Design And Preparation Of Bio-based Polymer Gel Electrolyte And Study On Their Performances

With improving properties of lithium batteries(LBs)and expanding their application areas,the issue of safety become more and more serious in traditional LBs based on liquid electrolytes.In addition to its leak and inflammable,liquid electrolyte is easy to cause some severe problems when using in high-performance lithium(Li)metal batteries,such as instability of electrode electrolyte interface,structural collapse of cathode,shuttle of transition metal ions or polysulfides,Li dendrites and so on.Gel polymer electrolytes(GPE)have been considered as one of the best candidate to replace the commercial separator and liquid electrolytes.In comparison with solid polymer electrolyte involving low ionic conductivity at room temperature,GPEs are consisted of liquid electrolyte and polymer skeleton,and they possess high ionic conductivity,high Li-ion transference number,wide electrochemical stability window and infrequent electrolyte solution leakage.The reported skeletons of GPE are synthetic polymer materials,which will bring environmental pollution in the recovery batteries.The preparation of these skeleton materials get into trouble of use and release of vast poisonous and harmful solvent.Moreover,to meet the high-performance electrode materials,GPEs are expected to solve the issues and challenges these advances electrode materials facing in practical application.Therefore,in this work,beginning from some topics that including the safety of battery,environmental protection of raw material and its forming process,and feasibility of matching high-performance electrodes,the GPE consisted of electrospinning bio-based polymer skeleton are successfully designed and fabricated.The relationship is systematically studied that component,morphology and structure of bio-based membrane skeleton and electrochemistry properties of the corresponding GPE.Furthermore,a bio-based nanofiber membrane is chosen because of abundant raw materials and green forming process,which is used to build GPE with excellent performance and multi-functionality through structural design for high-safety and high-performance LBs.In the meantime,the component-structure-functionality-performance relationship is established.(1)Through the proper collocation of polymer materials,a biodegradable nanofiber membrane skeleton is successfully prepared by electrospinning.After activation by liquid electrolyte,a bio-based GPE with the rigid and flexible integration is fabricated.The poly-L-lactic acid(PLLA)with flexible chains can promote the transmission of Li ions,and the cellulose acetate(CA)with rigid chains can provide excellent mechanical and thermal properties.In addition,the low-cost halloysite nanotubes(HNTs)were first incorporated to improve the ion transfer and optimize electrode electrolyte interface in GPEs.The CA/PLLA/HNT nanofiber membrane exhibits low crystallization behavior,enhanced thermal stability and high saturated electrolyte uptake.The ionic conductivity of resultant GPE can be up to 1.52 � 10-3 S cm-1,which is far larger than other bio-based GPEs.The cycle performance and rate performance of the cells with the GPE involving CA/PLLA/HNT membrane is superior to those of the commercial separator.(2)Due to its rich source and green electrospinning process,a natural soy protein isolate(SPI)with potential in transferring Li ion is successfully used to fabricate bio-based biodegradable nanofiber membrane.The preparation is green and environmental protection because of use of water-based spinning solution.SPI-nanofiber membrane exhibits good affinity to liquid electrolyte and high saturated electrolyte uptake because SPI possesses amount of polar groups.After geltation,the corresponding GPE displays good compatibility with Li electrode and high ionic conductivity,reaching a maximum value of 3.80�10-3 S cm-1.(3)To further develop the value of bio-based GPE,a bi-functional and bio-based composite GPE(c-GPE)is successfully created to simultaneously deal with the two critical issues that Li meatal anode and LiMn2O4 cathode facing.The skeleton of c-GPE is constructed from a sandwich structure composed of porous polydopamine spheres and two layers of SPI-based nanofiber membrane,and the carbonized polydopamine spheres are coated on the surface of the membrane.The preparation process is a facile and innocuous,and the skeleton material displays excellent thermal stability and good affinity to liquid electrolyte.The c-GPE not only improves the safety of LiMn2O4/Li cell,but also exhibits significant functions of effective mitigation of the dissolution of Mn ions,and chelation of the fleeing Mn ions,as well as the dramatic suppression of Li dendrite growth.The LiMn2O4/c-GPE/Li cell displays a high capacity retention of 71.3%at 0.2 C after 200 cycles,which is 1.2 times than that of corresponding cell with commercial separator.The cell involving c-GPE shows reversible capacity of 65.5 mAh g-1 at 2 C,while the cell with commercial separator shows only reversible capacity of 9.8 mAh g-1 at 2 C.(4)To develop the next-generation Li metal battery based on sulfur(S)cathode,an optimum carbon fiber interlayer integrated with SPI-based GPE(CT-GPE)is firstly designed.The SPI-based nanofiber is directly electrospun on the preferred carbon fiber interlayer to form the composite structure,which can fully apply the functions of interlayer and GPE in Li-S battery.The optimal carbon fiber interlayer can reactivate the immobilized polysulfides,and the SPI-based GPE demonstrates high ion transfer performance.Therefore,the Li-S battery involving CT-GPE shows a great improvement in the electrochemical performance compared with that of the cell based on commercial separator.