Oxygen Anion Redox Chemistry Correlated with Spin State in Ni‐Rich Layered Cathodes

Abstract

Despite the low cost and high capacity of Ni‐rich layered oxides (NRLOs), their widespread implementation in electric vehicles is hindered by capacity decay and O release. These issues originate from chemo‐mechanical heterogeneity, which is mainly related to oxygen anion redox (OAR). However, what to tune regarding OAR in NRLOs and how to tune it remains unknown. In this study, a close correlation between the OAR chemistry and Li/Ni antisite defects is revealed. Experiments and calculations show the opposite effects of aggregative and dispersive Li/Ni antisite defects on the NiO6 configuration and Ni spin state in NRLOs. The resulting broad or narrow spans for the energy bands caused by spin states lead to different OAR chemistries. By tuning the Li/Ni antisite defects to be dispersive rather than aggregative, the threshold voltage for triggering OAR is obviously elevated, and the generation of bulk‐O2‐like species and O2 release at phase transition nodes is fundamentally restrained. The OAR is regulated from irreversible to reversible, fundamentally addressing structural degradation and heterogeneity. This study reveals the interaction of the Li/Ni antisite defect/OAR chemistry/chemo‐mechanical heterogeneity and presents some insights into the design of high‐performance NRLO cathodes.

Mitigating voltage decay of O3‐NaNi1/3Fe1/3Mn1/3O2 layered oxide cathode for sodium‐ion batteries by incorporation of 5d metal tantalum

“…Moreover, when the potential is above 4.0 V, irreversible redox reactions of oxygen ions tend to occur, which can negatively impact cycling performance. [49] The introduction of strong TM-O bonds through Ta doping helps stabilize the structure and improve cycling performance, making them promising materials for battery applications. Furthermore, the dQ/dV curves in Figure 4b also show a peak around 3.0 V, representing the O3-P3 phase transition.…”

Li/Ni Intermixing: The Real Origin of Lattice Oxygen Stability in Co‐Free Ni‐Rich Cathode Materials

“…In addition, the Ni e g (split by d-orbit) and O 2p energy band span of NM90-Mixing was elongated (see the blue arrow), and its O 2p orbital take a jump toward lower energy levels; this can be explained as the Li/Ni intermixing increasing the spin state of Ni and then complicating the electronic structure. [29,50] Therefore, the band structure of NM90-Mixing can reduce the overlapping between the Ni e g and O 2p bands near the Fermi level, which consequently reduces the charge compensation and thus effectively suppresses the oxygen release, [30] also as shown in the schematic (Figure 4j,k). In summary, the Li/Ni intermixing configuration can increase oxygen vacancy formation energy and reduce charge compensation, which leads to a significant enhancement of the lattice oxygen stability of Co-free Ni-rich cathodes.…”

Low‐Electronegativity Cationic High‐Entropy Doping to Trigger Stable Anion Redox Activity for High‐Ni Co‐Free Layered Cathodes in Li‐Ion Batteries

“…The peaks at 526 eV and 532 eV are assigned to O 2À and (O 2 ) nÀ , and the corresponding peak intensity ratio of I(O 2 ) nÀ /IO 2À reflects the variation of the O 2À and (O 2 ) nÀ content. [18,43] Figure 6g and Figure 6h are the comparisons of XPS and XANES results for various cationic high-entropy-doped cathodes and NCM-811, which show that the (O 2 ) nÀ content of high-entropy-doped cathodes (HE-WD and HE-comparison) is much higher than that of NCM-811, indicating the reversible O 2À ) *(O 2 ) nÀ is effectively promoted and extra capacity provided by anion redox activity is achieved. Since the configurational disorder [60] originated from cationic highentropy doping in TM layer can suppress the TM rearrangement and the collapse of anionic framework.…”

“…So it comes to the capacity provided by anionic charge compensation. [17][18][19][20] Recent works on Ru [21][22][23][24] (or Mn, [25][26][27][28] or Ir [29][30][31] )-based cathodes give a hint that oxygen redox activity holds the promise of exceeding the limits of high-Ni cathodes to realize higher capacity through the charge compensation on lattice oxygen (O 2À ). However, oxygen redox in TM layer is always accompanied by the anionic redox irreversibility and structure instability, leading to the formation of O 2 .…”