Understanding the Effects of Tetrahedral Site Occupancy by the Zn Dopant in Li-NMCs toward High-Voltage Compositional–Structural–Mechanical Stability via Operando and 3D Atom Probe Tomography Studies

Abstract

Ni-containing “layered”/cation-ordered LiTMO2s (TM = transition metal) suffer from Ni-migration to the Li-layer at the unit cell level, concomitant transformation to a spinel/rock salt structure, hindrance toward Li-transport, and, thus, fading in Li-storage capacity during electrochemical cycling (i.e., repeated delithiation/lithiation), especially upon deep delithiation (i.e., going to high states-of-charge). Against this backdrop, our previously reported work [ACS Appl. Mater. Interfaces 2021, 13, 25836–25849] revealed a new concept toward blocking the Ni-migration pathway by placing Zn2+ (which lacks octahedral site preference) in the tetrahedral site of the Li-layer, which, otherwise, serves as an intermediate site for the Ni-migration to the Li-layer. This, nearly completely, suppressed the Ni-migration, despite being deep delithiated up to a potential of 4.7 V (vs Li/Li+) and, thus, resulted in significant improvement in the high-voltage cyclic stability. In this regard, by way of conducting operando synchrotron X-ray diffraction, operando stress measurements, and 3D atom probe tomography, the present work throws deeper insights into the effects of such Zn-doping toward enhancing the structural–mechanical–compositional integrity of Li-NMCs upon being subjected to deep delithiation. These studies, as reported here, have provided direct lines of evidence toward notable suppression of the variations of lattice parameters of Li-NMCs, including complete prevention of the detrimental “c-axis collapse” at high states-of-charges and concomitant slower-cum-lower electrode stress development, in the presence of the Zn-dopant. Furthermore, the Zn-dopant has been found to also prevent the formation of Ni-enriched regions at the nanoscaled levels in Li-NMCs (i.e., Li/Ni-segregation or “structural densification”) even upon being subjected to 100 charge/discharge cycles involving deep delithiation (i.e., up to 4.7 V). Such detailed insights based on direct/real-time lines of evidence, which reveal important correlations between the suppression of Ni-migration and high-voltage compositional–structural–mechanical stability, hold immense significance toward the development of high capacity and stable “layered” Li-TM-oxide based cathode materials for the next-generation Li-ion batteries.

Tuning the optoelectronic properties of emerging solar absorbers through cation disorder engineering

“…It can be seen that techniques commonly used to characterize cation disorder now mainly rely on the comparison between ordered and disordered samples, while a more direct way to probe cation arrangements is still lacking. Techniques such as high-resolution transmission electron microscopy (HRTEM) or atom probe tomography (APT), 75 which can visualize different atoms with sub-nanometer resolution, can be useful for more directly characterizing cation disorder. However, the critical challenge for these techniques will be to characterize the materials without altering them during sample preparation or during the measurement itself.…”

Recent advances in battery characterization using in situ XAFS, SAXS, XRD, and their combining techniques: From single scale to multiscale structure detection

“…The operando XRD tests and the Rietveld refinement results confirmed that Co doping can extend the lattice and decrease particle size, which is conducive to cathodic reactions and promotes synergistic catalytic effects, and then improve electrochemical performance. [118] To investigate the influence of Zn doping on the structural-mechanical-compositional integrity of Li-TM-oxide-based cathode materials (Li-NMC) after deep lithium removal, operando XRD was used to systematically study the changes of lattice parameters (Figure 7B) by Sharma et al [119] Typically, serious structural degradation occurs for Ni-rich cathode materials when operated in high-temperature condition, which often leads to severe performance degradation. Lee.…”

“…[ 118 ] To investigate the influence of Zn doping on the structural‐mechanical‐compositional integrity of Li‐TM‐oxide‐based cathode materials (Li‐NMC) after deep lithium removal, operando XRD was used to systematically study the changes of lattice parameters (Figure 7B) by Sharma et al. [ 119 ] Typically, serious structural degradation occurs for Ni‐rich cathode materials when operated in high‐temperature condition, which often leads to severe performance degradation. Lee.…”

“…Reproduced with permission. [ 119 ] Copyright 2023, American Chemical Society. (C) Voltage profiles and XRD patterns were obtained by in‐situ XRD analysis using in‐situ half‐cells of the fresh NCA cathode (second cycle) and 60°C‐stored NCA cathode (cycled after the refreshing process) during charging and discharging at C/7.…”