Abstract
Lithium-ion (Li-ion) batteries have been widely used in various kinds of electronic devices in our daily life. The use of aqueous electrolyte in Li-ion battery would be an alternative way to develop low cost and environmentally friendly batteries. In this paper, the lithium iron phosphate (LiFePO4) thin film cathode for the aqueous rechargeable Li-ion battery is prepared by radio frequency magnetron sputtering deposition method. The XRD, SEM, and AFM results show that the film is composed of LiFePO4 grains with olivine structure and the average size of 100 nm. Charge-discharge measurements at current density of 10 μAh cm−2 between 0 and 1 V show that the LiFePO4 thin film electrode is able to deliver an initial discharge capacity of 113 mAh g−1. Specially, the morphological changes of the LiFePO4 film electrode during charge and discharge processes were investigated in aqueous environment by in situ EC-AFM, which is combined AFM with chronopotentiometry method. The changes in grain area are measured, and the results show that the size of the grains decreases and increases during the charge and discharge, respectively; the relevant mechanism is discussed.
Highlights
With the wide utilization of portable electrical devices and the growing demand for new energy, the development of high-performance and environmentally friendly energy storage devices is becoming increasingly important
The electrochemical performance of the LiFePO4 powder and the film were characterized by cyclic voltammetry with a three-electrode system in 1 M Li2SO4 aqueous electrolyte
The appearance of well-defined pair redox peaks shows the redox activity of Fe2+/Fe3+, which is caused by lithium ion insertion/extraction in LiFePO4 during charge and discharge processes
Summary
With the wide utilization of portable electrical devices and the growing demand for new energy, the development of high-performance and environmentally friendly energy storage devices is becoming increasingly important. Major drawbacks of the organic electrolyte are obvious such as (a) when the battery is discarded, the electrolyte may leak into the land and cause environmental problems [4, 5]; and (b) the electrolyte makes the manufacture process of the battery more complicated and expensive. For these reasons, the use of aqueous electrolyte in Li-ion battery would be an alternative way to develop low cost and environmentally friendly batteries [6]. The electrochemical performance of LiFePO4 as a cathode in aqueous rechargeable Li-ion battery (ARLB) has been studied. It has been reported that in aqueous electrolyte, the estimated average discharge capacity for 20 cycles is about 29 μAh cm−2, while it is
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