The Preparation And Electrochemical Performance Of Graphene-modified Freestanding Ni-based Nanostructures As Anode For Lithium Ion Batteries

Conversion type anode materials（transition metal oxides,sulfides,phosphides,nitrides,etc.）for lithium ion batteries have attracted much attention owing to their low cost,natural abundance and high theoretical capacity.However,they suffer from low electronic conductivity and large volume variation upon cycling,resulting in capacity attenuation and unsatisfactory cyclability.In this paper,we try to design high performance Ni based compounds（nickel oxide,nickel sulfide and nickel phosphide）as anode for lithium ion batteries.Three-dimensional porous freestanding architecture design and graphene decoration strategies were used to improve the performance these electrodes.The main research contents are as follows:1.The growth of Ni O on graphene modified nickel foamNi O nanoflakes were directly grown on graphene modified nickel foam（Ni O-G-Ni）via electrochemical corrosion with subsequent annealing.The Ni O-G-Ni electrode shows high pseudocapacitive charge storage with capacitive contribution of 78%at 0.1 m V s^-1.The Ni O-G-Ni electrode delivers initial discharge/charge capacity of 936/734 mAh g^-1 at a current density of 125 m A g^-1,showing discharge capacity of 732/722 mAh g^-1 after 150cycles.2.The growth of nickel sulfides on graphene modified nickel foam（1）The preparation of Ni₃S₂ electrode.Ni₃S₂ nanoflakes were directly grown on graphene modified nickel foam（Ni₃S₂-G-Ni）via hydrothermal reaction.The Ni₃S₂-G-Ni electrode delivers initial discharge/charge capacity of 565/502 mAh g^-1 at 1C,showing discharge capacity of 398 mAh g^-1 after 100 cycles;At a high current density of 9C,the Ni₃S₂-G-Ni electrode delivers initial discharge/charge capacity of 787/484 mAh g^-1,showing discharge capacity of 320 mAh g^-1 after 1000 cycles.（2）The preparation of Ni_xS_y.Ni_xS_y microflakes were directly grown on graphene modified nickel foam（Ni_xS_y-G-Ni）via dry sulfuration approach.In the Ni_xS_y-G-Ni,Ni_xS_yconsists of Ni S,Ni S_1.03,and Ni₉S₈.The Ni_xS_y-G-Ni electrode delivers initial discharge/charge capacity of 838/702 mAh g^-1 at 0.1C,showing discharging capacity of569 mAh g^-1 after 100 cycles.At a high current density of 3C,the Ni₃S₂-G-Ni electrode delivers initial discharge/charge capacity of 512/454 mAh g^-1,showing discharge capacity of 282 mAh g^-1 after 1000 cycles.3.The growth of Ni₂P on graphene modified nickel foamNi₂P nanoflakes were directly grown on graphene modified nickel foam（Ni₂P-G-Ni）via phosphating method.The Ni₂P-G-Ni electrode delivers initial discharge/charge capacity of 1196/688 mAh g^-1 at 0.8C,showing discharge capacity of 638 mAh g^-1 after350 cycles.At a high current density of 2C,the Ni₂P-G-Ni electrode delivers initial discharge/charge capacity of 1092/416 mAh g^-1,showing discharge capacity of 336 mAh g^-1 after 500 cycles.