Unusual Li2O sublimation promotes single-crystal growth and sintering

Abstract

Li₂O is rarely used for cathode material synthesis due to its high melting point (1,438 °C). Here we discover that Li₂O can sublimate at 800–1,000 °C under ambient pressure, opening new possibilities for cathode synthesis. We propose a mechanism that enables synthesis of single crystals—such as LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) or LiNi_0.9Mn_0.05Co_0.05O₂ (NMC90)—without direct contact with Li₂O salts. We show that Li₂O vapour successfully converts spent polycrystalline NMC811 into segregated single crystals without milling or post-treatment. The Li₂O vapour, derived from Li₂O solids, diffuses rapidly and reacts with precursors, mimicking a molten-salt environment, which facilitates single-crystal growth. The chemical lithiation process continuously drives Li₂O sublimation, sintering the crystals. Single crystals derived from Li₂O and fresh precursors or spent polycrystals exhibit outstanding cycling after 1,000 cycles in full cells. The demonstrated Li₂O sublimation and its universal role in promoting single-crystal growth provides an effective approach for single-crystal synthesis, scale-up and recycling.