The electrode products of rechargeable lithium-ion batteries are the main problem for the energy-saving industry. The intermediate metal oxides must wait for secondary lithium batteries 1–3. Lithium ferrite is an important transition metal oxide with the advantage of low costs, environmental compatibility and ease of production 4, 5. It has been widely studied for various technological applications, such as components of microwave devices and potential cathode materials in lithium-ion batteries 6-10. The alloy and conversion mechanism electrode materials often have a much higher specific capacity than the intercalation electrode materials. Supercapacitors can provide higher power density and superior healing capacity than rechargeable batteries 3. LiFe2O4 is an inverse spinel oxide with Li1+ and three fifths of Fe3+ ions in vivo at the octahedral B sites of the cubic spinal structure of the general formula AB2O4. LiFe2O4 nanoparticles can be synthesized by various chemical methods, such as ball milling mothed 6, citrate-gel method 7, spray pyrolysis 8, aerosol method 9, mechano chemically method 10, and sol gel method 11. For all methods, the sol-gel method is better for synthesis to achieve a smaller grain size, homogeneity and better connectivity. In this work, we attempt to synthesize nanocrystalline lithium ferrite by using a sol-gel method along with citric acid as a chelating agent.
2. Experimental Details
2.1 Materials and Method
The LiFe2O4 nanoparticles were synthesized with the Sol-Gel method. All chemical reagents were purchased from Merck (grade AR) with 99% purity and used without any other purification for the synthesis of LiFe2O4 nanoparticles. 12. 0.1M Li (NO3)2 .6H2O, 0.2M Fe (NO3)2 .9H2O and 0.29 M of citric acid (C6H8O7) were dissolved in 50 ml of de-ionized water separately. Then the solution was added one by one respectively. The solution was stirred at 650 rpm. Then, the dissolved solution was stirred for 6 hours at 70 °C and a brown precipitate formed. The precipitate was then dried in the oven to form the LiFe2O4 powder at 100 °C for 2 hours and calcined at different temperatures of 600 °C, 700 °C, 800 °C, 900 °C and 1000 °C.
2.3. Characterization techniques
TG/DT analysis was carried out using the instrument NETZSCH—STA 449 F3 JUPITER. The Crystalline phase of the LiFe2O4 nanoparticles were identified by X-ray diffraction (XRD) technique using PW3040/60 X’pert PRO powder X-ray diffractometer with CuK? radiation (? = 1.5406 ?) at 40 kV and 30 mA. The step scans were recorded for 2h values in the angular range of 10 ?C to 80 ?C with a scanning speed of 10 min-1. The average diameter of the crystals was calculated using the Debye-Scherer formula
D = K?/?Cos?
Where, D is the crystallite size,
K= (0.9) is a constant related to the shape of the crystal,
? is the wavelength of the radiation employed,
? is full width at half maximum (FWHM) of the obtained characteristic peak in radians and ? is the Bragg diffraction angle. IR spectroscopic measurements were done on a Shimadzu FT-IR 8201PC infrared spectrometer. In order to show the degradation behaviour of the as-prepared sample, FE-SEM system which have been used for morphology and size determination was performed using JEM 2100F. Diffuse reflectance spectrascopy (DRS) measurements of the synthesized samples are recorded in the range of 300–1100 nm using Hitachi 330 UV-VIS spectrometer. An electrochemical property of the nanoparticles was investigated by cyclic voltammetry (CV) model CHI 660.
3. Results and discussions
3.1 TG/DT analysis
Fig.1 TG/DT analysis of LiFe2O4 nanoparticles
Thermogravimetric (TG) and differential thermal (DT) analyzes of the LiFe2O4 nanoparticles prepared from 35 °C to 1100 °C were performed. The TG / DT analysis curves of the lithium ferrite sample are shown in Fig.1. There are three major weight losses that the TG analyzes were observed within this range of 35 ?C to 1100 ?C. The first stage of weight loss is observed at a temperature below 173 ° C (31%) due to water desorption. The second weight loss is expected in the range of 174 ?C to 337 ?C (21%) after the decomposition of the organic models. The final weight loss of 338 ?C to 556 ?C due to the crystallizations of the final product. No weight loss is found above 556 ?C, indicating the formation of LiFe2O4 nanoparticles. From the DTA curve it is observed that the small endothermic peak at 139 °C due to dehydration water. The exothermic peak at 103 ?C, 277 ?C and 400 ?C is attributed due to the decomposition of nitrates and initiates the crystallization formation of lithium ferrite 13. Therefore, after dehydration, the anhydrous precursor passes through the decomposition to produce lithium ferrite. The endothermic peak at 332 ?C and 561 ?C corresponds to the complete decomposition of the citrate precursor to form the lithium ferrite with the simultaneous evolution of CO, CO and acetone molecules formed. A similar conclusion was drawn by Dey et al., 14 for the preparation of lithium ferrite particles synthesized with the sol-gel method.