Advanced Cathode And Anode Materials For Alkali Metal Sulfur Batteries

Room-temperature alkali metal sulfur batteries?Li-S and Na-S?are promising candidates of next generation energy storage due to the high theoretical capacity of S cathode(1672 mAh g^-2)and alkali metal anode(Li:3861 mAh g^-1;Na:1166 mAh g^-1;K:685 mAh g^-1).But unfortunately they suffer from serious cycling problems rooted in their polysulfide intermediates and the safety issues caused by the unstable cycling of alkali metal metal anode.Herein,we designed both S cathode and alkali metal anodes to enhance their cycling performance respectively.Then we couple alkali metal anodes with different cathode materials including the designed S cathode to demonstrate the practical implementation value of our strategies.In the first study,we revisit the unique sulfiphilic nature of metallic Cu.Upon the exposure to polysulfide in aqueous or aprotic solution,the surface sulfidization rapidly took place,resulting in the formation of Cu₂S nanoflake arrays with tunable texture and thickness.When sulfidized Cu foam is used as the sulfur-equivalent cathode,it enables high-performance Li-S and Na-S batteries at room temperature.Specific capacities up to¹200 mAh g^-1for Li-S and⁴00 mAh g^-1for Na-S are achieved when normalized to the amount of equivalent sulfur.The excellent performance can be readily sustained for>1000 cycles.In the second work,we report an universal and straightforward strategy to improve the plating/stipping performances of Li,Na and K metal anodes.When covered with a thin piece of commercial carbon paper as the protection layer on their surfaces,the anodes all exhibit significantly enhanced overpotentials and plating/stipping stability?up to⁴000 cycles for Li,¹200 cycles for Na and³000 cycles for K?within carbonate or ether electrolyte and even a large current density of 5 mA cm^-2.Proof-of-concept lithium metal batteries are assembled by using the protected Li metal anode couple with Li₄Ti₅O₁₆?LTO?,sodium metal batteries are assembled by using the protected Na metal anode couple with Na₃V₂?PO₄?₃?NVP?cathode or the sulfidized Cu foam in the first work,and they all demonstrate large areal capacity and impressive cycling life.Given the effectiveness,scalability and low cost of carbon paper,we believe that our strategy holds great promise for practical application.