Flexible and Scalable Magnesium Replenishment in NCM Cathode Enabled by Mobile Mg2+ Enriched MgV2O4

Abstract A small amount of Mg 2+ doping can show a significant effect on the surface protection and structural stability of the nickel‐rich layered oxide cathode, but the traditional doping process involves completely changing the initial raw material proportions with subsequent trial and error adjustments. Herein, a concept of Mg 2+ release film is proposed, in which Mg 2+ can easily permeate into various layered oxide cathodes during cycling. Meanwhile, to realize this concept, MgV 2 O 4 with mobile Mg 2+ in the structures and then fabricated a self‐supporting MgV 2 O 4 membrane are synthesized. As a protective layer for cathode, the MgV 2 O 4 membrane release Mg 2+ in situ during the electrochemical process, providing structural reinforcement to the cathode surface as a “pillar” within the lattice. Thanks to the MgV 2 O 4 membrane, the cycle life of LiNi o.8 Co 0.1 Mn 0.1 O 2 (NCM811) coupled with the MgV 2 O 4 interlayer at 1.0 C is increased by 1.9 times compared to bare NCM811. Furthermore, this novel Mg 2+ releasing film demonstrates excellent versatility, enabling other nickel‐based layered oxide to achieve a high‐capacity retention of 86.4% after 800 cycles at 1.0 C. This approach provides scalable cathode protection and repair strategies for commercially viable batteries.