Preparation And Electrochemical Properties Of Cathode Materials For Lithium-Sulfur Battery

For the widespread application of devices such as mobile devices, electrical energy storage and the inescapable of exhaustion of fossil fuels, it is critical to develop high-energy-density recharge batteries. Among available electrical energy storage systems, rechargeable lithium-ion batteries play an important role in portable electronics such as mobile phone, laptops and many other aspects. However, lithium-ion batteries are not capable of meeting energy storage requirements such as portable electronics, transportation and so on. Lithium-sulfur battery has been investigated as a viable and more attracted candidate to the next generation lithium ion battery due to its specific energy density (2600 Wh kg-1) and high theoretical capacity (1675 mAh g-1). Besides, sulfur is abundance, low cost, no-toxic and environment friendliness. We started from preparing composites through different methods and building the structure of the sulfur electrode to improve the performance of sulfur cathode.1. Preparation of NanoS@PANI/G composite and the electrochemical properties for lithium sulfur battery.A sandwich-structured nanoS@PANI/G composite was synthesized through a facile method:polyaniline is polymerized in-situ on graphene sheets and sulfur nanoparticles are deposited into polyaniline layer simultaneously. The phase, morphology and structure of the nanoS@PANI/G composite were characterized by XRD, TG, SEM, TEM and XPS and the electrochemical properties were tested on the cell tester. We found electrode delivers a high initial capacity of 1625 mAh g-1, remaining a reversible capacity of ～600 mAh g-1 after 100 cycles. It is owing to a continuous electrically conducting polyaniline@graphene network binding with sulfur nanoparticles, high flexibility accommodating volume expansion and porous space for adsorbing the polysulfides.2. Preparation of S-nanosphere@G composite and its electrochemical properties as cathode material for lithium sulfur battery system.The sulfur nanospheres with diameter of 400～600 nm are synthesized through a solution-based approach with the existence of polyvinylpyrrolidone (PVP). Then the sulfur nanospheres are uniformly wrapped by conductive graphene sheets through the electrostatic interaction between graphene oxide and PVP, followed by reducing of graphene oxide with hydrazine. The phase, morphology and structure of the S-nanosphere@G composite were characterized by XRD, TG, SEM and TEM and the electrochemical properties were tested on the cell tester. We analyze the influence of the special structure of graphene wrapped sulfur nanoarchitecture and the cycle after morphology changes. As a result, the S-nanosphere@G nanocomposite with 91 wt% sulfur shows a reversible initial capacity of 970 mAh g-1 and remaining a reversible capacity of430 mAh g-1 after 100 cycles at a rate of 0.2 C.3. Preparation of carbonized PAN nanowire interlayer and the electrochemical properties of cathode materials for lithium sulfur battery system.We prepared PAN through electrostatic spinning with the raw materials of polyacrylonitrile and N,N-dimethylformamide as solvent, then high temperature carbonized PAN nanowire as interlayer insert into cathode material and membrane. The phase, morphology and structure of the carbonized PAN were characterized by XRD, SEM and the electrochemical properties were tested on the cell tester. The electrochemical properties of cathode materials have a great improvement. The dischange capacity under various C-rates of composite kept at about300 mAh g-1 after 100 cycles.