Optimization Of Carbon And Its Composite Materials To Enhance The Specific Capacitance And Energy Density Of Supercapacitor Based "Structural Engineering"

Supercapacitors（SCs）with fast charging and discharging capacity play an important role in the fields of renewable energy storage and conversion,new energy-powered transportation,and portable wearable devices.Although SCs have great potential in an applicable scene requiring high power,poor energy density is still limiting the further development of SCs in future energy systems.Therefore,it is necessary to apply the concept of"structural engineering"to optimize and design the electrode materials,synthesize the electrode materials that form electric double layers efficiently and have Faraday active sites to improve the energy density of SC.In this paper,adopting the"pores engineering"strategy for carbon combining large specific surface area and adjustable structure or properties,the nitrogen-doped hierarchical porous carbon with tuned micro/mesopores and packing density was prepared through activating the similar structure and good compatibility dual-precursors,calcium gluconate（CG）and chitosan（CS）.The typical sample CG1CS2-K shows a relatively high density of 0.83 g cm^–3,plentiful surface heteroatoms（14.1 at%for O and 3.3 at%for N）.What’s more,CG1CS2-K based electrodes represent excellent gravimetric capacitance of 386 F g^-1and volumetric capacitance of 320 F cm^-3.In two-electrode system,it exhibits a high energy density of 16.23Wh kg^-1/13.47 Wh L^–1,and assembled all solid-state button supercapacitors easily power 13red LEDs,proving that the material has practical application value.To overcome the low rate performance,poor conductivity,and weak cyclic stability of asymmetric supercapacitor（ASC）anode material,in this work,layered Ni/Co hydroxide@carbon composites were prepared by coprecipitation using calcium gluconate derived mesoporous carbon with rod shape as substrate and the effect of Ni/Co ratio on electrochemical properties was investigated.The experimental results show that the high specific surface area and pore volume of the substrate provide a wide space for Ni Co（OH）x to disperse and grow,which not only improves the mass transfer between Ni Co（OH）x and electrolyte but also increases the conductivity.The rate performance and specific capacity of the best composite material Ni Co1-1@CG-700 were enhanced remarkably.Then,ASC was assembled using porous carbon CG1CS2-K as the cathode and composite material Ni Co1-1@CG-700 as the positive electrode.The voltage window of ASC can be extended to 1.6 V ensuring the performance is completely released.The energy density significantly increased to54.2 Wh kg^–1,even in higher current density(20 A g^–1),it remained at 38.0 Wh kg^–1(～2.2 W kg^–1).Meanwhile,the specific capacitance remains 82%after 5000 cycles.Finally,two ASCs in series drive an electronic watch with a rated voltage of 3.0 V and light 18 LEDs proving the practicability.