<p>High-energy-density lithium-ion batteries for extreme conditions require cathodes that remain stable under harsh operation, including ultrahigh cutoff voltage and extreme temperatures. For Ni-rich layered cathodes, raising the charge voltage from 4.3 V to 4.8 V (versus Li⁺/Li) increases the energy density, yet this sacrifices cycling stability and remains challenging. Here we report a dopant-pairing method that achieves highly enriched Ti⁴⁺ (~9-nm surface layer) in LiNi_0.8Co_0.1Mn_0.1O₂ facilitated by Na⁺, enabling significantly enhanced high-voltage cyclability. Such high surface Ti⁴⁺ concentrations are unattainable without pairing Na⁺, representing a form of supersaturation within the layered cathode matrix. The enhanced stability is linked to improved structural integrity and reduced cathode–electrolyte side reactions (for example, O₂ and CO₂ evolution). In addition, ion transport is better preserved even after prolonged cycling at 4.8 V. This work highlights the power of supersaturated high-valence <i>d</i>⁰ cation <i>M</i>^<i>z</i>+ (<i>z</i> ≥ 4) in modifying the cathode–electrolyte interactions and degradation pathway.</p>