Formation of uniform porous yolk-shell MnCo2O4 microrugby balls with enhanced electrochemical performance for lithium storage and the oxygen evolution reaction

Mixed transition metal oxides with favorable electrochemical properties are promising electrode materials in energy storage and conversion systems. In this work, uniform porous yolk-shell MnCo₂O₄ (denoted as YSM-MCO) microrugby balls have been synthesized by simple annealing treatment of metal carbonates with a microrugby ball shape in air. Benefiting from the desired porous structure and composition, the as-synthesized YSM-MCO exhibits enhanced electrochemical performance when investigated as anode materials for lithium-ion batteries and electrocatalysts for the oxygen evolution reaction. The YSM-MCO demonstrates remarkable lithium storage properties with a good cycling stability (94% capacity retention over 200 cycles at 0.5 A g^-1) and superior rate capability (414 mA h g^-1 at 5 A g^-1). In addition, the YSM-MCO also exhibits better OER activity than most of the reported MnCo₂O₄-based electrocatalysts.

β-MnO2 /Metal-Organic Framework Derived Nanoporous ZnMn2 O4 Nanorods as Lithium-Ion Battery Anodes with Superior Lithium-Storage Performance

Nanoporous ZnMn₂ O₄ nanorods have been successfully synthesized by calcining β-MnO₂ /ZIF-8 precursors (ZIF-8 is a type of metal-organic framework). If measured as an anode material for lithium-ion batteries, the ZnMn₂ O₄ nanorods exhibit an initial discharge capacity of 1792 mA h g^-1 at 200 mA g^-1 , and an excellent reversible capacity of 1399.8 mA h g^-1 after 150 cycles (78.1 % retention of the initial discharge capacity). Even at 1000 mA g^-1 , the reversible capacity is still as high as 998.7 mA h g^-1 after 300 cycles. The remarkable lithium-storage performance is attributed to the one-dimensional nanoporous structure. The nanoporous architecture not only allows more lithium ions to be stored, which provides additional interfacial lithium-storage capacity, but also buffers the volume changes, to a certain degree, during the Li⁺ insertion/extraction process. The results demonstrate that nanoporous ZnMn₂ O₄ nanorods with superior lithium-storage performance have the potential to be candidates for commercial anode materials in lithium-ion batteries.

Mesoporous ZnMn2O4 Microtubules Derived from a Biomorphic Strategy for High-Performance Lithium/Sodium Ion Batteries

ZnMn₂O₄ microtubules (ZMO-MTs) with a mesoporous structure are fabricated by a novel yet effective biomorphic approach employing cotton fiber as a biotemplate. The fabricated ZMO-MT has approximately an inner diameter of 8.5 μm and wall thickness of 1.5 μm. Further, the sample of ZMO-MT displays a large specific surface area of 48.5 m² g^-1. When evaluated as a negative material for Li-ion batteries, ZMO-MT demonstrates an improved cyclic performance with discharge capacities of 750.4 and 535.2 mA h g^-1 after 300 cycles, under current densities of 200 and 500 mA g^-1, respectively. Meanwhile, ZMO-MT exhibits superior rate performances with high reversible discharge capacities of 614.7 and 465.2 mA h g^-1 under high rates of 1000 and 2000 mA g^-1, respectively. In sodium ion batteries applications, ZMO-MT delivers excellent high discharge capacities of 102 and 71.4 mA h g^-1 after 300 cycles under 100 and 200 mA g^-1, respectively. An excellent rate capability of 58.2 mA h g^-1 under the current density of 2000 mA g^-1 can also be achieved. The promising cycling performance and rate capability could be benefited from the unique one-dimensional mesoporous microtubular architecture of ZMO-MT, which offers a large electrolyte/electrode accessible contact area and short diffusion distance for both of ions and electrons, buffering the volume variation originated from the repeated ion intercalation/deintercalation processes.

Rice-shaped porous ZnMn2O4 microparticles as advanced anode materials for lithium-ion batteries

Novel rice-shaped porous ZnMn₂O₄ microparticles made of nanoparticles were prepared by the calcination of Zn_0.33Mn_0.67CO₃ precursors synthesized using a facile triethanolamine-assisted solvothermal method.

A new approach to improve the electrochemical performance of ZnMn2O4 through a charge compensation mechanism using the substitution of Al3+ for Zn2+

ZnMn₂O₄ and Zn_1−xAl_xMn₂O₄ were synthesized by a spray drying process followed by an annealing treatment. Their structural and electrochemical characteristics were investigated by SEM, XRD, XPS, charge–discharge tests and EIS. XPS data indicate that the substitution of Al³⁺ for Zn²⁺ causes manganese to be in a mixed valence state by a charge compensation mechanism. Moreover, the presence of this charge compensation significantly improves the electrochemical performance of Zn_1−xAl_xMn₂O₄, such as increasing the initial coulombic efficiency, stabilizing the cycleability as well as improving the rate capability. The sample with 2% Al doping shows the best performance, with a first cycle coulombic efficiency of 69.6% and a reversible capacity of 597.7 mA h g⁻¹ after 100 cycles. Even at the high current density of 1600 mA g⁻¹, it still retained a capacity of 558 mA h g⁻¹.

This work reports the nonequivalent substitution of ZnMn₂O₄. This is a new approach to improve the electrochemical performance of ZnMn₂O₄ through a charge compensation mechanism using the substitution of Al³⁺ for Zn²⁺.

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.