Abstract
Maghemite nanoparticles were successfully synthesized via a co-precipitation method and electrochemical-optical properties of three different sizes were studied. Using this material as a Li-ion battery cathode, the results of charge–discharge tests showed that decreasing the maghemite particle size increased the lithium hosting capacity. First discharge capacities for cathodes made of material of particle size 11 and 19 nm were 206 and 186 mAh g−1 respectively, while for micron-sized cathode material a discharge capacity of 26 mAh g−1 was obtained. Electrochemical impedance spectroscopy (EIS) was used to derive equivalent circuit elements, which confirmed a reduction in lithium insertion resistance for material with a smaller particle size. EIS investigations disclosed that the Rct and ZW reduced with reduction of particle size, which indicates cathode material with lower particle size is more suitable. Band-gaps of the materials were determined using the diffuse reflectance spectroscopy technique on the base of Kubelka–Munk theory. The results showed that the needed energy for electron conduction reduces with reduction of particle size, which results in capacity enhancement.
Highlights
IntroductionThere are many different energy storage systems amongst which lithium-ion batteries are one of the best candidates
Sources of renewable energy are intermittent and require efficient energy storage
Electrochemical impedance spectroscopy (EIS) was used to derive equivalent circuit elements, which confirmed a reduction in lithium insertion resistance for material with a smaller particle size
Summary
There are many different energy storage systems amongst which lithium-ion batteries are one of the best candidates. One of the challenges for making high capacity Li-ion batteries is the cathode material with transition metal oxides being one of the attractive candidates [1, 2]. Amongst these oxides, nanomaghemite has received special attention by virtue of its low price and low environmental impact [3,4,5,6]. Different studies have been done to investigate the electrochemical properties of maghemite. The effect of particle size on electrochemical properties of maghemite has not been explicitly studied. We have used Electrochemical Impedance Spectroscopy (EIS) and Diffuse Reflection Spectroscopy (DRS) investigations to understand the lithium insertion– deinsertion behavior
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