Investigation On Strategy Of Dendrite-Free Lithium Metal Batteries And Theirs Cycling Stability

The surge in demand for portable electronics,electric vehicles,and grid storage,as well as the achievement of"dual carbon"goal,requires high energy density storage systems.In this regard,lithium metal batteries systems(LMBs)with high theoretical capacity(3860 m Ah/g)are generally considered to be able to meet the future demand for high energy density energy storage.However,the repeated volume changes of the lithium metal anode during cycling,the instability of the SEI,and the uncontrolled growth of lithium dendrites have hindered the practical application of LMBs.The grown lithium dendrites piercing the separator and further causing short circuits in the battery,which results in the thermal runaway,have attracted much attention.Therefore,except to seek a high specific energy lithium metal battery,the safety of the battery is also required to be overcome urgently.Based on the formation and growth process of lithium dendrites,two strategies are presented and designed in this thesis to realize the effective protection of lithium metal anodes upon operation.The formation of lithium dendrites is retarded by constructing three-dimensional conducting scaffolds(3D Zn O/CNTs/Cu),and the bad effects of uncontrolled growth of lithium dendrites is mitigated and eliminated by a modified PP/LTO/PP sandwich separator.Our proposed two strategies not only can inhibit the uncontrolled growth of lithium dendrites thus protect the lithium metal anode,also can greatly improve the electrochemical performance and safety of the battery.The main research conclusions of this thesis are listed as follows:1.A high-performance lithium metal composite anode based on a three-dimensional conductive network structure was preparaed successfully.The Zn O/C/CNTs materials were prepared by a traditional hydrothermal method,and the 3D Zn O/CNTs/Cu-based lithium metal matrixs with the ordered array structure were prepared by a freeze casting method.Meanwhile,the introduction of Zn O active sites within the scaffold can effectively improve the lithiophilicity,increase the nucleation sites for lithium deposition with a lower nucleation overpotential,and contribute to a uniform lithium ion deposition/exfoliation.The electrochemical test results show that the symmetric cells with the 3D Zn O/CNTs/Cu-based lithium metal exhibit a long cycle stability at current densities of 0.5 m A/cm~2,1 m A/cm~2,and 2 m A/cm~2,respectively.A reversible discharge capacity of 105 m Ah/g for LFP-based full cell can be delievered after 400 cycles at 1 C rate.Our results also reveal that the 3D Zn O/CNTs/Cu@Li composite anode can maintain the structural integrity during the cyclic process.This work suggests that the construction of 3D lithium-friendily composite anode is an effective strategy to inhibit the formation and growth of lithium dendrites,and extend the lifetime and safety of lithium metal batteries.2.LTO films were prepared by conventional scratch coating method and PP/LTO/PP sandwich separators were constructed together with Celgard 2400 separator.The porous structure of the LTO interlayer enhances the overall electrolyte wettability of the separator,which facilitates the rapid transport of lithium ions.While the LTO interlayer can not only act as a physical barrier,can also consume the lithium dendrites that contact the LTO of the separator,preventing them from penetrating the separator and improving the safety of the battery.Electrochemical performances show that Li/Li symmetric cells based on PP/LTO/PP composite separators can maintain a stable cycling with a very low polarization voltage for more than 1000 h.The PP/LTO/PP sandwich separator also contributes to the excellent cycle performance(600 cycles)and rate performance,and a high average Coulomb efficiency of 99.3%for Li/LFP full cell.The results show that the prepared PP/LTO/PP separator can significantly improve the stability of the interface between the lithium metal anode and the electrolyte and effectively stop the growth of lithium dendrites from penetrating the separator,which finally realize the long cycle life and high safety for lithium metal batteries.