Interfacial Engineering of Dry-Processed High-Loading LiNi_0.5Mn_1.5O₄Cathodes: Additive Dissolution and Bilayer Cathode–Electrolyte Interphase toward Stable High-Voltage Lithium Metal Batteries

Lithium metal batteries (LMBs) employing LiNi_0.5Mn_1.5O₄ (LNMO) cathodes (5 V-class, vs Li⁺/Li) exhibit significant potential for next-generation energy storage owing to their high theoretical energy density and high-voltage capability. However, the practical development of LNMO/Li batteries is severely constrained by the incompatibility of carbonate-based electrolytes with highly reactive cathodes and anodes. To solve this, we propose a novel electrode–electrolyte interfacial engineering strategy: a dry electrode fabrication process is implemented, in which vapor-grown carbon fibers (VGCFs) are coated with polytetrafluoroethylene (PTFE) to passivate carbon active sites, thereby effectively mitigating electrolyte oxidation at high voltages. Simultaneously, lithium nonafluorobutanesulfonate (LNBS) and succinonitrile (SN) are incorporated as functional additives into the cathode. Mild heating during electrode fabrication melts these additives, enhancing the flexibility and mechanical integrity of the electrode. These additives partially dissolve during cell operation. LNBS contains SO₃^– polar groups that facilitate the dissociation of lithium salt ion pairs. Its electronegativity anchors transition metal ions onto the LNMO cathode surface, forming a Ni–S-containing adsorption layer that suppresses their migration into the electrolyte. Meanwhile, lithium difluoro(oxalato)borate (LiODFB) preferentially decomposes at the cathode interface, cooperatively forming a protective bilayer (an outer inorganic-rich layer and an inner Ni–S-containing absorption layer). At the anode, Li-SN (formed via coordination between SN and Li⁺) decomposes to generate an inorganic-rich solid electrolyte interphase (SEI), stabilizing lithium plating/stripping. These synergistic modifications enable LNMO/Li batteries with high-loading cathodes (20 mg cm^–2) to achieve 88.6% capacity retention after 400 cycles at 0.5 C, with an average Coulombic efficiency of 99.44%. Moreover, when charged to 4.85 V, the cell maintains an open-circuit voltage above 4.68 V for over 1400 h, demonstrating exceptional cycling and storage stability with conventional carbonate-based electrolytes.