Abstract
Two-phase heterostructure with rich phase boundaries holds great potential in engineering advanced electrode materials. However, current heterostructures are largely generated by introducing exotic cations or anions, complicating synthetic procedures and disturbing real insights into the intrinsic effect of heterostructure. Herein, nanosized monometallic selenides heterostructures are developed by precisely controlled selenylation of metal organic frameworks, which are implanted into in-situ formed carbon (NiSe/NiSe2@C, CoSe/CoSe2@C). The disordered atoms arrangement at two-phase boundary leads to the redistribution of interfacial charge and generation of lattice distortions, promoting easy adsorption and swift transfer of Li+, and providing extra active sites. As a proof of concept, the NiSe/NiSe2@C exhibits far surpassing lithium storage properties to single-phase counterparts (NiSe@C and NiSe2@C), including higher reversible capacity of 1015.5 mAh g−1, better rate capability (500.8 mAh g−1 at 4 A g−1), and superior cyclic performance. As expected, the NiSe/NiSe2@C manifests lower charge transfer resistance, higher Li+ diffusion coefficient, and accelerated capacitive kinetics. Ex-situ X-ray diffraction, high-resolution transmission electron microscopy, and selected area electron diffraction combined with differential capacity versus voltage plots reveal multi-step redox mechanism of NiSe/NiSe2@C and the reason of conspicuous capacity enhancement. This work demonstrates the enormous potential of monometallic monoanionic heterostructure in energy-related field.
Highlights
Lithium-ion batteries (LIBs) are currently dominant energy storage devices towards commercial requirements owing to the advantages of high energy density, long lifespan, high safety [1,2]
The monometallic selenides heterostructures surrounded by conductive carbon matrix (NiSe/NiSe2@C, CoSe/CoSe2@C) were synthesized, by adjusting the ratio of MOF precursor to selenium powder during calcination
The NiSe/NiSe2@C delivers high reversible capacity (1015.5 at 0.1 A g-1), excellent rate capability (500.8 at 4 A g-1), and long-term cyclic stability (540.3 mAh g−1 after 1000 cycles at 1 A g-1). This enhanced lithium storage properties should be due to the heterogeneous interface between NiSe and NiSe2 domains with electrons rearrangement, which promotes rapid charge transfer and ion adsorption, as well as increases the electrochemically active sites, improving the reaction kinetics
Summary
Lithium-ion batteries (LIBs) are currently dominant energy storage devices towards commercial requirements owing to the advantages of high energy density, long lifespan, high safety [1,2]. XRD patterns confirm that pure-phase NiSe and NiSe2 are respectively obtained with mass ratios of Ni-MOF: Se as 3:1 and 3:3. The superior Li+ storage properties of NiSe/NiSe2@C could be attributed to the abundant phase boundaries with distortions and defects inside the NiSe/NiSe2 heterostructure, which could facilitate the adsorption and transfer of Li+ ions and improve reaction kinetics.
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