Investigation of Nano-Sized Cu(II)O As a High Capacity Conversion Material for Li Metal Cells and Lithium Ion Full Cells

Qian Y, Niehoff P, Zhou D, Adam R, Mikhailova D, Pyschik M, Boerner M, Kloepsch R, Rafaja D, Schumacher G, Ehrenberg H, Winter M, Schappacher F

Abstract

In this study, nanostructured CuO electrodes are prepared, which show no capacity decay for 40 cycles at 0.1C in a half cell against Li metal. The reaction mechanisms of the CuO electrodes are investigated as the main focus. With the help of in situ EIS, in situ XRD, TEM, XAS, SQUID, IC and GC-MS, it is found that the as-prepared CuO electrode undergoes significant phase and composition changes during the initial lithiation, with the transformation of CuO to nano- crystalline Cu at the end of lithiation. During the 1st delithiation, Cu is inhomogeneously oxidized, which yields a mixture of Cu2O, Cu2-xO and Cu. The incomplete conversion reaction during the 1st cycle is attended by the formation and partial decomposition of the SEI as the side reactions. Nevertheless, from the 1st to 5th delithiation, the oxidation state of Cu approaches +2. After an additional formation step, the transformation to Cu and back to Cu2-xO keeps stable during the subsequent long-term cycling with no electrolyte decomposition products detected. The LiNi1/3Mn1/3Co1/3O2(NMC-111)/CuO full cells show high capacities (655.8 ± 0.6, 618.6 ± 0.9 and 290 ± 2 mAh/g at 0.1, 1 and 10C, respectively), within the voltage range of 0.7-4.0V at 20°C and a high capacity retention (85% after 200 cycles at 1C).