Graphene-oxide-wrapped ZnMn₂O₄ as a high performance lithium-ion battery anode

Cation distribution between tetrahedral and octahedral sites within the ZnMn₂O₄ spinel lattice, along with microstructural features, is affected greatly by the temperature of heat treatment. Inversion parameters can easily be tuned, from 5%-19%, depending on the annealing temperature. The upper limit of inversion is found for T = 400 °C as confirmed by x-ray powder diffraction and Raman spectroscopy. Excellent battery behavior is found for samples annealed at lower temperatures; after 500 cycles the specific capacity for as-prepared ZnMn₂O₄ is 909 mAh g^-1, while ZnMn₂O₄ heat-treated at 300 °C is 1179 mAh g^-1, which amounts to 101% of its initial capacity. Despite the excellent performance of a sample processed at 300 °C at lower charge/discharge rates (100 mAh g^-1), a drop in the specific capacity is observed with rate increase. This issue is solved by graphene-oxide wrapping: the specific capacity obtained after the 400th cycle for graphene-oxide-wrapped ZnMn₂O₄ heat-treated at 300 °C is 799 mAh g^-1 at a charge/discharge rate 0.5 A g^-1, which is higher by a factor of 6 compared to samples without graphene -oxide wrapping.