The Effect Of Nano Structure Of Interface On Electrochemical Performance Of Lithium Sulfur Batteries

Lithium-ion batteries are widely used in the field of energy storage because of their advantages of light weight,low cost and high energy density.Lithium-sulfur?Li-S?batteries,which coexistence of high specific capacity(1675 m Ah g^-1)and energy density(2600 Wh kg^-1),have drawn increasing interest due to their low cost and environmental friendly.Unluckily,their implementation has been baffled by a series of reasons,including week cycle life,and low capacities,which are caused by:1)rapid dissolution of lithium polysulfide?Li₂S_n?species into the electrolyte during the recharge,2)low electronic conductivity of both sulfur and lithium sulfide.In this work,Li-S batteries with high performance and high stability were prepared through the improvement of cathode,current collector,active material and separator.The researches are as follows:?1?Using the interaction between polar materials and polysulfides,we have grown WS₂ nano sheets on carbon fibers?CC@WS₂?and TiO₂ nanowires?CC@TiO₂?.On the one hand,the introduction of nano chips or nanowires greatly increases the specific surface area of carbon nanofibers,which provides sufficient sites for the transport of lithium ions and the conversion of polysulfides in the electrochemical process;on the other hand,WS₂ and TiO₂ have strong interaction with polysulfides to avoid the loss of active materials and improve the cycling performance of the battery.The results show that even after 1500 cycles at a rate of 2 C,the battery still maintains about 90%specific capacity with a high specific capacity of 502 m Ah g^-1.The novel CC@TiO₂/S composite cathode exhibits a high initial capacity of 324 m Ah g^-1 at 5 C.?2?The backbone of the PIP and interlayers of the Ti₃C₂T_x act as the supporter for the porous structure sulfur before electrochemical operation.The unsaturated chemical bonds and the functionalized C-O and C-C bonds render the PIP as molecular target to control the nucleation and heterogeneous growth of Li₂S during discharge.Instead of the compact insulting Li₂S layers on the host,3D porous Li₂S island growth is achieved,which effectively defers the surface passivation of the host under long-term operation of Li-S batteries.As a result,the Ti₃C₂T_x/PIP@S cathode delivers a high capacity of 1510m Ah cm^-1 at 0.1 C and remarkably improved cycling stability.?3?By directly coating a thin layer of reduced graphene oxide?rGO?/sodium lignosulfonate?SL?composite on the standard polypropylene?PP?separator,we produce a rGO@SL/PP separator with abundant negatively charged sulfonic groups in the porous lignin network,which effectively suppress the translocation of the negatively charged PS ions without compromising the transport of positively charged Li⁺ions.Using the rGO@SL/PP separator,we demonstrate a highly robust Li-S battery with a capacity retention of 74%over 1000 cycles.?4?Using electrospun,we report a non-flammable multi-functional separator for efficient suppression of PS dissolution and high temperature performance of Li-S batteries.Polyacrylonitrile?PAN?and ammonium polyphosphate?APP?are electrospun into a multi-functional separator?PAN@APP?for stable and safe Li-S batteries.Owing to the abundant amine groups and phosphate radical in APP,the PAN@APP separator has strong binding interaction with PS,which exerts strong charge repulsion to suppress the transport of negatively-charged PS ions and free radicals.This work provides a robust materials platform for stable and safe Li-S batteries and points to a direction to close the current gap facing the commercialization of high-energy next-generation electrochemical conversion/storage devices.