| With the development of today’s society,the shortage of fossil energy and in-creasing environmental pollution has created more demand for green,environmen-tally friendly and sustainable efficient secondary energy storage devices.The core of high-performance battery research and development is to improve the battery’s en-ergy density,power density,cycle life.However,due to the limited theoretical spe-cific capacity of lithium ion batteries,it is very difficult to further improve the ener-gy density.Lithium-sulfur battery is a kind of lithium battery with sulfur element as positive electrode and metal lithium as negative electrode;and sulfur has a high the-oretical specific capacity of 1675 mAh g-1,and its theoretical specific energy can reach 2600 Wh kg-1,which is 35 times of the energy density of traditional lithium ion battery.In addition,sulfur is abundant in resources,cheap and environmentally friendly,so lithium sulfur batteries have attracted great attention from a large num-ber of researchers.The porous biomass carbon materials with abundant raw material sources,low price,renewable energy and high yield can improve the battery perfor-mance due to their good conductivity and high specific surface area,as well as their ability to inhibit shuttling effect by doping carbon materials with heteroatoms（N,O,P）.In this paper,we mainly study the preparation of high yield carbon materi-als from several biomasses which are easily obtained in daily life,and their applica-tions in lithium sulfur batteries:（1）Banyan has abundant renewable aerial root,namely ficus microcarpa,which is planted in a large area in south China.The porous carbon NOPC prepared from ficus microcarpa has a large specific surface area and pore volume,which has a great auxiliary role in improving the sulfur load and cylcing stability of the carbon-sulfur composite material.In addition,banyan tree also had nitrogen compounds and or-ganic compounds,so that the porous carbon material NOPC was doped with nitro-gen and oxygen.The microcosmic nanostructures of NOPC provide larger contact area and reaction sites,making carbon sulfur compounds with low sulfur content（NOPC/S-59.9%）in electrode keep higher specific capacity(1339/1008 mAh g-1)and cycle stability in the process of the electrochemical cycle,even if the compounds with a high sulfur content of 71.8%（NOPC/S-71.8%electrode）still has very good stability and high initial discharge specific capacity of 1008 mAh g-1.However,after200 cycles of NOPC/S-62.9%electrode at the current density of 0.1 C and the high current density of 1 C,the specific capacity of the electrode can still be protected at1015 and 628 mAh g-1,indicating that NOPC/S-62.9%electrode has a good cycling stability.（2）The porous carbon HPC,which takes the core of the disused bayberry as the carbon source in the rainy season,has a large specific surface area and pore volume,and can provide abundant transmission channels for electrons and ions in the cycle of the battery and greatly shorten the transport route of ions.Abundant micropores and their mesopores can effectively bind the intermediates polysulfide generated in the reaction so as to inhibit the shuttle effect and enhance the cycling stability of the battery.The electrochemical properties of carbon and sulfur compounds（HPC/S-X）with different sulfur contents and polyaniline-coated carbon and sulfur compounds（HPC/PANI/S-43.1%）prepared by hot-melt method with different proportions of carbon and sulfur were tested.In particular,the polyaniline-coated carbon-sulfur complex HPC/PANI/S-43.1%released the initial discharge capacity of 1379 mAh g-1 at 0.1 C,and remained stable throughout the 200 cycles.（3）Water system floating plant,water chestnut has strong reproductive ability and can be regenerated.The root,stem and leaf of water chestnut are generally not used by people.Because of its abundant pores and fluffy structure,it is used to pre-pare porous activated carbon skeleton.The activated porous carbon（root:RPC,stem:SPC,leaf:LPC）has a large specific surface and pore volume,and is self-doped with nitrogen,with a fluffy porous microstructure.In the experiment,the corresponding carbon-sulfur composite prepared according to carbon:sulfur=1:3,carbon-sulfur composite RPC/S-65.1%had a relatively large discharge specific capacity of 985.8mAh g-1 at the current density of 0.2 C,and the specific capacity remained at 1044mAh g-1 after 200 cycles.Even after 200 cycles at 1 C during charge and discharge,the capacity of 534 mAh g-1 is maintained,and the coulomb efficiency is always above 99%,meaning good stability. |
