Oxygen Release Degradation in Li‐Ion Battery Cathode Materials: Mechanisms and Mitigating Approaches

Abstract

Widespread application of Li‐ion batteries (LIBs) in large‐scale transportation and grid storage systems requires highly stable and safe performance of the batteries in prolonged and diverse service conditions. Oxygen release from oxygen‐containing positive electrode materials is one of the major structural degradations resulting in rapid capacity/voltage fading of the battery and triggering the parasitic thermal runaway events. Herein, the authors summarize the recent progress in understanding the mechanisms of the oxygen release phenomena and correlative structural degradations observed in four major groups of cathode materials: layered, spinel, olivine, and Li‐rich cathodes. In addition, the engineering and materials design approaches that improve the structural integrity of the cathode materials and minimize the detrimental O2 evolution reaction are summarized. The authors believe that this review can guide researchers on developing mitigation strategies for the design of next‐generation oxygen‐containing cathode materials where the oxygen release is no longer a major degradation issue.

Unveiling Nickel Chemistry in Stabilizing High‐Voltage Cobalt‐Rich Cathodes for Lithium‐Ion Batteries

“…In O K-edge, the pre-edge corresponds to transition from O core 1s to the unoccupied hybridized band state of O 2p and TM 3d orbitals, indicating the hole states in TMO bonding. [41,46,47] Ni segregation helps in this regard, because the higher fraction of Ni on surface contributes to capacity without coupling to O 2p orbitals, due to the higher electronic energies of Ni 3+/4+ :e g compared to Co 3+/4+ :t 2g & O 2p resonant band. [13,45] Since the oxidation of O 2− (forming mobile peroxo O 1− ) results in serious side reactions due to oxygen loss and high chemical reactivity toward electrolyte, we believe less O 1− generation on surface must be beneficial.…”

“…[13,45] Since the oxidation of O 2− (forming mobile peroxo O 1− ) results in serious side reactions due to oxygen loss and high chemical reactivity toward electrolyte, we believe less O 1− generation on surface must be beneficial. [41,46,47] Ni segregation helps in this regard, because the higher fraction of Ni on surface contributes to capacity without coupling to O 2p orbitals, due to the higher electronic energies of Ni 3+/4+ :e g compared to Co 3+/4+ :t 2g & O 2p resonant band. [14] Consistently, there is less gas evolution for LCNO than LCO during first charge, as supported by in situ differential electrochemical mass spectrometry (DEMS) data in Figure 3k.…”

Surface/Interface Structure Degradation of Ni‐Rich Layered Oxide Cathodes toward Lithium‐Ion Batteries: Fundamental Mechanisms and Remedying Strategies

“…ii) The dissolution of TM ions and organic electrolyte decomposition starting from the electrode/electrolyte interface are engendered by the highly oxidized Ni 4+ ions during charge–discharge process, which is highly intensified due to the emergence of microcracks resulting from the anisotropic contraction and expansion . iii) The overcharged cathodes are susceptible to thermal decomposition, thus breaking down the TM‐O bonds and releasing oxygen from the host lattice . These detrimental cases preferentially take place at the surface/interface of highly delithiated electrodes.…”

Monitoring the phase evolution in LiCoO2 electrodes during battery cycles using in‐situ neutron diffraction technique

“…The SEM images clearly show increased cracking of the LCO‐A relative to the LCO‐B electrode. Such damage results in the deterioration of the LCO electrode and is commonly associated with O 2 release during high‐voltage charging from cleaving of the Co‐O bond . This is facilitated by the exposure to HF formed from electrolyte decomposition at higher voltages, where more of the LCO‐A active material is exposed due to its higher surface area …”