Chemically Integrated Multiwalled Carbon Nanotubes/Zinc Manganate Nanocrystals as Ultralong-Life Anode Materials for Lithium-Ion Batteries

Abstract

Hybrid nanostructures based on carbon nanotubes and mixed transition-metal oxides hold a great promise as highperformance electrode materials for next-generation lithium-ion batteries. In this work, we report the synthesis of chemically integrated MWCNT/ZnMn 2 O 4 (MZMO) hybrids via a polyol method and subsequent thermal annealing treatment. Benefiting from the larger specific surface area, strongly coupled interaction and synergic effect between ZnMn 2 O 4 nanocrystals and MWCNT, the MZMO hybrids exhibit improved electrochemical performance, with a high reversible specific capacity, and excellent rate capability, as well as a superior cycle stability. After 100 cycles, the MZMO2 demonstrates a reversible capacity of 847 mA h g −1 at a current density of 400 mA g −1 . Even at 1600 mA g −1 up to 1000 cycles, the reversible capacity still preserves 527 mAh g −1 , which is much higher than the theoretical capacity of graphite.

Micro‐/Mesoporous Zinc–Manganese Oxide/Graphene Hybrids with High Specific Surface Area: A High‐Capacity, Superior‐Rate, and Ultralong‐Life Anode for Lithium Storage

“…X‐ray photoelectron spectroscopy (XPS) was conducted to analyze the chemical composition and valence state of the hybrid. As shown in Figure b, two peaks located at binding energies (BEs) of 1044.7 and 1021.6 eV can be ascribed to Zn 2p 1/2 and Zn 2p 3/2 respectively, which is consistent with Zn II of ZnMn 2 O 4 . The Mn 2p spectrum shown in Figure c depicts two strong peaks at BEs of 653.7 and 641.7 eV, which can be attributed to Mn 2p 1/2 and Mn 2p 3/2 , respectively .…”

“…Typically, Zn 2+ and Mn 2+ ions strongly couple with the oxygen‐containing functional groups of graphene oxide (GO), such as the hydroxy and carboxy groups. In the process of heating at reflux, zinc–manganese oxide is formed on the surface of graphene due to a coordination effect . Moreover, the GO sheets are partially reduced.…”

“…During the first cycle, the strong peak at a voltage of 0.11 V is attributed to the transformation of Mn 2+ into Mn 0 and Zn 2+ into Zn 0 implanted in the matrix of Li 2 O, and this is followed by the formation of a Li–Zn alloy . In the anodic process, there is a broad peak centered at a voltage of 1.31 eV that is derived from the oxidation of Mn 0 to Mn 2+ and Zn 0 to Zn 2+ along with decomposition of the Li 2 O matrix . During the following cycle, the peak at a voltage of 0.11 V shifts to 0.35 V and is broadened relative to the size of the first one.…”

“…The Coulombic efficiency of the Zn‐Mn‐O/G hybrids is 70.9 % in the first cycle. The corresponding irreversible loss of about 29.1 % can be ascribed to the generation of a SEI layer, which traps the lithium ions, and a partial irreversible conversion reaction the of Zn‐Mn‐O/G electrode, such as the reduction of Mn 3+ to Mn 2+ …”

“…Among these promising anode materials, manganese‐based oxides have recently shown great advantages because of their low costs (manganese is about 20 times cheaper than cobalt), resource abundance, environmental friendliness, and lower operation voltage relative to that of cobalt‐ or iron‐based oxides . Besides simple binary manganese‐based oxides, spinel‐structured ZnMn 2 O 4 can store energy through a conversion reaction and alloying/dealloying between Zn and Li + (Zn+Li + +e − ↔LiZn), which results in a theoretical capacity of 1024 mAh g −1 . Unfortunately, the intrinsically low electronic/ionic conductivity of ZnMn 2 O 4 as well as the large volume change that occurs during the lithium intercalation and de‐intercalation process leads to poor cycling and rate performance.…”