Transport properties and lithium insertion study in the p-type semi-conductors AgCuO2 and AgCu0.5Mn0.5O2

The transport properties and lithium insertion mechanism into the first mixed valence silver–copper oxide AgCuO2 and the B-site mixed magnetic delafossite AgCu0.5Mn0.5O2 were investigated by means of four probes DC measurements combined with thermopower measurements and in situ XRD investigations. AgCuO2 and AgCu0.5Mn0.5O2 display p-type conductivity with Seebeck coefficient of Q=+2.46 and +78.83 μV/K and conductivity values of σ=3.2×10−1 and 1.8×10−4 S/cm, respectively. The high conductivity together with the low Seebeck coefficient of AgCuO2 is explained as a result of the mixed valence state between Ag and Cu sites. The electrochemically assisted lithium insertion into AgCuO2 shows a solid solution domain between x=0 and 0.8Li+ followed by a plateau nearby 1.7 V (vs. Li+/Li) entailing the reduction of silver to silver metal accordingly to a displacement reaction. During the solid solution, a rapid structure amorphization was observed. The delafossite AgCu0.5Mn0.5O2 also exhibits Li+/Ag+ displacement reaction in a comparable potential range than AgCuO2; however, with a prior narrow solid solution domain and a less rapid amorphization process. AgCuO2 and AgCu0.5Mn0.5O2 provide a discharge gravimetric capacity of 265 and 230 mA h/g above 1.5 V (vs. Li+/Li), respectively, with no evidence of a new defined phases.

Investigation on the transport properties of AgCuO2 and the new B-site mixed Delafossite AgCu0.5Mn0.5O2 shows a p-type conductivity of σ=3.2×10−1 and 1.8×10−4 S/cm, respectively. The high conductivity, as a result from a high charge carrier density in AgCuO2 supports the existence of a mixed valence state between silver and copper. A particular emphasis is also placed on the electrochemical lithium insertion properties into these two materials by in situ XRD measurements to better insight on the Li+ insertion mechanism and also scrutinize possible new compounds electrochemically accessible in the Li–Ag–Cu system.Figure optionsDownload as PowerPoint slide