In the search for new materials that can react and host large amounts of lithium-ions, tin has attracted a large interest. Tin can alloy with lithium with a total amount of 4 lithium per atom. Electrochemically this is occurring at low potentials vs. Li/Li⁺, which makes tin interesting as an anode material for Li-ion batteries. A number of different phases are formed when lithium is alloying with tin. This electrochemical process can be followed by in situ powder X-ray diffraction, which today is a standard technique within the field of lithium battery research. During the lithiation process the volume of the tin particles are expanding up to 358% for the fully lithiated sample. This imposes large strains in the composite electrode matrix leading to cell failure due to crack formation of the electrode and loss of particle contact. There are different ways to circumvent this problem and we have earlier shown that forming intermetallic compound of tin with copper (that do not react with lithium) can decrease the strain in the material [1]. We showed for Cu₆Sn₅ that lithium reacts with the formation of an intermediate phase, Li₂CuSn, while copper is being extruded from the structure and that at a potential below 0.2V vs. Li/Li⁺, Li ₄Sn is formed. During extraction of the lithium ions the copper is entering the structure and Cu₆Sn₅ could be reformed.

In this study we have used a pulsed electrochemical method to study the structural kinetic response to lithium insertion in a number of Cu₆Sn₅ analogs where one of the copper atoms has been replaced with another metal: CoCu₅Sn₅; ZnCu₅Sn₅; FeCu₅Sn₅; and MnCu₅Sn₅. We show how the lithium insertion properties are influenced both electrochemically and structurally by the use of time-resolved X-ray diffraction data produced at the Swedish synchrotron MAXlab in Lund. The diffraction set-up is simple as shown in Fig. 1 and the battery is made of a polymer laminated aluminium pouch. This battery type is as similar to those used in commercial systems as possible.

Fig. 1. A battery cell connected to a potentiostat at the 711 beam-line, MAXlab, Sweden.

References

[1] L. Fransson, E. Nordström, K. Edström, L. Häggström, J.T. Vaughey and M.M. Thackeray. J. Electrochem. Soc. 149 (2002) A736.

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1. In situ neutron diffraction from Li-ion batteries