Preemptive Interfacial Engineering Through Biphasic Catalyst and Potential Difference for Stable High‐Voltage NCM811 Batteries

The pursuit of high‐voltage Ni‐rich LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NCM811) has been constrained by severe interfacial instability. Herein, we demonstrate a preemptive interface engineering strategy enabled by a MoS 2 ‐catalyzed Li 2 CO 3 (MCL) additive. Benefiting from the synergistic effect of biphasic MoS 2 catalyst and the intrinsic potential difference between MCL and delithiated NCM811, the effective decomposition voltage of Li 2 CO 3 is reduced from >4.7 V to 3.9 V. Such low‐potential activation enables the in situ formation of a thin, uniform, and inorganic‐rich (Li 2 O/Li 2 CO 3 ) cathode–electrolyte interphase (CEI) prior to both native CEI buildup and the detrimental H2/H3 phase transitions in NCM811. Meanwhile, Li + released from Li 2 CO 3 compensate irreversible lithium loss during cycling, while Li 2 CO 3 decomposition products promote the formation of a robust solid electrolyte interphase (SEI). This dual interfacial regulation on both electrodes synergistically reinforces the interfacial integrity of the battery system. As a result, a 2.5 Ah‐NCM811||Si/C cylindrical cell incorporating MCL delivers a capacity retention of 85.0% after 600 cycles at 4.2 V and 68.7% after 200 cycles at 4.5 V, substantially outperforming the corresponding blank cells (78.6% and 51.8%, respectively). This work overcomes the intrinsic ultrahigh‐voltage decomposition limitation of Li 2 CO 3 and establishes a general preemptive strategy for developing durable Ni‐rich cathodes under aggressive high‐voltage operation.