Synthesis, Structure, and Electrochemical Performance of High Capacity Li₂Cu_0.5Ni_0.5O₂ Cathodes

Abstract

and solid solutions thereof have been studied as potential cathode materials for lithium-ion batteries due to their high theoretical capacity and relatively low cost. While neither endmember shows good cycling stability, the intermediate composition, Li 2 Cu 0.5 Ni 0.5 O 2 , yields reasonably high reversible capacities. A new synthetic approach and detailed characterization of this phase and the parent Li 2 CuO 2 are presented. The cycle life of Li 2 Cu 0.5 Ni 0.5 O 2 is shown to depend critically on the voltage window. The formation of Cu 1+ at low voltage and oxygen evolution at high voltage limit the electrochemical reversibility. In situ X-ray absorption spectroscopy (XAS), in situ Raman spectroscopy, and gas evolution measurements are used to follow the chemical and structural changes that occur as a function of cell voltage.

Investigating Li2NiO2–Li2CuO2 Solid Solutions as High-Capacity Cathode Materials for Li-Ion Batteries

“…Our data interpretation focuses on the shape of the spectral fine features to guide our analysis on the oxidation state and coordination environment of Cu during the electrochemical reaction. As shown in Figure 5b, the K-edge XANES of Cu in the pristine Li 2 Ni 0.8 Cu 0.2 O 2 exhibited two rising-edge transitions centered around 8984 and 8990 eV, which was in agreement with those of previous reported spectra, 21 corresponding to the electric dipole transitions from the 1s state to various np final states. 40 When charged to 3.8 V, the two rising edges around 8984, and 8990 eV almost vanished and ended at a more smooth main edge.…”

“…Such dramatic change in the Cu K-edge XANES, after charging Li 2 Ni 0.8 Cu 0.2 O 2 to 3.8 V, was in agreement with those previously reported by Ruther et al and could be ascribed to the retained Cu 2+ . 21 According to the previous electrochemical study on Li 2 CuO 2 , 27 oxidation of Cu from 2+ to 3+ was possible upon lithium removal. In our case, we did not observe a clear shift in Cu energy edge to support the formation of Cu 3+ at 3.8 V charge.…”

“…14 18 Recently, Ruther et al performed a comprehensive study on the electrochemical reaction mechanism of Li 2 Cu 0.5 Ni 0.5 O 2 using a suite of characterization techniques, revealing a reversible Ni 2+ / Ni 3+ redox reaction coupled with O 2 evolution at a high charge voltage (>3.9 V) and Cu 2+ to Cu + reduction at a low discharge voltage (<1.8 V). 21 Oxygen oxidation was also proposed and gas evolution was detected by other groups, 25,31 but no quantification work has been performed to isolate the evolved gas species and correlate the oxygen redox with electrochemistry.…”

“…42,43 Beginning at ∼4.0 V, there was a burst of O 2 evolution not explained by electrolyte oxidation, suggesting that lattice oxygen ions were directly involved in the redox reaction. 9,21 The gas evolution measurement provides useful insights into the understanding of anionic oxygen redox during charge, especially in the high voltage region. As discussed above, Ni oxidation was the dominant process up to 3.8 V, followed by almost no detectable change in the oxidation state of Cu and Ni.…”

Studies on the local structures for the trigonal Ni3+ centers in cathode materials LiAlyCo1–yO2 (y = 0, 0.1, 0.5, and 0.8)

“…LiCoO 2 containing other cations such as aluminum and nickel has attracted intense interest of authors because of wide applications in lithium‐ion batteries . Recently, the layered cathode materials of battery based on the different concentrations of these ions in LiCoO 2 have been extensively studied, for example, low‐spin Ni 3+ in LiM y Co 1–y O 2 (M = Al, Ga) .…”