AbstractAiming for increased nickel and lower cobalt content in layered transition metal oxide cathodes (NCM) is a feasible strategy for achieving increased energy density and cost competitiveness in commercial lithium‐ion batteries. However, the practical long‐term cycling of NCM cathodes suffers from severe capacity degradation due to irreversible interface phase transformation and unavoidable crack formation. Herein, an in situ modification strategy is used to form a uniform and conformal Li_1.8Sc_0.8Ti_1.2(PO₄)₃ (LSTP) protective layer by interconnecting the single‐crystal‐layered LiNi_0.6Co_0.1Mn_0.3O₂ (SC‐NCM) particles. LSTP surface modification helps to construct a robust cathode‐electrolyte interphase thin film between the cathode and the electrolyte, which can prevent SC‐NCM corrosion by electrolyte, and the stability of the mechanics can improve the intergranular cracks caused by long cycles under harsh conditions. Moreover, the LSTP conductive modification layer facilitates the lithium‐ion transport among cathode particles, effectively enhancing the rate capability. Impressively, the LSTP modified SC‐NCM exhibits a high reversible capacity of 144.3 mAh g⁻¹ at the high discharge rate of 5 C and maintains a capacity retention of 90.27% even at the ultrahigh charge voltage of 4.6 V operation after 500 cycles. Moreover, in a pouch‐type full battery, the graphite/LSTP modified SC‐NCM maintains a capacity retention of 89.6% after 1700 cycles.