The Design And Research On Silicon-based Lithium Ion Oxygen Batteries

The environmental issue and the energy crisis have limited the steps of human beings heading to the sustainable development.Developing the green energy has thus become a common view for the contemporary society.The usage of green energy needs high performance energy storage systems.Since 1990's,lithium ion batteries(LIBs)have achieved a huge success in portable electric devices.However,with the intrinsic limitation of the active materials used,LIBs fail to satisfy the large electric equipment.Recently,researchers have paid their attention to lithium oxygen(Li-O2)batteries.Li-O2 batteries take advantage of continuous oxygen from the external atmosphere and lithium anode with the highest specific capacity.However,the lithium metal suffers from the dendrite growth and low Coulombic efficiency.Researchers come up with lithium ion oxygen(Li-ion O2)batteries by replacing the lithium anode with the alloy-based anode.Silicon materials are considered to be a potential alternative for its high specific capacity and low operating potential.In this thesis,we design and construct Si-based Li-ion O2 batteries.With the help of characterization and discharge-charge tests,we investigate the electrochemical properties and reaction process of the batteries.We firstly synthesized two multi-walled carbon nanotube(MWCNT)based composite materials as cathode materials for Li-ion O2 batteries.In the platinum decorated MWCNTs(Pt-MWCNTs)material,Pt particles are uniformly decorated on the MWCNTs.In the core-shell ruthenium dioxide MWCNTs(RuO2-MWCNTs)material,crystalline RuO2 covers the surface of MWCNTs and form a core shell structure.The Li-O2 battery with Pt-MWCNTs cathode can run stably for 100 cycles.RuO2-MWCNTs can efficiently reduce the charge overpotential and improve the cycle stability.We characterized the Pt-MWCNTs cathodes after discharge and recharge,and found the formation and decomposition of crystalline Li2O2 in the cathode.Considering the absence of lithium in the silicon electrode,we proposed to use high energy ball milling method to synthesize the Li-Si alloy.The Li-Si alloy has a composition of Li21Sis,and the particle size ranges from 1 ?m to 5 ?m.Theelectrochemical test shows that Li-Si alloy has a delithiation capacity of 1118.0 mAh·g-1.And it has a capacity retention of 571.1 mAh·g-1 after 50 cycles.A Li-ion O2 battery is then constructed with Pt-MWCNTs cathode and Li-Si alloy anode.And the battery can be discharged and charged at a current of 500 mA·g-1 for 80 cycles.We also investigate cycle stability of Li-ion O2 batteries with different anode/cathode mass ratio.By comparing the Li-Si anodes before and after cycling,we found the amorphization of Li-Si alloy and the presence of LiOH and undissolved ether species during cycling.These by-products accumulate in the anode and lead to the battery failure.We design and construct a flexible packaging battery with a pre-adopted lithium source.The pre-adopted lithium source is used to lithiate silicon anode before the Li-ion O2 battery function.We used alginate sodium as binder to prepare silicon anode.The silicon anode has a 1st discharge capacity of 3087.8 mAh·g-1,and a capacity retention of 1500.2 mAh·g-1 after 200 cycles at a cycle rate of 0.25 C.In the flexible packaging battery,the silicon anode is partially lithiated by continuous discharge and rest.The discharge product Li-Si alloy in this battery system has the composition of Li21Si8.And the Li-ion O2 has a discharge capacity of 343.1 mAh·g-1,with a Coulombic efficiency of 100%.This strategy can not only realize the electrochemical lithiation of silicon anode,but also eliminate the complicated procedures during manufacture.Our primary research focuses on the design and construction of Li-ion O2 batteries.This will provide new ideas for the structure design and property optimization of Li-ion O2 batteries in the future.