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

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_0.6Co_0.2Mn_0.2O₂, 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_0.8Co_0.1Mn_0.1O₂ 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.