Abstract
A new route for the preparation of nickel and cobalt substituted spinel cathode materials (LiMn1.95Co0.025Ni0.025O4 and Li1.1Mn1.95Co0.025Ni0.025O4) by freeze-drying of acetate precursors followed by heat treatment was suggested in the present work. The experimental conditions for the preparation single-phase material with small particle size were optimized. Single-phase spinel was formed by low-temperature annealing at 700 °C. For discharge rate 0.2 C, the reversible capacities 109 and 112 mAh g−1 were obtained for LiMn1.95Co0.025Ni0.025O4 and Li1.1Mn1.95Co0.025Ni0.025O4, respectively. A good cycle performance and capacity retention about 90% after 30 cycles at discharge rate 0.2–4 C were observed for the materials cycled from 3 to 4.6 V vs. Li/Li+. Under the same conditions pure LiMn2O4 cathode materials represent a reversible capacity 94 mAh g−1 and a capacity retention about 80%. Two independent experimental techniques (cyclic voltammetry at different scan rates and electrochemical impedance spectroscopy) were used in order to investigate the diffusion kinetics of lithium. This study shows that the partial substitution of Mn in LiMn2O4 with small amounts of Ni and Co allows the cyclability and the performance of LiMn2O4-based cathode materials to be improved.
Highlights
In spite of emerging power sources, Li-ion batteries still remain the most attractive ones, since their first commercial application in 1991
The aqueous solutions of the following salts were used for the preparation of freeze dried precursors: Ni(CH3 COO)2 ·4H2 O, Co(CH3 COO)2 ·4H2 O, Mn(CH3 COO)2 ·4H2 O (Reachim, analytical grade), lithium acetate solution was prepared by dissolving Li2 CO3 (Reachim, analytical grade) in the acetic acid
TG (Thermogravimetry) curve of freeze dried (FD) precursor obtained from the solution containing Li, Mn, Ni
Summary
In spite of emerging power sources, Li-ion batteries still remain the most attractive ones, since their first commercial application in 1991. LiMn2 O4 spinel was firstly proposed as cathode materials by Thackeray in 1983 [2] and commercialized in 1996 [3,4]. It remains one of the promising cathode materials due to its high discharge potential (4 V vs Li/Li+ ), high safety, low cost and toxicity compared to LiCoO2 and. One of the substantial drawbacks of these materials is the increase in Mn3+ ions content during lithium intercalation at low potentials (~3 V). These ions cause a significant variation of unit cell volume due to Jahn-Teller effect which leads to break the interparticle contacts [6]
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