Study On Li Metal Anode Protection Of Lithium Secondary Battery

Li metal anode is ideal for high performance secondary batteries due to its high theoretical capacity(3860 mAh·g-1)and low potential(-3.0405 V vs.S.H.E).However,uncontrolled lithium plating/striping and detrimental reactions with electrolyte during cycling renders lithium metal anode problems such as internal short circuit and lithium dendrite,causing safety and early failure issues to the batteries.In this study,three methods to modify and protect metallic lithium anode were designed and verified by different electrochemical performance tests.The results are as follows:(1)An artificial SEI film consisting of PVDF-HFP and nano-AlPO4 was designed to protect the metal lithium anode.The protective film has a thickness of 8.5 ?m and a Young's modulus of 1.6 Gpa,and has good mechanical properties,which can largely suppress the growth of lithium dendrites.With this nano composite layer,Li|LiFePO4 cells exhibit enhanced cycling stability and an extended lifespan of 400 cycles with respect to 90%capacity retention at 1C.Symmetrical Li|Li cells display a low over-potential of 375 mV and stable cycle over 750 at high current density of 3 mA·cm-2 with capacity density of 2 mAh·cm-2.(2)The PVDF-HFP/DMF/DMSO solution used to form an organic-inorganic gradient interface film on the surface of the metal lithium.The side close to the metal lithium is LiF with high surface energy and low diffusion barrier,which is called LiF-rich side;The upper surface of the gradient interfacial film is a PVDF-HFP gel film with good lithium ion conductivity and electrochemical stability,known as the PVDF-HFP-rich side.GIF-coated Li| GIF-coated Li symmetrical cells shows superior cycling over 600 h plating/stripping cycles under a high current density of 3 mA cm-2 with carbonate electrolyte,and the overall increased thickness of the symmetrical cells is only 24 ?m,while the LilLi symmetrical cells is thicker up to 59 ?m.(3)The zinc in the brass tape was dissolved to obtain a three-dimensional copper current collector,and then the surface of the three-dimensional copper current collector was galvanized by electroless zinc plating to obtain a lithiophilic three-dimensional porous Zn@Cu current collector.The three-dimensional porous Zn@Cu@Li with 3mAh·cm-2 lithium can stably cycle for 660 h at a current density of 0.5 mA·cm-2 in ether electrolyte and has a low polarization voltage of about 12 mV,which is far superior to 2D copper current collector and the 3D copper current collector reported in the literature.In summary,Li metal anode was protected from three different aspects:artificial SEI film,SEI film formed by in-situ on metal lithium,and lithiophilic three-dimensional current collector in this study.The performance of Li metal negative electrode made by these modification methods were all improved significantly.