Surface/Chemically Modified LiMn[sub 2]O[sub 4] Cathodes for Lithium-Ion Batteries

Abstract

LiMn 2 O 4 spinel oxide has been surface/chemically modified with Li x CoO 2 , LiNi 0.5 Co 0.5 O 2 , Al 2 O 3 , and MgO using a chemical processing procedure followed by heat-treatment at 300-800°C. The surface/chemically modified samples show much better capacity retention at both 25 and 60°C than does the unmodified LiMn 2 O 4 ͑41% fade in 100 cycles at 60°C͒. Among the various compositions investigated, the LiNi 0.5 Co 0.5 O 2 -modified sample shows superior capacity retention with only 2.8% fade in 100 cycles at 60°C with around 110 mAh/g. The Al 2 O 3 -modified sample shows a higher capacity of 130 mAh/g, but with a faster fade ͑16% in 100 cycles at 60°C͒. The Li 0.75 CoO 2 -modified sample shows the best combination of capacity ͑124 mAh/g͒ and retention ͑8% fade in 100 cycles at 60°C͒. The modified samples also exhibit better capacity retention after aging at 55°C at 60-70% depth of discharge. is found to show excellent capacity retention with a capacity fade of Ͻ0.03% per cycle over 100 cycles at 60°C and C/2 rate. ExperimentalThe surface/chemical modification was accomplished by treating a commercially available LiMn 2 O 4 powder ͑Carus Chemical Company͒ with various amounts of the precursor solutions of Li x CoO 2 , LiCo 0.5 Ni 0.5 O 2 , Al 2 O 3 , or MgO through a chemical process so that the amount of the modifying material in the final product is 3-5 wt %.The modification with Li x CoO 2 and LiCo 0.5 Ni 0.5 O 2 involved a dissolution of the carbonates or acetates of the precursor metal ions in glacial acetic acid, refluxion of the mixture for about an hour, dispersion of the LiMn 2 O 4 spinel oxide in the precursor solution, evaporation of the solvent, and decomposition of the resultant product at around 400°C, followed by firing at 850°C in a flowing oxygen atmosphere for 12 h.The modifications with Al 2 O 3 and MgO involved the dispersion of the LiMn 2 O 4 spinel oxide in an aqueous solution of aluminum or magnesium nitrate, precipitation of hydrous aluminum or magnesium oxide over LiMn 2 O 4 particles through the addition of ammonium hydroxide, and heating the resultant product at 300 and 600°C, respectively, in air for 4 h.Cathodes were fabricated with the surface/chemically modified and unmodified LiMn 2 O 4 powder, Denka black carbon, and polytetrafluoroethylene ͑PTFE͒ binder in a weight ratio of 75:20:5. The electrochemical performances were evaluated with CR2032 coin cells assembled with the cathodes thus fabricated, metallic lithium anodes, polyethylene separators, and 1 M LiPF 6 in ethylene carbonate ͑EC͒ and diethyl carbonate ͑DEC͒ electrolyte between 3.5 and 4.3 V. Aging experiments were carried out as follows. After the first two cycles at a current density of 0.5 mA/cm 2 ͑C/2 rate͒, the coin cells were discharged to DOD ͑depth of discharge͒ values of 60 and 70% in the third cycle at room temperature. The cells were then subjected to aging at a constant temperature of 55°C for 100 h and the remaining capacity was determined by discharging the aged cells at room temperature to a cutoff vo...

Aluminum Borate Coating on High-Voltage Cathodes for Li-Ion Batteries

“…TEM observations of the AlPO 4 -coated LLNMC material prepared using this in situ method confirmed the superiority of this procedure in its ability to apply a thin, even layer of AlPO 4 to the surface of the cathode particles ( Figure S2), consistent with reports of other materials synthesized in this manner. 14,18,27,28 This procedure was used for both coated materials to keep their treatments as consistent as possible, even though the borate coating does not precipitate at the initial concentration.…”

TiO2 coating of LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion batteries

“…Choi [5] reported that LiNi 1/3 Co 1/3 Mn 1/3 O 2 gave a capacity of about 184 mAh g −1 over 2.5-4.6 V. However, its capacity fading became faster than that over 2.5-4.4 V. Surface coating was proven to be an effective method to reduce the electrolyte decomposition on the surface of the cathode materials. Experiments such as surface coating of LiMn 2 O 4 with MgO [6], Al 2 O 3 [6], SiO 2 [7], and LiCoO 2 [6,8,9] and surface coating of 5-V materials LiNi 0.5 Mn 1.5 O 4 with ZnO [10] were reported to improve markedly the capacity retention at elevated temperatures. Studies on the surface modifying of LiCoO 2 [11], LiNiO 2 [12], and LiNi 0.8 Co 0.2 O 2 [13,14] were also reported.…”

A review of recent developments in the surface modification of LiMn2O4 as cathode material of power lithium-ion battery

“…The reason for the improved elevated temperature properties of LMO coated by other electrode materials is that the surface coating reduces the dissolution of Mn, which results from the suppression of the electrolyte decomposition. The coated electrode materials include LiCoO 2 performed by sol-gel methods [32][33][34] [39], and LiCu x Mn 2−x O 4 [40]. The synthesis methods and the electrochemical performance of coating by other electrode materials are plotted in Table 2.…”