Sustainable high-energy-density Li-Mn-O layered cathode via metastable synthetic kinetics

The electrochemical stability of metastable lithium-rich layered cathodes is intrinsically governed by their synthetic history, yet the correlation between ion-exchange thermodynamics and structural evolution remains elusive. Here, using layered P3-Na_0.6[Li_0.2Mn_0.8]O₂ as a precursor, the spontaneous ion-exchange synthesis of O3-Li_0.6[Li_0.2Mn_0.8]O₂ (O3-LLM RT) at room temperature yields one of the most promising layered Li-Mn-O cathodes reported to date in LiPF₆-based carbonate electrolyte at room temperature. However, elevated synthesis temperatures induce manganese ion migration, which hinders the reversible interlayer migration of Li⁺ into the transition metal layers. This structural impediment triggers irreversible lattice oxygen activation and degrades structural stability (e.g. at 280°C, denoted the high-temperature O3-LLM sample as (O3-LLM HT)). Consequently, the perfect layered O3-LLM RT cathode exhibits a high specific capacity of 250 mAh/g with an excellent cycling stability of 88.1% capacity retention (vs. the 51.9% for O3-LLM HT) after 400 cycles at 2.0-4.8 V, ranking at the top of the Li-Mn-O layered cathodes. These findings provide insights into the design and optimization of metastable materials for high-energy-density batteries.