LiMg[sub x]Mn[sub 1−x]PO[sub 4]/C Cathodes for Lithium Batteries Prepared by a Combination of Spray Pyrolysis with Wet Ballmilling

Abstract

The LiMg x Mn 1−x PO 4 /C ͑x = 0, 0.02, 0.04, 0.12͒ composite cathode was successfully prepared by a combination of spray pyrolysis and wet ballmilling with heat-treatment. The composite cathode had narrow particle size distribution with an average particle size of 99 nm. The Mg doping on the Mn site led to the electrochemical performance enhancement of the composite cathode, which was confirmed by cyclic voltammetry, ac impedance spectroscopy, and charge-discharge tests. The Mg-doped composite cathode exhibited a high discharge capacity in lithium cell, which remarkably increased with an increase in the charge cutoff voltage under galvanostatic charge-discharge. The LiMg 0.04 Mn 0.96 PO 4 /C cathode exhibited a discharge capacity of 154 mAh g −1 ͑above 93% of the theoretical value͒ at 0.1C when charge-discharged galvanostatically to 4.9 V. Along with enhanced discharge capacity, the cell exhibited a good rate capability under the galvanostatic charge-discharge. Under the trickle mode conditions, the cell exhibited discharge capacities of 154, 136, 106, and 74 mAh g −1 at 0.05, 0.1, 1, and 5C, respectively. © 2010 The Electrochemical Society. ͓DOI: 10.1149/1.3294698͔ All rights reserved. Lithium-ion batteries ͑LIBs͒ are leading the rapidly growing market of portable power sources for various applications starting from the miniature devices, such as peacemakers and chipsets, to electricity powered automobiles and energy storage facilities. Rechargeable LIBs with liquid electrolytes were developed and introduced into the market by Sony Corporation 1 in 1991. Despite its outstanding properties compared with other types of batteries such as nickel-cadmium and metal hydride batteries, LIBs suffer from the application of high cost and toxic materials, mainly as positive electrodes. Therefore, the main demand in the field of LIBs is to develop low cost and environment-friendly materials to substitute commercial cathodes such as expensive and toxic cobalt-containing cathodes. Among other candidates to replace the high cost and toxic cobalt-based cathodes for LIBs, the olivine structured phosphates LiMPO 4 ͑M = Fe, Mn, Ni͒ are the most promising ones due to the reliable combination of theoretical capacity and cost, nontoxicity, and high electrochemical and thermal stabilities.2-5 However, high ionic and electronic resistance of these materials restricts achieving high electrochemical activity. This disadvantage has been successfully overcome for the LiFePO 4 cathodes via the synthesis of nanosized powders, the conductive layer coating of the compound particles surface and doping with cations. [3][4][5][6][7][8][9] It was shown that in the presence of carbon in the cation-doped olivine LiFePO 4 , the carbothermal reduction of iron phosphate at high temperatures leads to the formation of phosphides at the grain boundaries, and this nanonetwork could be responsible for the grain-boundary transport enhancement.9,10 The same process could be readily extendable to other olivines such as LiMnPO 4 .9 Chung et al. 11 showed tha...

Synthesis of Multiwalled Carbon Nanotube Aqueous Suspension with Surfactant Sodium Dodecylbenzene Sulfonate for Lithium/Sulfur Rechargeable Batteries

“…It can be seen that for both cathodes the Nyquist plots are presented by a semicircle in the high-to-medium frequency range, related to interfacial charge transfer impedance, followed by a declined line of the Warburg impedance in the low frequency part attributed to the bulk diffusion resistance of the composite cathode. 17,18 A much smaller highto-medium frequency semicircle can be seen in the S/MWNT composite electrode EIS spectra compared with that of the S/ MWNT mixture. These trends support our suggestion on the conducting property enhancement by addition of a homogeneouslydispersed MWNT suspension as precursor to prepare S/MWNT composite.…”

LiMnPO4 Olivine as a Cathode for Lithium Batteries

“…It was shown that the cation-doping of LiMnPO 4 by electrochemically nonactive metals seems to be more attractive than the mixed Mn-Fe compounds, because along with its electrochemical performance improvement this provides a constant voltage operation of the material based on a single redox reaction Mn 3+ /Mn 2+ [30]. It was shown that the most effective dopant for LiMnPO 4 is Mg [31].…”

“…This method produces fine spherical particles with homogeneous chemical composition in a short time [34,30]. In our systematic research on the preparation of cathode materials for lithium batteries using SP technique [32,33,[35][36][37], we have shown that various lithium metal oxides and phosphates nanoparticles could be successfully prepared by SP and these nanoparticles exhibited enhanced electrochemical performance.…”

“…The Mg-doped lithium manganese phosphate cathode materials of a general formulae LiMg x Mn 1 x PO 4 (x = 0, 0.02, 0.04, 0.12) were prepared by SP at 400 °C using a N 2 + 3% H 2 mixture as a carrying gas [30]. In order to increase the materials conductivity, the as-prepared samples were subjected to wet ballmilling (WBM) with acetylene black (AB) and heat-treated at 500 °C in a N 2 + 3% H 2 gas media for 4 h in a tubular furnace.…”

“…The composite particles had a narrow particles size distribution with a mean particle size around 100 nm. The composite cathodes were successfully cycled in a lithium cell under galvanostatic conditions [30]. The highest discharge capacity of 91 mAh g 1 was shown by the LiMg 0.04 Mn 0.96 PO 4 /C cathode when cycled to 4.4 V cutoff voltage.…”