Ordered LiFe5O8 thin films prepared by pulsed laser deposition as an anode material for all-solid thin film batteries

Abstract

The search for obtaining a Co free low-cost and high-capacity anode thin film material for high energy density all-solid thin film batteries has been driving the increasing innovation and research in Li-ion battery (LIB) technology. In the present case, LiFe5O8 (LFO) thin films are prepared by pulsed laser deposition (PLD) technique and their electrochemical properties, Li ion dynamics, conducting processes at various frequencies and current rates are explored. LFO thin films are seen to crystallize in ordered alpha-phase with an inverse spinel structure. Chemical state of all the elements is analysed using X-ray photoelectron spectroscopy method. Cyclic voltam-meter (CV) study carried out between 0-3 V shows the reduction peak at 0.76 V initially and in the later cycles at 0.86 V with a small shift depicting the exact conversion type behaviour of the LFO thin film. LFO thin film exhibits specific discharge capacity of 25 mu Ah/cm2 at 10 mu A/cm2 current density during the first cycle. Rate capability measurements are carried out at various current densities of 10, 20, 30, 40, 50 and 10 mu A/cm2. Li-ion diffusion coefficient during the de-lithiation and lithiation process is seen to be 3.78 x 10-14 cm2/s and 1.41 x 10-13 cm2/s, respectively. CV studies at various scan rates indicates that the mechanism of Li+ storage is dominated by a diffusion-controlled process at low scan rates and with increasing scan rate it becomes a surface-controlled process. Electrochemical impedance studies at various frequencies shows the decrease in charge transfer resistance with increasing cycles. Combined structural, chemical, electrochemical and impedance studies of LFO thin films indicates that these films can be employed for fabricating Co and Ni free all-solid thin film Li -ion batteries for energy storage applications.