Suppressing high voltage chemo-mechanical degradation in single crystal nickel-rich cathodes for high-performance all-solid-state lithium batteries

Sulfide-based all-solid-state lithium batteries suffer from electrochemo-mechanical damage to Ni-rich oxide-based cathode active materials (CAMs), primarily caused by severe volume changes, results in significant stress and strain, causes micro-cracks and interfacial contact loss at potentials > 4.3 V(vs. Li/Li⁺). Quantifying micro-cracks and voids in CAMs can reveal the degradation mechanisms of Ni-rich oxide-based cathodes during electrochemical cycling. Nonetheless, the origin of electrochemical-mechanical damage remains unclear. Herein, We have developed a multifunctional PEG-based soft buffer layer (SBL) on the surface of carbon black (CB). This layer functions as a percolation network in the single crystal LiNi_0.83Co_0.07Mn_0.1O₂ and Li₆PS₅Cl composite cathode layer, ensuring superior ionic conductivity, reducing void formation and particle cracking, and promoting uniform utilization of the cathode active material in all-solid-state lithium batteries (ASSLBs). High-angle annular dark-field STEM combined with nanoscale X-ray holo-tomography and plasma-focused ion beam scanning electron microscopy confirmed that the PEG-based SBL mitigated strain induced by reaction heterogeneity in the cathode. This strain produces lattice stretches, distortions, and curved transition metal oxide layers near the surface, contributing to structural degradation at elevated voltages. Consequently, ASSLBs with a LiNi_0.83Co_0.07Mn_0.1O₂ cathode containing LCCB-10 (CB/PEG mass ratio: 100/10) demonstrate a high areal capacity (2.53 mAh g⁻¹/0.32 mA g⁻¹) and remarkable rate capability (0.58 mAh g⁻¹ at 1.4 mA g⁻¹), with 88% capacity retention over 1000 cycles.