Abstract
Recent studies of lithium-ion batteries suggest that the use of binary CoSn alloys as anodes should provide an improvement over currently used anode materials. However, the implementation of CoSn alloys is challenging due to uncertainties regarding the phase transformations within this system. In order to understand these, we evaluate the compositions of different intermetallic compounds produced via the peritectic reactions, nucleate and grow within the microstructure of binary Sn − 25 at.% Co by employing atom probe tomography (APT). The stoichiometric phase, which is produced upon the cooling of the melt, is not only found as part of the peritectic solidification sequence but also as clusters within the pure Sn phase. The phase was found as a nano sized layer and is attributed to the peritectic reaction between the phase and the pure Sn phase. The production of the compound was enhanced by the phase transformation of the phase. Furthermore, clusters had formed in the pure Sn phase. A limited solubility within the pure Sn phase was also determined to be (0.6 ± 0.1) at.% Co.
Highlights
In comparison to currently used anodes in lithium ion batteries, especially carbonaceous materials, intermetallics promise higher energy densities in combination with relatively safe lithiation and delithiation voltages
In order to understand these, we evaluate the compositions of different intermetallic compounds produced via the peritectic reactions, nucleate and grow within the microstructure of binary Sn − 25 at.% Co by employing atom probe tomography (APT)
The objective of this study is to investigate the peritectic reactions within the binary Co–Sn alloy to understand the phase transformation between different intermetallic phases which are; CoSn, CoSn2, CoSn3, and pure Sn phase at atomic scale
Summary
In comparison to currently used anodes in lithium ion batteries, especially carbonaceous materials, intermetallics promise higher energy densities in combination with relatively safe lithiation and delithiation voltages. Sn-based alloys have been used in many different applications such as solder bumps [1], joining materials [2], and galvanizing technologies [3] Their most attractive application related to lithium ion batteries would be as electrodes [4,5,6], due to the 2.5 times higher theoretical capacity of batteries with Sn electrodes in comparison to graphite (372 mAh g−1 for graphite and 994 mAh g−1 for Sn) [7]. The Co–Sn system has recently drawn increasing attention due to its special features such as amorphous Co–Sn particles, obtained by electrodeposition on a rough Cu foil [13], and nano CoSn crystals with different crystallite size [12] These features improve the electrochemical behaviour of the CoSn material and that make it an attractive alternative for different industrial applications
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