Elucidating anionic oxygen activity in lithium-rich layered oxides

Abstract

Recent research has explored combining conventional transition-metal redox with anionic lattice oxygen redox as a new and exciting direction to search for high-capacity lithium-ion cathodes. Here, we probe the poorly understood electrochemical activity of anionic oxygen from a material perspective by elucidating the effect of the transition metal on oxygen redox activity. We study two lithium-rich layered oxides, specifically lithium nickel metal oxides where metal is either manganese or ruthenium, which possess a similar structure and discharge characteristics, but exhibit distinctly different charge profiles. By combining X-ray spectroscopy with operando differential electrochemical mass spectrometry, we reveal completely different oxygen redox activity in each material, likely resulting from the different interaction between the lattice oxygen and transition metals. This work provides additional insights into the complex mechanism of oxygen redox and development of advanced high-capacity lithium-ion cathodes.

Composite‐Structure Material Design for High‐Energy Lithium Storage

“…This similar phenomenon also has been observed by O K‐edge XAS spectra, which proves the formation of peroxide and superoxide species . Furthermore, there is a direct evidence of the oxygen state change (oxygen redox) using resonant inelastic X‐ray scattering (RIXS) technique, during the charge/discharge process of Li 1.2 Ni 0.2 Mn 0.6 O 2 materials (Figure d) . When the Li 1.2 Ni 0.2 Mn 0.6 O 2 materials are charged to 4.8 V, an obvious RIXS feature appears (marked by white arrow in Figure d) at excitation and emission energies of 530.8 and 523.75 eV, respectively.…”

“…When the Li 1.2 Ni 0.2 Mn 0.6 O 2 materials are charged to 4.8 V, an obvious RIXS feature appears (marked by white arrow in Figure d) at excitation and emission energies of 530.8 and 523.75 eV, respectively. More importantly, this sharp RIXS feature disappears when discharged to 2.0 V, indicating that this feature is a characterized fingerprint of the oxygen state change during electrochemical cycling . Nevertheless, oxygen redox reaction has been demonstrated by researchers, another question has been put forward in determining whether the entire process is solely O 2− /O − or O 2− /O 2 redox, or a combination of both.…”

“…The while arrow points that striking RIXS feature appears. Reproduced with permission . Copyright 2018, Nature Publishing Group.…”

Surface Degradation and Chemical Electrolyte Oxidation Induced by the Oxygen Released from Layered Oxide Cathodes in Li−Ion Batteries

“…According to XAS in bulk sensitive mode, a feature at 530.8 eV related to the oxygen redox couple O 2− /O n− should increase, as a result of the oxygen oxidation along the second plateau ,,. The apparent absence of changes of the “O‐redox” component suggests that the oxidized oxygen is unstable at the surface and either reacts immediately with the electrolyte or is released, as O 2 gas, leaving reduced TMs on the cathode surface.…”

“…Region 3 (above 4.7 V, after oxygen gas detection) : Extending the potential further up to 4.8 V and 5.1 V, located in Region 3, strong O 2 and CO 2 gas release are detected on Li‐rich NCM on the basis of DEMS measurements ,,,,,. In this region, no significant changes are observed for both the O K‐edge and the TMs L‐edges (Figure ) as compared to the potential at 4.57 V. Despite the considerable amount of oxygen released, the surface of Li‐rich NCM remains covered with a partially oxidized Co and Ni and reduced Mn, Co and Ni.…”