Preparation Of TiN-doped PVDF-HFP Composite And Its Application As A Separator For Lithium-Ion Batteries

Lithium-ion batteries（LIBs）are high-efficiency energy storage devices and widely used in energy storage systems for portable electronic devices,electric vehicles,and power stations.However,in recent years,problems such as fire and explosion of equipment equipped with LIBs have frequently occurred,and the safety of LIBs has attracted widespread attention.As a key component of the battery,the separator can not only affect the electrochemical performance of the battery,but also separate the positive and negative electrodes and prevent the short circuit of the battery.In order to improve the safety of the separator,polyvinylidene fluoride-hexafluoropropylene（PVDF-HFP）material with excellent thermal stability and electrolyte affinity is used as the substrate to optimize the preparation process of the separator and the optimal thickness of the separator used for lithium ion battery.On this basis,the properties of composite separator is optimized by doping TiN nanoparticles with bulk phase.The main research work content is as follows:First,PVDF-HFP separators with different thicknesses are prepared by the phase inversion method,and the optimal thickness of the PVDF-HFP prepared by the phase inversion method is determined as the LIBs separator.To this end,this work carry out thermogravimetry,X-ray diffraction,and microscopic morphology analysis on the separator.And use the commercial separator Celgard2500 as a comparison to assemble the battery for electrochemical performance analysis.The results show the optimal thickness of the PVDF-HFP separator as LIBs separator is determined to be 25μm.Secondly,in order to improve the thermal and mechanical properties of the separator,PVDF-HFP is modified by doping with TiN in this experiment to prepare a PVDF-HFP/TiN composite separator with a thickness of 25μm.It is found that the addition of TiN particles can effectively reduce the crystallinity of the separator and improve the wettability of the separator to the electrolyte,thereby improving battery performance.Through a series of characterization comparisons between Celgard2500 and PVDF-HFP separators,it is found that PVDF-HFP/TiN composite separators have improved thermal properties and mechanical strength.In order to study the effect of TiN doping on the electrochemical performance,all separators are assembled into coin cells for electrochemical performance analysis.The results show that the composite separator with 12%TiN addition has the best safety performance and electrochemical performance.The battery equipped with PVDF-HFP/TiN-12 separator has a specific discharge capacity of 105 m Ah g^-1 at 10 C,and a specific discharge capacity of 156 m Ah g^-1 at 1 C.After1000 cycles,the capacity retention rate is as high as 98.7%.In this paper,the improvement mechanism of TiN for composite separator is described systematically,and the influence of microstructure,doping and chemical bonding formation of separator on the safety performance of lithium ion battery separator is revealed,and a high performance safe lithium ion battery separator composite material is obtained.In this work,the composite separator with bulk phase doped TiN particles prepared by the phase transformation method has excellent electrochemical performance,and also shows improved thermal stability and high mechanical strength,which brings excellent safety performance for the composite separator.This study lays a foundation for the development of separator materials for high safety lithium ion batteries.