Mechanical Properties Of Li-ion Battery Separator Prepared By Directional Electrospinning

With the increasingly strong trend of energy transformation and upgrading,the existing Li-ion battery technology can hardly meet the public demand for high-performance batteries.As one of the core components of Li-ion battery,the performance of separator is one of the key factors that affecting the performance of Li-ion battery.At present,polyolefin separator occupies most of the market share of separator.In recent years,the application of polyolefin separator showed the following shortcomings:(1)low porosity and poor electrolyte wettability;(2)large thermal shrinkage to high temperature,which seriously affects the safety of Li-ion battery.Therefore,developing high-performance battery separator has become a hot topic in the field of energy storage.Electrospinning is a common method to prepare nanofiber films.Compared with other methods,electrospinning membrane has higher porosity and better wettability,so electrospinning membrane has become a hot research direction in recent years.Polyacrylonitrile(PAN),as a classical electrospinning material,has the advantages of chemical resistance and good wettability to electrolyte.However,its low strength,poor wear resistance and fatigue resistance limited the wide application of PAN separators.A lot of research work has been done to improve the physical properties of PAN membrane,but there are few reports about its mechanical properties.Polyvinylidene fluoride hexafluoropropylene(PVDF-HFP)copolymer has good elasticity and toughness,but its wettability to electrolyte is relatively poor.Therefore,we combined the advantages of PAN and PVDF-HFP and prepared PAN@PVDF-HFP(PPH)composite separators by the electrospinning method.The main contents are as follows:(1)Conventional PPH separators were prepared by electrospinning technology,and semi-aligned PAN separators and PPH separators were prepared by directional electrospinning technology.The morphology and structure of the separators were characterized by scanning electron microscopy(SEM)and X-ray diffraction(XRD).In order to further study the effect of fiber orientation on the mechanical properties of the films,several kinds of bi-directional films with different angles were prepared.(2)Based on the mean-field-homogenization theory,the mechanical parameters of the blended materials were obtained by the MF module in Digimat software package.Then the FE module was used to construct the appropriate RVE unit to simulate the mechanical response of the films with different fiber orientation.The effects of fiber orientation and fiber angle on the mechanical properties of anisotropic films were analyzed.(3)The effects of different fiber orientation and fiber angle on the mechanical properties of the films were tested by uniaxial tensile test,and compared with the simulation results.(4)The application of oriented fiber separator in Li-ion battery was analyzed by systematically characterizing the electrochemical performance of fiber separator.