Co-Doped Co[sub x]Cu[sub 6−x]Sn[sub 5] Alloys as Negative Electrode Materials for Rechargeable Lithium Batteries

Abstract

A series of Co-doped Co x Cu 6−x Sn 5 ͑0 ഛ x ഛ 2͒ alloys were prepared by mechanical alloying, followed by annealing at 400°C. The Co-doped alloys show the same structure as the Cu 6 Sn 5 , which can be indexed to a hexagonal NiAs-type cell, but differ in the electrochemical performance as the anodes of Li-ion batteries. The results of ex situ X-ray diffraction analysis indicate the different Li alloying mechanism among Co x Cu 6−x Sn 5 . The metastable intermediate phases of Li 2 Co y Cu 1−y Sn formed during the Li-ion insertion process of Co x Cu 6−x Sn 5 become unstable and even undetectable with increasing amounts of Co substituted. A proper amount of Co-doped alloy, CoCu 5 Sn 5 , showed improved cycling stability at the expense of capacity, whereas a heavy Co-doped alloy, Co 2 Cu 4 Sn 5 , resulted in poor cycling ability. The crystal and electronic structure, thermodynamic stability of Co x Cu 6−x Sn 5 and half-lithiated alloy, Li 2 Co y Cu 1−y Sn, as well as the average voltage of alloying reaction in terms of different discharge depths were investigated using first-principles density-functional theory with pseudopotentials and plane wave basis. Lithium-ion batteries based on a carbon/graphite anode and a transition metal-oxide cathode have been commercially used in popular portable devices such as cellular phones and laptop computers for about 15 years. One of the most interesting and challenging goals is to develop increased capacity electrode materials in order to increase the battery energy density. The conventional anode material, graphite, has a theoretical maximum capacity of 372 mAh/g, or a volumetric capacity of 818 Ah/L ͑the density of graphite is 2.2 g/cm 3 ͒. Metals and alloys present an attractive alternative to graphite as anode materials for lithium-ion batteries due to the high capacity, an acceptable rate capability, and operating potentials well above the potential of metallic lithium. In particular, the intermetallic compounds ͑MЈM͒ show the most promising possibilities.1-3 It typically consists of an "inactive phase MЈ," which does not react with lithium, and an "active phase M," which reacts with lithium.Introducing an inactive phase MЈ can reduce the volume expansion/ contraction to some extent, thus improving its cycling performance. According to the lithium-ion alloying mechanism, the alloys can be divided into two groups. The first one refers to those alloys in which the reaction of lithium results first in the formation of Li x MЈM as an intermediate phase, while further reaction leads to a mixed phase of the disordered Li x M alloy and metal MЈ, and the initial intermetallic alloys are reformed when lithium is extracted from the alloys during charge, such as Cu 6 Sn 5 , 1,4 InSb, 5,6 etc. The other group refers to those alloys in which the reaction of lithium in the MЈM results directly in the formation of a disordered Li x M alloy and metal MЈ matrix, but MЈ cannot recombine with M to reform the initial intermetallic compounds during the charge, such as Sn-Mn, 2 Sn-Fe, 3 and Co-...

Electrochemical kinetics study of Li-ion in Cu6Sn5 electrode of lithium batteries by PITT and EIS

“…Synthesis of Cu 6 Sn 5 was described elsewhere [25]. The compound was characterized by powder X-ray diffractometer (Bruker Advance8) with Cu Ka radiation.…”

“…However, few works in the study of lithium diffusion in alloys has been reported. In our previous work, we studied the Cu 6 Sn 5 and its Co and Ni substituted alloys as lithium batteries anodes [25,26], and the relationship between the structural properties and the electrochemical performance was discussed using the experiments as well as the first-principles calculations. Following the previous studies, the goal of this paper is to investigate the kinetics of the intercalation of lithium into the Cu 6 Sn 5 alloys using both PITT and EIS method.…”

Sn‐based Intermetallic Compounds for Li‐ion Batteries: Structures, Lithiation Mechanism, and Electrochemical Performances

“…Here, the Sn is also the main electrochemical active component for lithium storage . The third element (M′), such as Sb, Zn, Co,, and B could be both active and inactive for lithium storage. For example, the Sb is lithium‐active, which can alloy with lithium to form the Li 3 Sb in the alloying process, deriving a theoretical capacity of 660 mAh g −1 .…”

Synthesis and characterization of Sn–Mo mixtures as negative electrode materials for Li-ion batteries

“…It is due to displaying higher reversible specific capacities than carbon and the higher safety against the formation of lithium metal dendrites. Especially, tin-based metal alloys due to their low cost and high energy densities are the most exploited of alternative anode materials in lithium-ion batteries [10][11][12][13][14][15][16][17][18][19]. While tin metals can give high initial lithium insertion capacities, corresponding to a theoretical capacity of 990 mAh g −1 .…”