High-rate rare-earth-based high-entropy Co-free high-Ni cathodes for high-performance lithium-ion batteries

Abstract

In electric transportation and energy storage systems, the development of Co-free Ni-rich layered cathode materials that can maintain high specific discharge capacity and cycling stability under high-rate discharging conditions is critical to the practical application of advanced lithium-ion batteries (LIBs). However, the non-equilibrium delithiation reaction induced by high-rate discharge conditions and the pursuit of low/no cobalt (low cost, low toxicity) leads to hindered interfacial and internal kinetics of Li⁺ and structural degradation of the cathode. In this work, we have designed a family of rare-earth-based high-entropy Co-free high-Ni cathode materials LiNi_0.9Mn_0.02Al_0.02Mg_0.02Ti_0.02Si_0.02O₂ (Lu substituting Si, Ti, Mg, and Al, respectively) for constructing a promising high-rate rare-earth high-entropy Co-free high-Ni layered cathode LiNi_0.9Mn_0.02Al_0.02Mg_0.02Ti_0.02Lu_0.02O₂ (HE-Lu). The “entropy stabilization” effect is maximized by optimizing the synergistic relationship between the rare-earth elements and the high-entropy doping elements. The pinning effect of rare-earth elements suppresses the inconsistency of Li⁺ intercalation under high-rate discharging. High-entropy doping can significantly inhibit the formation of microcracks at high current densities, smooth the H2–H3 detrimental phase transition and induce the formation of an ultra-thin and stable cathode electrolyte interface (CEI) on the cathode. The structure of the LiNi_0.9Mn_0.02Al_0.02Mg_0.02Ti_0.02Lu_0.02O₂ cathode remains ultra-stable even under harsh conditions and at a high cut-off voltage (4.7 V). The discharge capacity of the HE-Lu cathode is 218.5 mA h g⁻¹ at 0.2C, and the capacity retention rate is maintained at 84.8% and 81.2% under 1C charging and 5C discharging (1 C/5C) rates even after 1500 cycles (2.7–4.3 V) and 300 cycles (2.7–4.7 V), respectively. The full cell has a high capacity retention of 88.3% even after 1000 cycles. This work provides a promising strategy for designing Co-free, high-Ni cathodes in high-rate lithium-ion batteries.