Thermodynamic investigations of copper oxides used as conversion type electrodes in lithium ion batteries

Copper oxides, which exhibit the conversion mechanism with lithium during electrochemical cycling, are promising electrode materials for next-generation lithium ion batteries. To better understand phase formations and equilibria in the Li–Cu–O system, the LiCu2O2 phase was synthesized using the solid-state method and characterized with X-ray powder diffraction technique and Rietveld analysis as well as inductively coupled plasma—optical emission spectrometry (ICP–OES). The phase stabilities in argon atmosphere and in a mixture of argon and oxygen were determined between 200 and 900 °C and between 200 and 950 °C, respectively. Based on this data as well as on other literature data, a thermodynamic description of the Li–Cu–O system valid in the battery relevant temperature regime was developed using the CALPHAD method. From this thermodynamic description, titration curves for CuO and Cu2O cathodes, which give the equilibrium cell voltage as a function of lithium content along a selected composition path, were calculated at different temperatures.