| Lithium-ion battery（LIB）is widely used in wearable equipments,portable electronic devices,electric vehicles and hybrid vehicles,because of its high energy density,high working voltage,low self-discharge rate,long cycle life and no memory effect.At present,commercial lithium-ion batteries still use graphite as anode materials.The low capacity of graphite(372 m Ah g-1)cannot meet the needs for higher energy density and higher power density.It is urgent to develop new anode materials with higher specific capacity and lower discharge potential.Alloying and conversion reaction materials can store more Li+by alloying or redox reaction showing a significantly higher capacity than intercalation materials（like graphite）.However,huge volume change in the charge/discharge cycles may destroy the electrode structure,resulting weak cyclability and rate performance,which makes them difficult to be applied in practice.Herein,we combine conversion and alloying materials to buffer the volume change,decrease the operating voltage and utilize their high capacity.In this work,we investigate core-shell Sn@Mo S2 as conversion/alloying materials,focusing on the in-situ interfacial configurations,lithium storage performance and working mechanism.The main contents are as follows:1.The core-shell Sn@Mo S2/CNF with excellent cycle stability,high capacity retention and high rate performance was synthesized via electrospinning-pyrolysis processes.The synergistic effect of Sn and Mo S2 was realized by combining the mechanism of conversion and alloying reaction.Sn improves the conductivity of Mo S2 while the Mo/Li2S atomic matrix derived from Mo S2 lithiation buffers the huge volume change of Sn.Meanwhile,Li2S released from the conversion of Mo S2 drives the further oxidation of partial Sn to Sn S,causing electrochemical melting to the Sn nanoparticles,which increased its cyclability.Mo,the lithiation product of Mo S2in the subsequent cycles,shows strong Sn affinity to effectively inhibit the coarsening of ultrafine Sn grains,enabling the good retention of lithiation/delithiation.The evolution of solid–electrolyte interphase（SEI）structure was systematically characterized.We found that there is a partially reversible redox reaction on the SEI of Sn@Mo S2/CNF electrode,which contributes to the additional Li+storage capacity in the high potential range.This work will inspire the exploitation of electrode materials and the in-depth understanding on their working states and mechanism.2.We further investigate the preparation and Li-storage mechanism of Sb/Mo C/CNF self-supported electrodes.PAN fiber loaded with Sb and Mo source was prepared by electrospinning,and was further converted into flexible Sb/Mo C/CNF monolith by pyrolysizing at high temperature.It is found that the Sb/Mo C/CNF-700 obtained after annealing at 700℃for one hour shows best cyclability and rate performance.Flexible Sb/Mo C/CNF-700 is further used as the model for further studying the effect of O2 plasma etching on lithium storage performance.After etching by O2 plasma,the specific capacity of the Sb/Mo C/CNF-700 is improved,however,their cyclability and rate performance are unfortunately reduced.Indicated by the kinetic analysis,Li+storage in the etched Sb/Mo C/CNF-700 electrodes（Sb/Mo C/CNF-700-1min,Sb/Mo C/CNF-700-2min）is mainly contributed by diffusion-limited process,while initial Sb/Mo C/CNF-700 is mainly contributed by pseudocapacitive intercalation.The changes of the reaction dynamics make impacts on the electrode cyclability and rate performance. |
PDF Full Text Request