Single Crystal Sodium Layered Oxide Achieves Superior Cyclability at High Voltage

Large-sized single-crystal O3-typed layer-structured manganese-based transition metal oxides Na[Ni_0.3Mn_0.35Cu_0.1Ti_0.25]O₂ was successfully synthesized. They have a high ion diffusion without hindering by the crystal gap. Meanwhile, the uneven sodium ions insertion and extraction inside the particles with oxygen release will be alleviated. It can efficiently increase the cycling lifespan by alleviating the sides reaction from electrolytes.

Abstract

High-energy density and long-lifespan have been a long-standing target toward the high-voltage sodium batteries requirement. It is important and essential to explore cathode materials, which can realize high voltage stability. Large-sized single-crystal O3-typed Na[Ni_0.3Mn_0.35Cu_0.1Ti_0.25]O₂ is thus designed and successfully synthesized by molten salt-assist calcination method. The high-orientation crystal lattice without grain boundaries cannot only accelerate the ion diffusion rate and electronic conductivity, but also minimize the occurrence of phase transitions and mechanical stress to address the crystal oxygen loss. Meanwhile, the large-exposed stable (003) crystal plane can alleviate the electrolyte attacking and corrosions, forming a stable interface structure. The obtained material exhibits capacity retention rates of 84.4% and 90.1% after 200 cycles at 0.5 C and 1 C, respectively. Once coupled with hard carbon as anode, the full-cell retains a high 81.5% capacity retention after 1000 cycles at 2 C.