| Rechargeable battery with Li metal as anode possessing high energy density has been considered as significant developing direction of high energy storage system.But during charge/discharge process of Li-metal battery,Li ions are easily deposited unevenly on the surface of Li electrode to form plenty of dendrites causing a short circuit inside the battery and even safety hazard.Thus it would be one of core scientific problems for preventing the growth of Li dendrites and improving cycling stability of Li-metal battery.Herein,main obstacles of Li anode are overcome and electrochemical performances of Li-metal battery are enhanced from the perspective of designing stable electrode interface and reasonable electrode structure,respectively.Main results are as follows:1.The PVDF polymer is coated on the surface of Li metal to obtain the Li@PVDF electrode which is subsequently tested in both symmetrical cell and full cell systems.Results show that the Li@PVDF electrode can inhibit the formation of Li dendrites and improve the cycle stability of batteries.In symmetrical battery system,the Li@PVDF electrode show a excellent cycling performance over 1400 h(700 cycles)at 0.5 mA cm-2 with 0.5 mAh cm-2,while the Li electrode displays very short cycling life with only for 400 h(200 cycles).SEM and AFM further prove that Li ions could uniformly be deposited on Li@PVDF electrode,however,a large amount of Li dendrites are easily formed on the surface of bare Li anode which is not protected by the PVDF film.In full cell system with LFP as cathode,the rate performance of the Li@PVDF electrode is significantly better than that of the Li electrode at large rates of 5 C and 10 C(1 C=0.25 mA cm-2).After 300 cycles at 2 C,the capacity retention of the Li@PVDF electrode is 89.8%,while it is only 82.7%for Li electrode.When the rate is increased to 4 C,the capacity retention of the Li@PVDF electrode is 80.0%after 500 cycles,which is larger than Li electrode with just 72.3%.2.Ag nanoparticles growing along Ni foam matrix could be realized by chemical reduction to get the Ag@Ni current collector and then the Li-Ag@Ni anode is fabricated when Li metal is deposited onto the Ag@Ni current collector.Firstly,charge/discharge behaviors of Ag@Ni and common Ni current collectors are compared in half cell system with Li metal as anode.Results illustrate that Ag@Ni current collector has better electrochemical performances.The nucleation overpotential is low when Li ions are deposited on the Ag@Ni current collector.At a small current of 0.02 mA cm-2 and 0.05 mA cm-2,the nucleation overpotential of Ag@Ni current collector approaches near zero and it is only 24.1 mV even under the high current density of 2 mA cm-2,While the nucleation overpotential is 66.4 mV for Ni current collector with 2 mA cm-2.In addition,the Ag@Ni current collector illustrates smaller polarization voltage and longer cycle life.Under 2 mA cm-2 and 1 mAh cm-2,the Ag@Ni current collector can stably circulate for more than 300 h(300 cycles),which is longer than Ni current collector with just 125 h(125 h).Besides,Ag@Ni current collector shows higher Coulomb efficiency than Ni current collector.At 5 mA cm-2 and 1 mAh cm-2,the Coulomb efficiency is only 87.3%of Ni current collector after 37 cycles.Ag@Ni current collector,however,remains a large Coulomb efficiency of 94.8%after 95 cycles.In full cell system with S as cathode,Li-Ag@Ni anode could present higher specific capacity and capacity retention.After cycling for 100 cycles under 0.2C(1 C=2.5 mA cm-2),the capacity retention of Li-Ag@Ni anode is 70.8%,while it is only 51.3%for Li foil anode.In addition,Li-Ag@Ni anode has better rate performance as well as higher reversible capacity.Finally,it could be directly seen from SEM that Li-Ag@Ni anode could keep its structure intact after cycling 350 cycles at 0.5 C.This work would open an new window for designing high-stable Li-metal anode being of significant for the enhancement of its long-life and safer performances. |
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