Double-shelled nanoporous NiO nanocrystal doped MnO/Ni network for high performance lithium-ion battery

Hierarchical Stratiform of a Fluorine-Doped NiO Prism as an Enhanced Anode for Lithium-Ion Storage

Doping is regarded as a prominent strategy to optimize the crystal structure and composition of battery materials to withstand the anisotropic expansion induced by the repeated insertion and extraction of guest ions. The well-known knowledge and experience obtained from doping engineering predominate in cathode materials but have not been fully explored for anodes yet. Here, we propose the practical doping of fluorine ions into the host lattice of nickel oxide to unveil the correlation between the crystal structure and electrochemical properties. Multiple ion transmission pathways are created by the orderly two-dimensional nanosheets, and thus the stress/strain can be significantly relieved with trace fluorine doping, ensuring the mechanical integrity of the active particle and superior electrochemical properties. Density functional theory calculations manifest that the F doping in NiO could improve crystal structural stability, modulate the charge distribution, and enhance the conductivity, which promotes the performance of lithium-ion storage.

Synthesis and electrochemical performance of hollow-structured NiO + Ni nanofibers wrapped by graphene as anodes for Li-ion batteries

Hollow-structured NiO + Ni nanofibers wrapped by graphene were designed and successfully fabricated via a simple method. First, solid NiO + Ni nanofibers were prepared by electrospinning followed by calcination. Here, a portion of the metallic Ni was retained to improve the electrochemical performance of NiO by adjusting the calcination temperature. Next, the nanofibers were thoroughly mixed with different amounts of graphene and calcinated once more to form hollow-structured NiO + Ni nanofibers with an extremely high specific surface via the reaction between graphene and NiO on the nanofiber surface and subsequent migration of NiO into the nanofibers. Results showed that the obtained hollow-structured NiO + Ni electrode demonstrates optimal electrochemical performance when the graphene content is controlled to 3 wt%. The first cycle discharge/charge specific capacity of the electrode peaked (1596/1181 mAh · g^-1) at 100 mA · g^-1, with a coulombic efficiency of approximately 74% (60% for 0 wt% graphene, 65% for 1 wt% graphene, and 51% for 4 wt% graphene). It also presented excellent cycling stability after 100 cycles at 100 mA · g^-1on account of its high retained discharge specific capacity (251 mAh · g^-1for 0 wt% graphene, 385 mAh · g^-1for 1 wt% graphene, 741 mAh · g^-1for 3 wt% graphene, and 367 mAh · g^-1for 4 wt% graphene). Moreover, the synthesized electrode possessed outstanding rate capability owing to its large average discharge specific capacity of approximately 546 mAh · g^-1(45 mAh · g^-1for 0 wt% graphene, 256 mAh · g^-1for 1 wt% graphene, and 174 mAh · g^-1for 4 wt% graphene) from 100 mA · g^-1to 2000 mA · g^-1. The observed improvement in electrochemical performance could be attributed to the increase in active sites and decrease in charge transport distance in the hollow-structured NiO + Ni nanofibers. Excessive introduction of graphene caused a sharp loss in electrochemical performance due to the agglomeration of graphene sheets on the nanofiber surfaces.