Extended Interfacial Stability through Simple Acid Rinsing in a Li-Rich Oxide Cathode Material

Abstract

Layered Li-rich Ni, Mn, Co (NMC) oxide cathodes in Li-ion batteries provide high specific capacities (>250 mAh/g) via O-redox at high voltages. However, associated high-voltage interfacial degradation processes require strategies for effective electrode surface passivation. Here, we show that an acidic surface treatment of a Li-rich NMC layered oxide cathode material leads to a substantial suppression of CO 2 and O 2 evolution, 90% and ~100% respectively, during the first charge up to 4.8 V vs. Li +/0. CO 2 suppression is related to Li 2 CO 3 removal as well as effective surface passivation against electrolyte degradation. This treatment does not result in any loss of discharge capacity and provides superior long-term cycling and rate performance compared to as-received, untreated materials. We also quantify the extent of lattice oxygen participation in charge compensation ("O-redox") during Li + removal by a novel ex-situ acid titration. Our results indicate that the peroxo-like species resulting from O-redox originate on the surface at least 300 mV earlier than the activation plateau region around 4.5 V. X-ray photoelectron spectra and Mn-L X-ray absorption spectra of the cathode powders reveal a Li + deficiency and a partial reduction of Mn ions on the surface of the acid-treated material. More interestingly, although the irreversible oxygen evolution is greatly suppressed through the surface treatment, our O K-edge resonant inelastic X-ray scattering shows the lattice O-redox behavior largely sustained. The acidic treatment, therefore, only optimizes the surface of the Li-rich material and almost eliminates the irreversible gas evolution, leading to improved cycling and rate performance. This work therefore presents a simple yet effective approach to passivate cathode surfaces against interfacial instabilities during high-voltage battery operation. File list (2) download file view on ChemRxiv McCloskey_manuscript.pdf (2.13 MiB) download file view on ChemRxiv McCloskey_SuppInfo.pdf (5.91 MiB)

Anion Reactivity in Cation‐Disordered Rocksalt Cathode Materials: The Influence of Fluorine Substitution

“…The tendency for the majority of the peroxo‐like oxygen to return to oxide suggests that first cycle oxygen redox is mostly reversible in DRX materials, and certainly more reversible than oxygen redox in Li/Mn rich layered oxides. [ 34 ] Looking next at the fourth cycle titrations, similar conclusions can be drawn about the reversibility of oxygen redox on subsequent cycles. After the fourth charge, the amount of peroxo‐like oxygen present is similar to the amount after first charge.…”

“…At the same time, electrolyte solvent oxidation and solid carbonate oxidation lead to the deposition and removal of solid carbonates from the surface of DRX materials, respectively. [ 33,34 ] Studying the formation of these species provides information about the delithiation charge compensation mechanism and active electrochemistry occurring at high voltages. To measure the amount of peroxo‐like oxygen species and surface carbonates produced during the first charge, LMNO and LMNOF cathodes were extracted at different cutoff voltages for acid titration using TiMS.…”

Phosphoric acid and thermal treatments reveal the peculiar role of surface oxygen anions in lithium and manganese-rich layered oxides

“…$4.5 V Li + /Li ). [8][9][10] Among these compounds, Li-and Mn-rich layered oxides (LMLOs) are at the forefront of this area achieving high discharge capacities above 250 mA h g À1 . 11,12 However, the oxygen redox activity always causes changes in the crystallographic structure, surface inhomogeneity and release of lattice oxygen in LMLOs, thereby resulting in structural instability and severe voltage fading.…”

“…For example, Ramakrishnan et al achieved an extended interfacial stability of Li-rich oxide cathodes on the surface through a strong H 2 SO 4 acid rinsing, which could suppress the irreversible oxygen evolution and improve the cycling and rate performance. 8 Wu et al tuned the oxygen redox reaction through the inductive effect with proton insertion in Li-rich oxides, thus stabilizing the oxygen activity during charging. 30 Paik et al studied the acid leaching of the layered compound Li 2 MnO 3 , showing an H + /Li + ion exchange with a shearing of the oxygen layers driven by hydrogen bonding, observed by 6 Li and 2 H MAS NMR measurements in conjunction with X-ray diffraction.…”

Rational Design of a Piezoelectric BaTiO3 Nanodot Surface‐Modified LiNi0.6Co0.2Mn0.2O2 Cathode Material for High‐Rate Lithium‐Ion Batteries

“…To evaluate the inhibition effect of the modification process on the surface residual contaminations and the stability of electrochemical cycling of 0.5 %-NCM622@BTO. [47,48] The differential electrochemical mass spectrometer (DEMS) was performed to monitor the cycling performance of the pristine NCM622 and 0.5 %-NCM622@BTO at 0.1 C with the potential range of 3.0-4.5 V and the possible by-product CO 2 generated by the battery system was quantitatively analyzed in real-time. For pristine NCM622, it can be observed in Figure 7 that a relatively obvious peak of CO 2 gas is generated during the initial cycle, which is attribute to the decomposition of Li 2 CO 3 .…”