Construction Of Zirconium Based Fluorine-rich Interfacial Layer And Two Dimensional Lithium Conducting Solid Acid For Suppressing Lithium Dendrites

Lithium metal anode is considered to be the most ideal anode material for next-generation lithium batteries because of its high theoretical specific capacity(3860m Ah g^-1)and ultra-low redox potential（-3.04 vs SHE）.Lithium metal anode can also be matched with conversion reaction cathode materials（such as sulfur cathode,oxygen cathode）to promote the development of high energy density battery system.However,the dendrite problem of lithium metal anode can lead to a sharp decline in battery performance.Therefore,preventing the growth of lithium dendrite is the key to the practical application of lithium metal anode.Aiming at the problem of lithium metal anode dendrites growth,this paper mainly designs two strategies to inhibit the growth of lithium dendrites.The specific studies are as follows:（1）A simple sol-gel method was developed to prepare porous zirconium oxyfluoride（Zr-O-F）whose surface is modified by organics,and use it to construct a fluorine-rich modified layer on the surface of lithium metal.Using ethylene glycol as solvent,Zr O（NO₃）₂·x H₂O as zirconium source and HF solution as fluorinating agent,the xerogel was treated at 120℃to obtain Zr-O-F compound with mesoporous morphology,XPS showed that the surface of Zr-O-F particles was rich in organic modification such as C and N,BET test showed that its specific surface area was 45.9 m~2/g.A fluorine-rich interfacial protective layer is constructed by the reaction of porous Zr-O-F compounds with the surface of lithium slice.The protective layer is located under the plated metal lithium after battery is cycled,which can effectively adjust the plating/stripping behavior of metal lithium,and regulate the composition of SEI layer,increase the content of Li F in SEI layer,synergizes with the SEI layer located above the lithium metal,enabling the lithium metal anode to achieve better cycling performance.At the current density of 1m A cm^-2 and the area capacity of 2 m Ah cm^-2,the lithium symmetric battery composed of lithium metal anode with Zr-O-F protective layer can cycle for up to 2000 h and exhibits excellent rate performance.The battery assembled with the lithium metal anode with a protective layer and the NCM811 cathode also showed good cycle performance,the capacity retention rate was still 78%after 400 cycles at 1C rate.（2）The two-dimensional solid acidα-zirconium phosphate was transformed into nanosheets with high conductivity on the surface by the"grafting-oxidation-exchange"method.Then,it was used to modify the PP（polypropylene）separator,effective lithium dendrite suppression was achieved by regulating the plating/stripping behavior of lithium ions.ZrP-SH was obtained by graftingα-zirconium phosphate nanosheets which were exfoliated into few-layer structure,and then the end group were oxidized to obtain ZrP-SO₃H,ZrP-SLi was synthesized after cation exchange.ZrP-SLi retains the high temperature stability and layered structure ofα-zirconium phosphate,which forms an effective flame retardant barrier after being deposited on PP separator,so the separator can resist thermal shock,improve battery safety.The mechanical properties of ZrP-SLi can effectively suppress lithium dendrites.Benefiting from the adsorption of TFSI^-by the nanosheet structure in ZrP-SLi and the rapid coordination and dissociation of-SO₃^-on the side chain with Li ions,PP separator modified by ZrP-SLi（ZrP-SLi-PP）effectively increased the number of lithium ion transference number t _Li+near the lithium anode interface and improved the kinetics of lithium ion migration.The Li symmetric battery with ZrP-SLi-PP separator can still cycle 2500 hours even at a current density of 5 m A cm^-2,an area capacity of 2.5 m Ah cm^-2 and a current density of 10 m A cm^-2,an area capacity of 1 m Ah cm^-2,showing good adaptability at large current density and area capacity,and the surface of the lithium anode after cycle is smooth and dense.The Li/NCM811 battery with ZrP-SLi-PP separator still has 80%capacity retention rate even after 650 cycles at 1C rate.