Preparation Of Porous Carbon And Its Application In Lithium-Sulfur Batteries

With the development of modern society, the problem of energy consumption and environmental put forward a great challenge for our society. Therefore, development of rechargeable lithium batteries with high safety, high energy density and high specific capacity is a necessary part of modern society development. In recent years, rechargeable Li-S batteries have gained great attraction, because of their high theoretical energy density of 2600 Wh/kg, high theoretical specific capacity (1675 mAh/g). Moreover, sulfur is naturally abundant, inexpensive and nontoxic contributing to its advantages. Porous carbon materials with excellent electric conductivity, large surface area and pore volume and strong adsorption ability as a carbon matrix were applied to Li-S batteries, and demonstrated improve the discharge capacity and the cycle life of Li-S batteries.In this work, we report variety of simple, low-cost and high yield strategy for the preparation of porous carbon materials for Li-S batteries.The main contents and results are as following:(1) The porous carbon nanosheets (PCNS) with a high surface area were obtained by carbonizing corncob waste material and followed by activation by potassium hydroxide. The PCNS are used as the conducting matrix for sulfur to form sulfur/porous carbon nanosheets (S/PCNS) composites, which are applied as cathodes for lithium-sulfur (Li-S) batteries. The S/PCNS composites exhibit a high initial discharge capacity of about 1600 mAh/g and maintain a reversible capacity of 554 mAh/g after 50 cycles. The superior performance is attributed to the highly porous structure of two-dimensional carbon nanosheets that not only enables stable and continue pathway for rapid electron and ion transportation, but also restrain soluble polysulfides and suppress the "shuttle effect". The large surface area and unique sheet-like two-dimensional structure of PCNS also leads to a high utilization of sulfur.(2) A low cost and high production activated carbon produced from finger citron were used as electrodes for Li-S batteries. We successfully prepared finger-citron-based activated carbon (FAC) by carbonizing from finger citron residues and followed by activation by potassium hydroxide. The porous carbon FAC with high surface area of 3157 m2/g and large pore volume of 2.162 cm3/g and partial lamellar structure. The high specific surface area of the meso/microporous carbon facilitate the cathode materials infiltration of electrolyte, which give rise to high initial sulfur utilization and rate capability. The S/FAC with 52% sulfur composites at 0.2 C rate exhibit initial capacities of 1311 mAh/g. The composite still retains a capacity of 818 mAh/g and 687 mAh/g, after 50 and 100 cycles, respectively.(3) A simple method for the preparation of mesoporous carbon with high surface area (2166 m2/g) and very large pore volume (4.09 cm3/g) by the direct carbonization of adipic acid and zinc powder mixture without further chemical/physical activation process. The mesoporous carbon is composed of nanosheets with plenty of nanocapsules-like pores around 15 nm, exhibiting a hierarchically assembled flower-like structure. These hierarchical porous carbon nanosheets (PCNS) are used as supporter for sulfur to form a homogeneous composite (S/PCNS) though a conventional heat treatment process. Excellent electrochemical performance is achieved for this S/PCNS as cathode of Li-S battery. The S/PCNS composite with 62 wt% sulfur delivers a high initial discharge capacity of about 1384 mAh/g and maintains a reversible capacity 657 mAh/g after 100 cycles at 0.2C rate.