Research On Controllable Preparation And Structure-effect Relationship Of Composite Lithium Metal Anode

The development of science and technology has triggered the continuous improvement of people’s living standards,and the demand for energy has also increased dramatically.On the contrary,the wide-used non-renewable energy sources including natural gas and oil has been almost exhausted.Therefore,it is important to find new and clean energy sources.Among them,the new energy storage equipment mainly based on lithium-ion batteries has changed the mode of communication and transportation of modern life.Especially high-energy-density lithium metal battery based on lithium netal anode that has the highest theoretical specific capacity(3860 m Ah cm^-2)and the lowest electrochemical potential（-3.04V vs.standard hydrogen electrode）has been widely researched.But the reason why that have not been commercialized so far is that the high reactivity between the lithium metal and electrolyte leading to the consumption of lithium and electrolyte.At the same time,it causes huge volume expansion and the growth of dendrite during the cycling process,which resulting in SEI film of electron interface is unstable and leading to low coulombic efficiency and poor cycle performance,even bringing about battery explosion.So far,there are many strategies have been proposed to successfully suppress the growth of dendrites and improvement the cycle performance of the lithium batteries,which mainly include electrode interface and structural optimization.However,with the extension of cycling time,the use of only one method is far from being able to suppress dendrites effectively,and few strategies based on combine the advantages of two strategies are utilized to improve the lithium metal battery’s Performance.Therefore,starting from the electrode interface and structural issues,this paper carried out the following research contents:1.The strategy of molten metal lithium infused a three-dimensional（3D）porous framework to construct 3D composite lithium metal anode（LMA）is effective for solving the relative volume change of LMA during lithium plating/stripping.However,few people pay attention to the controllable regulation of the structure and interface of 3D composite LMA simultaneously.In this study,a 3D composite LMA was prepared by infused molten metallic lithium into carbon fiber（CF）paper modified with nanoporous gold（NPG）,and Au was converted into Au Li₃in the process.Then,a simple and effective pre-stripping（PS）technology was used to achieve a controllable strategy for the structure and interface.As a result,the surface of the 3D composite LMA originally was exposed to a part of the skeleton,which greatly improving the electrochemical performance.Based on this,in a commercial carbonate-based electrolyte,Li|Li symmetrical battery based on the composite anode showed a low overpotential of 111 m V after cycling for 1800h at a current density of 0.5 m A cm^-2.In addition,the full cell based on composite anode and Li Fe PO₄（LFP）cathode showed a high capacity retention rate of 96.1%and Coulomb efficiency of 99.2%at 5C after 1000 cycles;The full cell based on composite anode and sulfide polyacrylonitrile（SPAN）cathode showed a high capacity retention rate of 70.6%and Coulomb efficiency of 99.8%at 2C after 1000cycles.2.A hollow carbon fiber loaded with lithiophilic phase Li₃Sb（Li₃Sb-HCF）was demonstrated by electrospinning-carbonization technology.Meanwhile,by controlling the cut-off voltage（0～0.3V）,the Li₃Sb phase was kept unchanged during the cycle and Sb was avoided pulverization caused by excessive volume change（175%vs.Li）during Li plating/stripping.Based on the hollow nano-carbon fiber structure,the absorption of the liquid electrolyte can be greatly improved by capillary phenomenon,which shortening Li-ion diffusion path,which beneficial to more uniform plating/stripping behavior.More importantly,it is a simple and fast method to construct a 3D carbon fiber network with high electron conductivity and Li₃Sb with high ion conductivity,so as to build a ion-electron mixed conductor（MIEC）current collector,which accelerate Li⁺and electron transmission dynamics and reduce interface impedance,reaching a dendrite-free morphology.Specifically,at a high rate of up to 10 m Ah cm^-2,a coulombic efficiency of 97.3%can be achieved up to160 cycles.At the same time,the Li|Li symmetrical cell based Li₃Sb-HCF of pre-plating with 3 m A cm^-2also achieved cycle over 1900h at ultra-low overpotential.The unique 3D composite lithium metal anode composed of high ion conductivity Li₃Sb and high electron conductivity hollow carbon fiber provides a new research path for the development of high-rate and long-cycle stable lithium metal batteries.