The Research On Constructing The Key Materials Of Sulfur Cathode For Lithium-Sulfur Battery With High Sulfur Loading And High Performance

With the rapid development of portable electric and electronic devices,it is urgent to develop energy storage batteries with high energy density and long service life.The commercial lithium-ion batteries have not met the markets demand due to their inherent limitation of gravimetric energy density.Among the energy storage devices,rechargeable lithium-sulfur?Li-S?battery is considered to be one of the most promising high-energy-density electrochemical energy storage system owing to its high theoretical energy density of about 2600 Wh kg^-1.And,sulfur as electrode material has other advantages such as low cost,environmental friendliness.However,the commercialization of Li-S battery is impeded by the low sulfur utilization,low Coulombic efficiency,fast capacity fade and poor cycle life.These problems mainly arise from the poor electrical conductivity of sulfur and Li₂S,the heavy dissolution and“shuttle effect”of polysulfides,the volume expansion,and the severe corrosion of lithium metal anode during cycling.Additionally,the low sulfur content and low sulfur mass loading in sulfur electrode also inhibit the commercialization of Li-S battery.To address these problem and improve the performance of Li-S battery,this dissertation mainly focuses on the construction of sulfur electrode with high sulfur loading,the design of functional binder,the modification of separator and the design of gel polymer electrolyte.The following is the detail.?1?The construction of sulfur electrode with high sulfur loading.A high sulfur content N-PCB/S composite material with the core-shell structure has been successfully prepared by depositing sulfur onto pigment carbon black with grafting long chain quaternary ammonium ions via a facile method.On the basis,sulfonated acetylene black was coated on the CS particles homogeneously,which could further improve the electronic conductivity of the composite.A high areal capacity of 6.0 mA h cm^-22 over 50 cycle was achieved for the sulfur electrode with sulfur mass loading of 6.7 mg cm^-2.This electrode is very promising for the high-energy-density Li-S batteries.?2?The design of functional binder.The multidimensional polymer with quaternary ammonium cations??-CDP-N⁺?and the comb-like poly-sulfide polymer?PSPEG?were prepared and utilized as multi-functional binder for sulfur electrode.The unique structure unique the?-CDP-N⁺binder some new abilities:a sulfur-electrode-stabilized ability,a polysulfides-immobilized ability,and a volume-accommodated ability.Hence,the?-CDP-N⁺-based cathode demonstrates improved cycling performance and rate capability compared to those of cathodes with other well known binders.Even with a high sulfur mass loading of 5.5 mg cm^-2,the cathode with?-CDP-N⁺still can deliver a higher areal capacity of 4.4 mAh cm^-2.The PSPEG polymer consist of a mass of polysulfur?S_x?bonds on the main chain and low-molecular-weight PEG on the side chain.It was found that the S_x bonds could improve the electrodeposition states of Li₂S and suppress the agglomeration of irreversible Li₂S.And the ether oxygen group of PEG on the side chain wouldincrease Li+migration rate and improve the rate performance of Li-S batteries.The main highlight is that the PSPEG electrode also exhibit a good electrochemical performance when the PSPEG content of sulfur cathode was decreased to 1 wt%.This research work would put forward the development of Li-S batteries.?3?The modification of separator.a functional separator coated by sulfonated carbon was prepared for improving the overall performance of Li–S batteries.The sulfonated carbon coating not only could intercept polysulfide anions but also could function as an upper current collector to facilitate electron transport for enhancing the electrochemical utilization of sulfur.The ABS coating layer is only 0.13 mg cm^-2,therefore,the negative effects of the added weight of the ABS coated layer could be ignored,such as decrease in the sulfur content of the cell,which would decrease the energy destiny of the cell.?4?Base on the above results,the sulfur electrode with high sulfur loading,functional binder??-CDP-N⁺?and ABS separator are combined to fabricate high-performance Li-S coin cell and soft package cell.The Li-S coin cell could deliver a high capacity of 998 mA h g^-11 at 0.2C rate after 200 cycle.And the soft package Li-S cells also could demonstrated the high capacity over 1000 mA h g^-1.More importantly,the whole energy density of the soft package Li-S cell is as high as 300 Wh/kg,which is also much higher than that of the commercialized Li-ion battery.Hence,this kind of Li-S cell has a great application prospect.?5?The design of gel polymer electrolyte.A gel polymer electrolyte?PEGCD/HEC?with high high ionic conductivity?5.62×10^-44 S/cm,25??was prepared.And the Li-S battery using the gel polymer electrolyte PEGCD/HEC displays good cycle performance and high coulombic efficiency.