In Situ‐Constructed Elastomeric Interphase for Grain Boundary Stabilization in High‐Voltage Layered Oxide Cathodes

ABSTRACT Layered oxide cathodes are a leading class of high‐energy‐density electrode materials for lithium‐ion batteries, but their long‐term stability at high voltages is compromised by chemical corrosion and mechanical stress at grain boundaries. Here, we report the construction of an elastic and voltage‐tolerant poly(urea‐siloxane) (PUSi) coating via the in situ polymerization of amine‐terminated polydimethylsiloxane and toluene diisocyanate (TDI). This polymer acted as a conformal artificial interphase that stabilized the secondary‐particle surface and internal primary‐particle surfaces. The PUSi layer acted as a stable chemical barrier that isolated cathode interfaces from direct contact with the electrolyte. This suppressed interfacial side reactions and inhibited the layered‐to‐spinel phase transformation. The tailorable elasticity of the PUSi layer allowed it to accommodate cyclic volumetric variations and suppress intergranular cracking during high‐voltage cycling. When applied to LiNi 0.6 Co 0.2 Mn 0.2 O 2 , the cathode showed a capacity retention of 81.2% after 450 cycles in coin cells and 82.4% after 200 cycles in Li‐metal pouch cells under a cut‐off voltage of 4.5 V. The generality of this approach was demonstrated by using it to coat LiNi 0.8 Co 0.1 Mn 0.1 O 2 and lithium‐rich layered oxides. This work provides a scalable and eco‐friendly route for engineering grain boundaries and interfacial stability in high‐energy cathode systems.