Study On Functionalized Carbon-based Materials In Nickel And Cobalt Sulfide Supercapacitors

In the current society,due to the strong rise of wearable smart electronic devices and the booming development of new energy electric vehicle industry,the demand for efficient,safe and lightweight energy storage and supply devices is increasingly urgent.Supercapacitor equipment with higher energy density than traditional capacitors and higher power density than secondary batteries has been a research focus in this field.At present,carbon materials are widely used for the conventional commercial supercapacitors,which can achieve the charge storage based on the mechanism of adsorption and desorption of electrolyte ions on the electrode surface.However,lower energy density(less than 10 Wh kg-1)is the shortcoming of capacitors based on this working mechanism.Thus,developing supercapacitor devices with higher energy density is crucial for the researchers and practitioners.Now some works have focused on seeking the new electrode active materials with higher specific capacity,which mainly enhanced the properties of supercapacitors by the methods of optimizing modification and balance matching methods,thus leading to the construction of high-performance supercapacitors with high power density,high energy density and long cycle life.Among them,designing a hybrid and asymmetric supercapacitors combined with the battery material and capacitor material would be the most extensive and effective approach.As mentioned above,most of the work is focused on the modification of electrode active materials.For achieving the high-performance capacitor devices,which usually involve a series of complex processes,various factors must be considered beside the nature of the active materials.So,the efficient and rapid electron transfer and ion diffusion reaction kinetics of the electrode must be ensured when constructing the nanostructures of the transition metal materials with high theoretical specific capacity.Therefore,it is necessary to effectively design and regulate the interface behavior between the whole electrode and the electrolytic liquid system,so as to improve the electrochemical performance of the capacitor at the interface dynamics level.The content and results are as follows:(1)Design of an intermediate carbon layer between bimetallic sulfide and carbon-based substrate for high-performance asymmetric supercapacitorsA N,P-doped intermediate carbon layer was constructed on the commercial CC(denoted as CC-NPC)that could serve as an excellent substrate for in situ assembling the bimetallic sulfide(BS)nanofibers,which can be used for the positive electrode(denoted as CC-NPC-BS)of the solid-state asymmetric supercapacitor device(CC-NPC-BS//AC).As a result,the introduction of N,P doped carbon layer greatly improves the hydrophilicity and chemical activity of carbon-based materials,which lays a foundation for the in-situ assembly of efficient nano-active materials.After growing well-ordered material,the strong coupling effect between the material and substrate not only makes the composite structure more stable but also promote the reaction kinetics more abundant,leading to the more efficient performance of active materials.Benefiting from the optimized structure,the as made CC-NPC-BS electrode can deliver a high specific capacitance value of 2250 F g-1 at a high charge-discharge current density of 20 A g'1,and the ASC device delivered a high energy density of 56.7 Wh kg-1 at the power density of 1.5 kW kg-1 and outstanding long cycle stability with 85%capacitance retention after 15000 cycles.(2)Design of a functionalized carbon cloth substrate for Nickel and Cobalt-based high-performance supercapacitorThe widely available and inexpensive cotton spinning cloth,which are made of cellulose,could be employed as the excellent carbon-based material after being carbonized.Herein,a functionalized N,P dual-doped porous carbon cloth(NPPCC)was prepared by carbonization of polyaniline covered on cotton spinning cloth in the attendance of phytic acid,which can directly act as a supporting substrate to in situ grow transition bimetallic sulfide(BS)nanofibers(the hybrid electrode denoted as NPPCC-BS).The outstanding hydrophilicity and electrochemical activity of NPPCC can achieve a robust growth of BS active materials,furthermore,the strong coupling effect between the carbon network and active materials makes the composite structure more stable and tunes the interface relationship.Benefiting from the structural characteristics,the whole reaction kinetics including transportation of ions and electrons and redox reactions processes were maximally enhanced.As a positive electrode of SCs,the NPPCC-BS hybrid electrode delivers a high specific capacitance of 1780 F g-1 at a current density of 50 A g-1.Furthermore,the as-assembled all-solid-state asymmetric supercapacitor(NPPCC-BS//AC)delivers a high energy density of 45.8Wh kg-1 at the power density of 15.7 kW kg-1 and an excellent long cycling stability of 88.6%retention after 15000 cycles.