Controllable Preparation Of Highly Compatible Sulfurized Polyacrylonitrile Nanofiber Cathode And The Study Of Inhibiting Molecular Rearrangement

The burning of traditional fossil fuels has provided more than 80%of energy consumption in the development of human society.The resulting environmental pollution and energy depletion have made the storage and utilization of renewable resources an important issue in the process of social development.Lithium-sulfur batteries with sulfur as the positive electrode have attracted extensive research interest due to their inherent high theoretical capacity and low manufacturing cost.However,the sulfur cathode has electronic insulation,and the formation of soluble lithium polysulfide intermediate products during the cycling process leads to the collapse of the electrode structure and the rapid deterioration of the battery performance.Compared with elemental sulfur,sulfided polyacrylonitrile cathode has better conductivity and structural stability due to its unique short-chain bonding structure,which is used as an ideal material for cathode sulfur modification.At present,the development and application of SPAN are mainly affected by the following factors.On the one hand,the SPAN cathode is limited by the low sulfur saturation loading（～42wt%）,which seriously limits the energy density of the system.On the other hand,similar to the sulfur cathode,when SPAN is in the ether electrolyte,it is easy to induce the formation of soluble intermediate lithium polysulfide,which is usually considered to be the result of SPAN molecular rearrangement in the ether electrolyte.However,the mechanism of SPAN rearrangement in ether electrolytes has not been well understood.In order to deal with the above problems,we first prepared self-supporting nanofiber membranes with different porosity by changing the transverse spinning stroke in the spinning process,changed the conditional laminate electrode and analyzed the effect on electrochemical performance.in order to achieve a good balance between high sulfur load and excellent electrochemical performance.Secondly,we prepared SPAN electrodes with different morphologies,which revealed the morphology and structural effects related to the compatibility of ether electrolytes.The self-supporting SPAN cathode with three-dimensional network structure shows higher electrochemical stability than the powder cathode.Then,by reasonably controlling the molecular rearrangement of SPAN,the trace Li₂S_n generated in situ is used as a chemical medium to promote the reversible decomposition of Li₂S,which provides a new direction for the cathode design of lithium-sulfur battery.The main results are as follows:（1）the self-supporting cathode can avoid the use of conductive carbon black and binder,which can effectively increase the sulfur content.In this experiment,self-supporting nanofiber membranes with different porosity were prepared by changing the transverse spinning stroke in the spinning process.Elemental analysis shows that the sulfur load of SPAN-100 is only 1.28mg cm^-2,but it has the highest stable discharge specific capacity.Then,in order to increase the unit sulfur load and increase the energy density of the battery system,the SPAN was laminated under different conditions and the effects of different lamination conditions on the electrochemical performance were investigated.The electrochemical performance and sulfur load were compared comprehensively.The double-layer laminated SPAN-2-CP electrode has a unit sulfur load of 2.23 mg cm^-2,and the discharge specific capacity is stable at 1130.8 m Ah g^-1 after 200 cycles.It can effectively achieve a good balance between high sulfur loading and excellent electrochemical performance.（2）SPAN electrodes with different morphologies were prepared by electrospinning and slurry coating.The morphology-property relationship of SPAN in ether electrolyte was analyzed and compared,and the single-phase solid-solid conversion between SPAN and Li₂S was realized.Material and electrochemical characterization show that SPAN exposed to a large number of fragments in the electrolyte is easy to induce the continuous release of short-chain sulfides from SPAN.Due to the polysulfide shuttle effect,the uncontrolled rearrangement of SPAN will lead to the deterioration of the long-term cycle.Due to the small exposure area,the self-supporting fiber electrode can effectively protect SPAN from the strong interaction of electrolyte,which is very important to stabilize the cycle performance and cycle life of the battery.However,the solid-solid reaction between SPAN and Li₂S is an obstacle to the realization of rapid reaction kinetics.Therefore,we regulate the rearrangement of SPAN through the introduction of pore structure in the self-supporting SPAN electrode,avoid the shuttle effect and accelerate the previous activation process,and achieve a stable and efficient cycle of SPAN electrode in lithium-sulfur battery system.