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

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

Thin Free-Standing Sulfide/Halide Bilayer Electrolytes for Solid-State Batteries Using Slurry Processing and Lamination

Thin-film solid electrolytes with wide electrochemical stability windows are required to develop solid-state lithium (Li) metal batteries with high energy densities. In this work, free-standing Li3InCl6 (30 μm)|Li6PS5Cl (30 μm) bilayer thin films are prepared by slurry casting, drying, and lamination. This combination of solid electrolytes is stable at both the cathode interface (high voltages) and anode interface (low voltages). The bilayer thin films exhibit >10× lower area-specific resistance than thick (∼1 mm) pellets fabricated by traditional powder pressing. The free-standing bilayer electrolytes are laminated onto electrodeposited LiCoO2 cathodes. Subsequently a Li–In anode is laminated on top of the stack, and stable cycling of all-solid-state batteries is demonstrated. Because of reduced ohmic losses, cells fabricated with thin-film electrolytes exhibit lower cell polarization and improved rate capability compared with cells with a traditional pellet geometry. This study offers a general strategy to fabricate free-standing bilayer thin-film solid electrolytes for high-energy-density solid-state batteries