Research On Preparation And Performance Of The Key Materials For PAN-based Lithium Sulfur Batteries

Owing to high theoretical energy densities and low cost,lithium-sulfur?Li-S?batteries have been considered as one of the most promising candidates for next-generation secondary batteries.Among various sulfur materials,S@pPAN composite material has attracted much attention due to its special structure.However,there still exist some drawbacks in this system:?1?The lithium metal anode/electrolyte interface is unstable,leading to low Coulombic efficiency,dendrites growth and safety issues;?2?The sulfur content of S@pPAN composite materials is normally less than 50 wt.%and the excessive sulfur content will cause rapid capacity decay of the cathode.To solve these problems,the key materials of lithium sulfur batteries were prepared by utilizing polyacrylonitrile?PAN?as basic raw material.The electrochemical performance of Li-S cells was improved by adopting lithium metal anode interlayer,PAN-based gel polymer electrolyte and multifunctional binder.The detailed contents and achievements are as follows:In the aspect of lithium metal anode protection,a versatile interlayer in which AlF₃ are embedded within pyrolysis PAN nanofibers?AlF₃@CNFs?was firstly prepared by a facile electrospinning method.The effects of calcining temperature and AlF₃ content on the morphology,resistivity and electrochemical performance of the interlayer were investigated,respectively.The results show that the flexible interlayer can induce controllable Li⁺deposition in which the AlF₃ reduces Li nucleation overpotential and CNFs provides high Young's moduli up to 47 GPa,thus suppressing the formation of Li dendrites.A high Coulombic efficiency?97.2%?and a long lifespan?900 h?are achieved in the carbonate electrolyte.A long cycling life?500 cycles?with high capacity retention?99.0%?is also realized by using interlayer-protected lithium anodes in Li|S@pPAN cells.For the engineering of the S@pPAN cathode,a functional binder?SA-Cu?was synthesized through the crosslinking effect of Cu²⁺ions and sodium alginate?SA?.The SEM and XPS analysis show that the robust binder can not only effectively maintain a stable electrode structure during cycling,but also avoid the polysulfide accumulation on the cathode surface.Meanwhile,electropositive cupric ions immobilize sulfur or polysulfide through chemical binding,thereby improving the cycle and rate performance of high content S@pPAN cathode?ca.52.6 wt.%?.At 1 C,the specific capacity retention of S@pPAN/SA-Cu0.1 cathode can reach 73.7%after 1000 cycles in the carbonate electrolyte,which is much higher than that of the cathodes with PVDF and C-?-CD binders.In addition,a long cycling life and enhanced rate performance are also realized in the ether-based electrolyte.Moreover,the performance of high content S@pPAN cathode with SA-Co and SA-Ni binders has also been investigated.In the modification of gel electrolyte,AlF₃@PAN gel electrolyte prepared by electrospinning method was demonstrated to be compatible with lithium metal anode.When adding 20 wt.%AlF₃,gel electrolyte possesses highest electrolyte uptake and widest electrochemical window.Finally,a quasi-solid-state PAN-based Li-S battery with 20%AlF₃@CNFs as lithium metal anode interlayer,20%AlF₃@PAN as gel electrolyte and S@pPAN/SA-Cu0.1 as cathode was assembled.The cell exhibits good interface compatibility,stable cycling performance and long lifespan even under high-current density.