Preparation And Performance Of Flexible Lithium-sulfur Full Batteries Based On N/o Co-doped Carbon Fabric

The rapid development of flexible wearable electronic products has increased the demand for high-performance flexible energy storage devices.Therefore,it is particularly important to develop flexible batteries which are light and thin,with good flexibility,high energy density,and good cycle stability.Lithium-sulfur battery belongs to a new generation of secondary battery energy storage technology,with high theoretical specific capacity(sulfur:1675 mAh g^-1;Lithium:3860 mAh g^-1),and low mass density(sulfur:2.07 gcm^-3;Lithium:0.534 gcm^-3),which has a broad application prospect in the field of flexible wearable energy storage.However,at present,Lithium-sulfur battery still faces serious problems such as polysulfide shuttle effect,huge electrode volume expansion,random deposition of insulating Lithium sulfide and dendrite growth of Lithium metal anode,which lead to poor coulombic efficiency and cycle stability of batteries.In addition,the flexibility of Lithium-sulfur battery is poor in various mechanical deformation processes such as bending and curling,and the sulfur cathode is prone to fall off active substances,while the Lithium metal anode is prone to fatigue fracture.Therefore,in order to obtain high performance flexible Lithium-sulfur batteries,the cyclic stability and flexibility of both the sulfur cathode and the Lithium metal anode must be solved.In response to the above problems,we prepared a nitrogen-oxygen co-doped carbon fabric（NOCF）with good affinity for both polysulfide and Lithium,and used it as the current collector of the sulfur cathode and the Lithium metal anode.Incorporating natural water-soluble sericin protein（SP）as the sulfur cathode binder,a sulfur cathode（SP/S/NOCF）and a composite Lithium metal anode（Li/NOCF）with excellent flexibility and good cycle performance are obtained.The Lithium-sulfur half battery composed of SP/S/NOCF cathode and Lithium foil has a areal capacity of 5.4 mAh cm^-2when the sulfur loading is 6 mg cm^-2,and the capacity retention rate is above 85%after cycling 100 times.The average coulombic efficiency of the Li/NOCF composite anode is up to 99.0%at 1 mA cm^-2for 6 mAh cm^-2of Li.And the symmetric battery can cycle stably for more than 1200 h at 1 mA cm^-2.When the current increased to 2 mA cm^-2,it could still maintain stable cycle for more than 500 h.By matching SP/S/NOCF cathode with Li/NOCF anode,the energy density of the coin Lithium-sulfur full battery（cathode+anode+seperator）is up to 694.1Wh kg^-1(510.8Wh L^-1).The final flexible Lithium-sulfur battery（SP/S/NOCF//Li/NOCF）can still cycle stably for more than 150 times after 6000 flexing cycles at a small radius of 5 mm,and it can also charge and discharge normally during in-situ dynamic bending test（r=5 mm,2200 times bending）.In this paper,SEM,TEM,XPS,XRD,BET,Raman and other characterization methods were used to analyze the morphology,structure and element composition of NOCF.Galvanostatic charge/discharge test and isobarically discharge experiments were used to explore the mechanism of NOCF’s adsorption of polysulfide and inhibition of Lithium dendrite.In addition,the practicability of the flexible full Lithium-sulfur battery was verified by a series of flexible bending tests.NOCF has a good affinity for both polysulfide and Lithium due to its nitrogen-oxygen co-doped structure,which can be used to inhibit the"shuttle effect"of polysulfide and the growth of Lithium dendrite.This can provide a theoretical basis and reference for the future design of high performance super soft Lithium-sulfur batteries.