Polymer Encapsulation To Synthesize Atomic Electrocatalyst And The Application Of Its Modified Separator In Li-S Batteries

Lithium-sulfur batteries have become an attractive new generation of energy storage batteries because of their theoretical specific capacity up to 1675 mA h/g,abundant raw material reserves,low cost,non-toxic and other advantages.However,the shuttle of polysulfide in electrolyte and the slow reaction kinetics during charge and discharge seriously restrict the practical application of lithium-sulfur batteries.As an important part of the battery,separator plays an important role in the electrochemical performance of the battery.The polymer separator with micropores can separate the positive and negative electrodes to avoid short circuit.However,the pores of the separator are too large to block the passage of polysulfides.We proposed a polymer encapsulation strategy to prepare metal atoms and nitrogen co-doped hollow carbon sphere electrocatalytic material as a coating for lithium-sulfur battery separator,and investigated its catalytic effect on polysulfide conversion and its influence on electrical properties.The main work is as follows:(1)Aiming at the problem that metal atoms are difficult to uniformly disperse,a polymer encapsulation method was designed in this paper.Based on the non-covalent interaction between dopamine and metal salts,atomic cobalt and nitrogen co-doped hollow carbon spheres(A Co-NHC)material was successfully prepared and used to modify the separator,and its influence on the electrical properties of lithium-sulfur batteries was studied.The results show that the polymer encapsulation method is better than the common impregnation method to prevent the agglomeration of metal atoms and form the monatomic metal catalyst.A Co-NHC material can effectively accelerate the transformation of poly sulfide and inhibit the polysulfide shuttle effect.The battery based on A Co-NHC/PP separator can reach the specific capacity of 1084.9 mA h/g at 1 C constant current discharge.After 100 charges and discharges,the lithium-sulfur battery still has a specific capacity of 837.7 mA h/g,and its electrical performance is better than that of commercial PP separator.(2)Atomic iron and nitrogen co-doped hollow carbon spheres(A FeNHC)were synthesized by polymer encapsulation method based on the covalent interaction between dopamine and metal salts and was used as the excellent multifunctional separator coating for lithium sulfur batteries.The effect of the coating on the electrical properties was studied.The results show that the synergistic effect of A Fe-NHC material on polysulfide adsorption and electrocatalysis accelerates the conversion of polysulfide,and effectively limits the shuttle effect.The battery based on A Fe-NHC separator has excellent electrical performance,and the specific capacity of the battery is up to 1079.4 mA h/g at a current density of 1 C.After 100 times of constant current charge and discharge,the remaining specific capacity is 858.4 mA h/g.The specific capacity of 823.7 mA h/g can be maintained even at 4 C constant current discharge at high current density.