Wide-temperature operation is becoming essential for high-energy Li-ion batteries deployed in extreme environments, thereby requiring cathode materials capable of sustaining high energy density and stable electrochemical reactions under thermal fluctuations. Accordingly, high-Ni layered oxide cathodes have attracted considerable attention due to the high specific capacity and elevated operating voltage. However, their practical application across a wide temperature range remains constrained by temperature-induced degradation. At elevated temperatures, lattice expansion, oxygen release, and irreversible structural evolution within the cathode bulk undermine structural stability. Meanwhile, accelerated electrolyte decomposition further promotes surface reconstruction, transition-metal dissolution, and uncontrolled interfacial layer growth at the cathode/electrolyte interface. At low temperatures, sluggish Li-ion transport throughout the cathode bulk and electrolyte is accompanied by poor interfacial desolvation/charge-transfer kinetics. Understanding these coupled degradation processes is essential for improving the wide-temperature performance of high-Ni layered cathodes. This review therefore elucidates their temperature-dependent degradation mechanisms and discusses recent progress in optimization strategies. Beyond conventional doping and coating, functional interfacial layers with intrinsic physical responses to service-temperature variations is emphasized as an emerging approach for regulating interfacial charge transfer and lattice strain evolution. These insights are expected to guide the design of wide temperature high-Ni cathodes with improved safety and durability.