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-Na0.6[Li0.2Mn0.8]O2 (P3-NLM) as a precursor, the spontaneous ion exchange synthesis of O3-Li0.6[Li0.2Mn0.8]O2 (O3-LLM RT) yields one of the most promising layered Li–Mn–O cathodes reported to date within 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 as the O3-LLM HT). Consequently, the perfect layered O3-LLM RT cathode exhibits a high specific capacity of 250 mAh/g with 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.