Trace multi-cation high-entropy engineering enables ultra-stable cobalt-free LiNiO₂ with >230 mAh/g

The cobalt-free LiNiO₂ (LNO) cathode, composed solely of transition metal nickel, stands out as a prime candidate for next-generation commercial cathodes, offering an exceptional theoretical capacity of 275 mAh/g, cost efficiency, and environmental sustainability. Unlike LiNi_xMn_yCo₂O₂ (NMC) counterparts, LiNiO₂ (LNO) cathode is plagued by rapid capacity degradation and safety risks due to absence of Co/Mn, which act as structural stabilizers ('rivets') in transition metal layer. This deficiency induces severe anisotropic lattice distortion and multi-phase transitions during charge/discharge cycles. These distortions are exacerbated at elevated temperatures (>45 °C) and at high de-lithiation state with initial discharge capacities exceeding 230 mAh/g. To mitigate these issues, we introduced a high-entropy engineering approach for LNO, exemplified by LiNi_0.98Mo_0.005Nb_0.005Ti_0.005Mg_0.005O₂ (LNO-2 %HE). In situ XRD, synchrotron XAS and ex situ analyses reveal that the compositional complexity of LNO-2 %HE enhances structural disorder and amorphous character, which suppresses high-voltage phase transition. This design achieves 96.1 % capacity retention over 100 cycles at 25 °C and 97.5 % retention after 50 cycles at 45 °C, alongside an initial discharge capacity of 238 mAh/g at 0.1C. Furthermore, improved lattice oxygen stability in LNO-2 %HE inhibits oxygen release during thermal phase transitions, significantly enhancing safety. This strategy advances the viability of LNO cathode for high-energy-density batteries.