Fabrication Of Polyphenylene Sulfide Fiber-based Composite Lithium-ion Battery Separator Through Paper Making Method

Rechargeable lithium-ion batteries?LIBs?,as an important energy storage device in developing renewable energy,have been awarded the 2019 Nobel Prize in chemistry.In the battery components,separator physically separates the cathode and anode to avoid internal electrical short-circuit while serving as electrolyte reservoir to ensure free transfer of lithium ions,thus playing a vital important role in cell performance and safety.Microporous polyolefin membrane has been widely used as separator in LIBs recently due to their advantages of superior mechanical strength and uniform aperture distribution.However,the polyolefin separator still has some defects.Firstly,the low thermal stabilities of polyolefin make them suffer from severe shrinkages with the increase of battery temperature,which may lead to safety risk of LIBs.Secondly,the nonpolar polyolefin separator has poor compatibility with polar liquid electrolyte,which may effect on the electrochemical performance of cells.Polyphenylene sulfide?PPS?fiber is a kind of high performance fiber with outstanding thermal stability,inherent flame resistance and excellent chemical resistance.It may be a promising substitute for polyolefin material applied as separators in battery.But the pure PPS membrane can could not be used as separator directly due to the large and non-uniform pores,which may cause internal short-circuit.Physical coating is a common method to optimize the pore structure of substrate,but the separator with physical coating has an inferior long-time cycling stability.Therefore,it is supposed to think about the inside of the substrate to optimize the pore size of PPS membrane.In this project,we adopted aramid nanofibers?ANFs?and cellulose fibers?CFs?to compound with PPS fibers by using a facile papermaking method.And the performance of the prepared composite membranes was comprehensively evaluated,the main research results are summarized as follows:?1?ANFs with high specific surface area could be a mediator to fill in the large pores created by the networks of PPS fibers,which endows the ANFs/PPS composite membrane with three-dimensional porous structure.Therefore,in this study,PPS fibers was firstly pulped and then mixed with ANFs suspension to obtain the composite ANFs/PPS separator by a simple papermaking process.The results show that the ANFs/PPS membrane has excellent physical parameters of porosity,liquid electrolyte wettability,thermal stability,mechanical property and ionic conductivity.Furthermore,the performances of ANFs/PPS separator were evaluated in Li Fe PO₄/Li half cells,and their discharge rate performance and cycle stability are better than that of Celgard 2400separator.?2?Considering the complicated preparation process and high cost of ANFs,cellulosic fibers?CFs?from tissue,a biomass material with high safety and low cost,were used to replace ANFs.In this study,CFs and PPS fibers were firstly pulped with high strength,and then the composite CFs/PPS separator was also prepared by papermaking process.Experiments have found that,through an intensity beating process,fibrillation of CFs can also regulate the large pores in PPS membrane,while CFs endows CFs/PPS composite separator with excellent electrolyte absorption and wettability,thus exhibiting superior ion conductivity(1.43 m S cm^-1)which is about 5times that of Celgard 2400 separator.These behaviors were finally confirmed to endow CFs/PPS-based cell with better C-rate capability and cycling performance compared to the cell with Celgard 2400 separator.In addition,the excellent heat tolerance and mechanical properties of CFs/PPS separator also provide a guarantee for the safety of LIBs.Considering the attractive advantages of CFs/PPS composite separator and the possibility of large-scale production,we believe that the CFs/PPS composite separator has practical application value.