Preparation Of Zirconia Fiber Paper And Its Application In Battery Separator

Lithium-ion batteries(LIBs)are widely used in electric vehicles and electronic products due to their portability,high energy density and long cycle time.As an important component of LIBs,separators have an important impact on battery safety performance,discharge capacity and battery life.The separators currently in commercial use are mainly polyolefin materials,and polyolefin materials are widely used due to their high mechanical strength,suitable electrochemical stability and low cost.Due to the hydrophobic surface,the polyolefin membranes have poor wettability to conventional electrolyte,which results in poor electrochemical performance.Especially when the temperature rises,the polyolefin separator will contact the positive and negative electrodes due to severe heat shrinkage,resulting in an explosion or a fire.Zirconia fiber has excellent chemical stability,high temperature resistance and good wettability to the electrolyte,and is an ideal material for battery Separators.Therefore,this paper proposes and implements the use of papermaking technology to make zirconia fiber paper as a LIBs separator.Firstly,the self-performance ofzirconia fiber was studied.Then the factors affecting the dispersion effect of zirconia fiber and the strength of zirconia fiber paper were analyzed,and the performance of ZrO2/PVDF fiber paper and ZrO2/Basalt fiber paper in battery separator were studied,respectively.The main findings are as follows:1.The properties of zirconia fiber prepared by electrospinning technology were studied.The results show that the zirconia fiber has a water absorption rate of 4.27%under the conditions of temperature and humidity of 25 0C and 65%,and the Zeta potential im water is-25.85 mV.The fiber is cylindrical,and the surface is smooth.After treatment with acid-base solution,the surface morphology of the fiber does not change,which proves that zirconia fiber has excellent resistance to acid and alkali corrosions.2.The effects of zirconia fiber treated by different processes and different dispersing agents and adhesives on fiber dispersion and fiber strength were studied.The results showed that when the concentration of suspension slurry was 0.2%and the number of resolving revolutions was 20.000 rpm,the obtained zirconia fiber has the best dispersion effect.The polyethylene oxide having a concentration of 2%has the best dispersion effect on the fiber.The strength of zirconia fiber paper prepared by PVDF as adhesive can reach 4 MPa,which is far superior to fiber paper prepared by using PVA as adhesive.Zirconia and basalt composite fiber paper has a higher strength at high temperatures.3.By changing the concentration of PVDF in the fiber suspension,zirconia fiber paper with different PVDF contents was made.Their surface morphologies,porosities.electrolyte absorption rates,strengths and XRD patterns were investigated.ZrO2/PVDF fiber paper with PVDF content of 40%was selected to investigate the separator properties.The results show that when the PVDF content is 40%.the pores in the zirconia fiber paper has the best morphology,the largest number and the most uniform distribution.Porosity and electrolyte absorption tests also showed that ZrO2-40%PVDF fiber paper has the highest porosity and electrolyte absorption rate,which are 77.69%and 523.3%,respectively.PVDF in fiber paper is amorphous,which helps to improve the wettability of fiber paper.ZrO2-40%PVDF fiber paper has better flexibility,tensile strength is 4.7 MPa.and the contact angle with electrolyte is only 0,which can help the diaphragm to store more electrolyte and improve the electrochemical performance of the battery.The heat shrinkage of ZrO2-40%PVDF fiber paper at 500℃ is 0.zirconia fiber paper can obviously improve the safety performance of LIBs.improve the properties of batteries at high temperatures.The oxidative decomposition voltage of ZrO2-40%PVDF fiber paper is 4.8 V,the ionic conductivity is 0.96 mS cm-1.the initial discharge specific capacity and the capacity retention after 100 cycles are 134 mA h g-1and 89.6%,which are better than of PP separator,i.e.129.9 mA h g-1and 84.5%.ZrO2-40%PVDF fiber paper also has better discharge performance at different magnifications than PP separator.4.ZrO2/Basalt fiber papers with different basalt fiber contents were prepared by paper-making technology.The tensile strengths of ZrO2/Basalt fiber paper with different basalt fiber content were tested,and the fiber paper which meets the strength requirements of the diaphragm was selected for battery separator performance test.The results show that when the basalt fiber is added to 50%,the strength of the fiber paper reaches 2.4 MPa,which satisfies the mechanical stress requirement of the battery.In ZrO2/Basalt fiber paper,the zirconia fiber and the basalt fiber are evenly dispersed in the fiber paper.The fiber paper contains a large pore size,which can increase the porosity of the separator and prevent the growth of lithium dendrites.The porosity and electrolyte absorption rate are 80.36%and 594.65%,respectively,and those of PP are only 46.78%and 114.29%.It shows that ZrO2/Basalt fiber paper has greater porosity and liquid absorption rate,which is beneficial to improve the discharge performance of the battery.After heat resistance test,ZrO2/Basalt fiber paper did not undergo any dimensional change at 200℃,and the PP separator had severe shrinkage at 150 ℃.ZrO2/Basalt fiber paper can be well isolated to improve the safety of LIBs.The oxidative decomposition voltage of ZrO2/Basalt fiber paper is 4.7 V,the ionic conductivity is 0.82 mS cm-1,the initial discharge specific capacity and capacity retention after 100 cycles are 133.1 mA h g-1 and 92.3%,higher than those of PP separator,i.e.129.9 mA h g-1and 84.5%.The discharge performance of ZrO2Basalt fiber paper at different magnifications is also significantly better than that of PP diaphragm,so it can be used under at high temperatures and under high current conditions.