Chromium-ion doped spinel lithium manganate nanoparticles derived from the sol-gel process

Abstract

Lithium ion secondary batteries have been widely applied in high-tech electronic devices such as cellular phones and notebook computers owing to their high working voltage, low self-discharge rate, and elevated energy density [1, 2]. In lithium ion batteries, cathode materials play an important role in modulating the electrochemical performance. Lithiated transition oxides such as lithium cobalt oxide, lithium nickelate, and lithium manganate are usually adopted as the cathode materials. LiMn2O4 is a potential cathode material owing to its low cost, low toxicity, and acceptable safety [3–6]. However, LiMn2O4 suffers a severe capacity fading problem after long-term cycling, and such a problem limits its application. In order to improve the cycleability of LiMn2O4, doping other cations into the spinel compound has been intensively investigated [7–9]. The spinel compound can be stabilized via doping M (III) cations into the host structure by inhibiting the Jahn-Teller distortion. In the previous work, chromium ions have been found to be an effective dopant for improving the cycling performance of LiMn2O4 [10]. Traditionally, LiMn2−x Crx O4 powders are prepared through the solid-state reaction; however, the particle size of the obtained powders is large and their morphology is not well controlled. In order to obtain ultrafine and uniform cathode powders, some newly developed solution techniques have been been used to satisfy these demands [11–14]. A PVA sol-gel process has been investigated in this study. This process has been found to be a potential method to prepare nanosized ceramic powders with improved electrochemical performance. It is revealed that the obtained powders exhibit not only enhanced cycling performance, but also good discharge capacities at ambient temperature as well as elevated temperatures. An aqueous solution containing lithium nitrate (LiNO3), chromium nitrate (Cr(NO3)3), and manganese nitrate (Mn(NO3)2) was initially prepared with the overall cationic concentration maintained at 1 M. Reagent-grade PVA was completely dissolved in deionized water, and then added into the above solution. The resulting viscous solution comprising of the starting materials and the PVA solution was dried at 80 ◦C to obtain the precursor powders. These dried precursor powders were subsequently calcined at various temperatures ranging from 500 to 900 ◦C to synthesize the desired spinel compounds.