Morphology engineering of self-assembled porous zinc manganate hexagons for lithium ion storage

Porous zinc manganate (ZnMn₂O₄), which is typically fabricated from the decomposition of its carbonates, promises a high-performance anode material for lithium ion batteries (LIBs). Most of porous ZnMn₂O₄ in literature presents in sphere morphology. Herein, a unique type of porous ZnMn₂O₄ hexagons with a side length of about 2 μm and a BET specific surface area of 34.19 m² g⁻¹, assembled by ca. 100 nm nanoparticles, has been successfully fabricated by a solvothermal reaction with subsequent calcination of the self-assembled catena-poly intermediates. The growth mechanism of the solvothermal products has been systematically investigated by adjusting the stoichiometric ratio of oxalic acid, the type of the salt source and acid additive, and the reaction media, resulting in a wide spectrum of morphologies ranging from hexagon, porous sphere, hourglass to belt. The hexagon precursor was calcined in air to obtain the porous structure, attributed to the spaces between nanoparticle assemblies. When used for lithium-ion storage, the as-prepared porous ZnMn₂O₄ hexagons-based anode exhibits a reversible capacity of 716 mA h g⁻¹ after 200 cycles at 100 mA g⁻¹, outperforming the pure porous Mn₂O₃ hexagons and the non-porous ZnMn₂O₄ hexagons.