Influence of Boron Substitution on the Crystal and Electronic Properties of LiCrO 2 Battery Cathode
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INTRODUCTION
MOBILE technologies have a high demand in the world with an immense impact on trade. Thus, nowadays, scientific studies mostly focused on the mobile energy supplies with higher capacity than the one in use. Among these studies, lithium-ion batteries have attracted considerable attention because of their applications in the vast areas, like computer, cell phone, and electrical vehicles.[1] Thus, researchers spent most of their effort on generating better lithium-ion batteries with higher performance but lower cost. A lithium-ion battery consists of three parts: a cathode, an anode, and an electrolyte. Cathodes of the batteries are the main playground in batteries due to intercalation properties in narrow range of materials. In the last decade, layered cathode materials have been attracting attention due to possibility to improve its electrochemical properties. Among these materials, LiCrO2 is one of the studied members of the layered cathode materials group with trigonal rhombohedral geometry and a space group of ‘‘R3m’’ with the lattice parameters a = 2.898 A˚, c = 14.423 A˚.[2–4] Despite the weak cathode properties, popularity of the Cr-based cathode materials comes
OSMAN MURAT OZKENDIR is with the Department of Nanotechnology and Advanced Materials, Institute of Natural Science, Mersin University, 33343 Mersin, Turkey, and also with the Energy Systems Engineering, Faculty of Technology, Mersin University, 33400 Tarsus, Turkey. Contact e-mail: [email protected] SULE ATES and GULTEKIN CELIK are with the Physics Department, Faculty of Science, Selcuk University, 42030 Selcuklu, Konya, Turkey. WANTANA KLYSUBUN is with the Synchrotron Light Research Institute (SLRI), 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand. Manuscript submitted October 23, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
from the electron transfer during an electrochemical reactions (Cr3+ to Cr6+).[4] As a member of this group, Li2MnO3-LiCrO2 attracted much interest with its stable cycle ability and high capacity.[5] Li2MnO3 material has been intensively studied as a cathode with Ni- and Co-doped products. However, due to oxygen loss causing an irreversible capacity loss, this material lost its popularity.[6–8] LiCrO2 is reported to show poor electrochemical properties as a cathode material, where Cr6+ is mainly responsible for the ‘‘freeze effects’’ both in electronic configuration and location. It was reported by Feng et al. that poor electrochemical cycling performances in the LiCrO2 cathode depend on the particle size in the material,[4] and when LiCrO2 powders have extremely small domain sizes, they could show enhanced reactivity. They proved the fact in a study by comparing the performances for different grain sizes and concluded that LiCrO2 powder materials with smaller grain size (50 nm).[9] In this study, influences of boron substitution on the crystal and electronic properties of cathode material LiCrO2 are studied by X-ray-based techniques: X-ray powder diffraction (XRD) and X-ray absorption fine str
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