 °C (60.7%). Furthermore, PR-TNO demonstrates excellent cyclic stability with 99.2% of the initial capacity after 1680 cycles, confirming its excellent suitability for low-temperature LIBs.

Solventless synthesis of nanospinel Ni1−xCoxFe2O4 (0 ≤ x ≤ 1) solid solutions for efficient electrochemical water splitting and supercapacitance

The formation of solid solutions represents a robust strategy for modulating the electronic properties and improving the electrochemical performance of spinel ferrites. However, solid solutions have been predominantly prepared via wet chemical routes, which involve the use of harmful and/or expensive chemicals. In the present study, a facile, inexpensive and environmentally benign solventless route is employed for the composition-controlled synthesis of nanoscopic Ni_1−xCo_xFe₂O₄ (0 ≤ x ≤ 1) solid solutions. The physicochemical characterization of the samples was performed by p-XRD, SEM, EDX, XPS, TEM, HRTEM and UV-Vis techniques. A systematic investigation was also carried out to elucidate the electrochemical performance of the prepared nanospinels towards energy generation and storage. Based on the results of CV, GCD, and stability tests, the Ni_0.4Co_0.6Fe₂O₄ electrode showed the highest performance for the supercapacitor electrode exhibiting a specific capacitance of 237 F g⁻¹, superior energy density of 10.3 W h kg⁻¹ and a high power density with a peak value of 4208 W kg⁻¹, and 100% of its charge storage capacity was retained after 4000 cycles with 97% coulombic efficiency. For HER, the Ni_0.6Co_0.4Fe₂O₄ and CoFe₂O₄ electrodes showed low overpotentials of 168 and 169 mV, respectively, indicating better catalytic activity. For OER, the Ni_0.8Co_0.2Fe₂O₄ electrode exhibited a lower overpotential of 320 mV at a current density of 10 mA cm⁻², with a Tafel slope of 79 mV dec⁻¹, demonstrating a fast and efficient process. These results indicated that nanospinel ferrite solid solutions could be employed as promising electrode materials for supercapacitor and water splitting applications.

The formation of solid solutions represents a robust strategy for modulating the electronic properties and improving the electrochemical performance of spinel ferrites.