Electroactive LixFeyOz materials prepared by steam annealing and electrochemical Li insertion

In the present work LixFeyOz was prepared by steam annealing and electrochemical lithium insertion for possible use in Li-ion batteries. In the first step, iron hydroxide is synthesized by chemical precipitation method using FeCl3 and NaOH as starting materials. Iron oxides have been synthesized via steam annealing of Fe(OH)3. Samples have been annealed in steam atmosphere at 750°C and 850°C for 2h. The produced materials were confirmed as magnetite (Fe3O4) by X-ray diffraction method.In a next step, a mixture of magnetite, graphite, acetylene black and PTFE were well mixed and pressed to shape a ring. Resulting composites were subjected to the H+/Li+ ion-exchange in an aqueous LiOH solution to produce lithium iron oxide (LixFeyOz). The bath temperature was hold constant at 70°C and the amount of charge passed through the oxide material was limited in each case to 800 mAh/g. X-ray diffraction analysis revealed that after lithium insertion, the annealed material at 850°C is transformed into the spinel LiFe5O8 phase. Results of charge/discharge cycling showed that lithium insertion has a beneficial effect on electrochemical capacities. Indeed, the sample synthesized at 850oC (E850) showed the highest discharge capacity among other materials. According to SEM, the particle size of the latter has been increased in compare to sample oxidized at 750oC (E750). Compared to the latter, the crystallinity of E850 being enhanced with more pronounced edges and apexes.

Keywords:

Lithium-ion batteries , Lithium insertion , Hydrothermal-electrochemical synthesis method