Preparation Of Metal-Doped Porous Carbon From PDA And Its Application In Lithium-Sulfur Batteries

With the development of society,portable electronic products and new energy vehicles are rapidly popularized,which puts forward higher requirements on the performance of secondary batteries while making people's lives easier.In order to meet the above needs,lithium-sulfur batteries(Li-S)with high theoretical specific capacity and specific energy have received extensive attention from scholars.However,some problems in the positive electrode of lithium-sulfur battery make the actual specific capacity and the theoretical specific capacity differ greatly in practical application,such as the harmful shuttle of polysulfide intermediates,complex heterogeneous sulfur redox reactions,and the uncontrollable precipitation of discharge products(Li₂S₂ and Li S₂),poor cycle stability and rate performance,greatly limit its practical application.In order to solve the above problems,this paper uses porous carbon as the starting point,and successfully synthesizes polydopamine(PDA)nanoparticles by self-polymerization at the oil-liquid interface,and uses this as the precursor of carbon materials for carbonization,and prepare the carbon nanocomposite material from PDA doped with different metals,to solve the current problems of lithium-sulfur batteries and obtain high-performance batteries.First,this article successfully prepared PDA nanoparticles with a diameter of about 200 nm.After carbonization,porous structured carbon nanospheres(NSC)were prepared.The prepared carbon nanospheres were loaded with sulfur to obtain a carbon/sulfur composite material for use in lithium-sulfur batteries.The utilization rate of sulfur and cycle stability were improved significantly.Because NSC has a large specific surface area,continuous electron and ion transport paths,NSC is used as the carrier of S,so that the NSC/S electrode has good energy storage capacity and extremely high electrochemical stability.Therefore,Li-S with NSC/S as the positive electrode has a high initial capacity of 846 m Ah·g^-1(0.2 C),stable cycles for 200 times,a capacity decay rate of 0.18%per cycle,and the subsequent capacity retention rate is 75.54%after a long cycle of300 times at a current density of 1.0 C.It shows that the material significantly improves the sulfur utilization rate and the cycle stability of the battery,and is an active material for lithium-sulfur batteries with great application potential.On the basis of the PDA nanospheres,different proportions of cobalt were doped into the PDA by the post-doping method,and the Co metal/carbon composite materials with different doping amounts were obtained after high-temperature carbonization(NSC-Co_x).The results show that the material has a large specific surface area and mesoporous structure.The cobalt element mainly exists as elemental cobalt in the doped NSC nanospheres.Co metal doping can increase the strength of the carbon skeleton.As the amount of metal doping increases,the conductivity of the battery cathode increases.After sulfur is loaded,it is used in lithium-sulfur batteries.When x=4,it has a high sulfur utilization rate——the initial capacity is 1109 m Ah·g^-1 at a current density of 0.2 C,excellent rate performance and long-cycle stability(300 cycles at 1.0 C,of which each cycle is 0.06%).This work provides a simple solution for accelerating the reversible conversion of lithium polysulfide into high-performance Li-S batteries for high-load single metals.In addition,this article also doped different proportions of iron into PDA,and after high-temperature carbonization,iron/carbon composites with different doping amounts were obtained.The results show that the material also has a large specific surface area and mesoporous structure,which can achieve high-quality sulfur loading.The iron element mainly exists in the form of iron carbide in the doped composite nanospheres.On the one hand,iron carbide can adsorb polysulfide ions,and on the other hand,it can accelerate the conversion of polysulfide,thereby increasing the charge and discharge rate of lithium-sulfur batteries.NSC-Fe_x is loaded with sulfur for lithium-sulfur batteries,when x=4,the reversible capacity of the NSC-Fe₄/S electrode at 0.2 C is 1277m Ah·g^-1,and the initial capacity at 1.0 C is 1277 m Ah·g^-1,the average attenuation is 0.04%after300 cycles.