Preparation And Properties Of Halloysite/Polyvinylidene Fluoride Composite Membranes And Silicon Anode Materials

The rapid development of portable electronic equipment,electric vehicles and large-scale energy storage systems has put forward higher requirements for high-energy density and long-cycle life lithium-ion batteries.Among them,the membranes and anode materials are the key constraints to the performance of lithium-ion batteries.In this paper,polyvinylidene fluoride?PVDF?and halloysite?HNT?were used as the basic materials to prepare the HNT/PVDF composite membrane by phase transfer method.The results of XRD and FTIR show that HNT has been incorporated into the PVDF matrix.The effects of HNT on the crystallinity,morphology and electrochemical performance of the membranes were mainly investigated.DSC test results show that as the HNT content increases,the crystallinity of the HNT/PVDF composite membrane gradually decreases.SEM results indicate that with the increase of HNT content,the number of pores on the surface of HNT/PVDF composite membranes first increase after reduction.When 4 wt%HNT was incorporated,lots of pores were formed on the surface of the 4-HNT/PVDF membrane and its porosity reached 77.94%.These pores not only can effectively store the electrolyte,but also facilitate the rapid transport of lithium ions.In addition,HNT/PVDF composite membranes were applied to Li/LiFePO₄ lithium-ion batteries.It was found that with the increase of HNT content,the battery's discharge capacity increased first and then decreased.The 4-HNT/PVDF membrane assembled battery exhibits excellent initial discharge capacity,cycle performance and rate performance.In this paper,silicon nano-particles were prepared using perlite as a silicon source precursor and a magnesiothermic?Mg?reduction method.Meanwhile,the effects of different content of sodium chloride?NaCl?on the specific surface area,morphology and properties of the obtained silicon nanoparticles were discussed.The BET results indicate that as the NaCl content increases,the specific surface area of the silicon nanoparticles also gradually increases.When the mass ratio of perlite to Mg powder and NaCl is 1:0.8:4,the specific surface area of the obtained silicon nanoparticles reaches 176.25 m²g^-1.The results of SEM and TEM show that with the increase of NaCl content,the obtained silicon nanoparticles gradually transition from the aggregation state of large particles to small particles with good dispersibility.The obtained silicon nanoparticles were applied to button battery.Low surface area of silicon nanoparticles results in low charge and discharge capacity of the battery.On the contrary,large surface area of silicon nanoparticles leads to high battery charge-discharge specific capacity.However,the specific capacity of silicon suffers a rapid decline during the charge and discharge process.In order to alleviate the above problems,a porous carbon shell was successfully coated on the surface of silicon nanoparticles by pyrolysis using chitosan as a carbon source and zinc chloride?ZnCl₂?as a pore-forming agent.By controlling the content of ZnCl₂,the structure and number of pores on the surface of the carbon shell were investigated.The results show that as the content of ZnCl₂ increases,the number of pores on the surface of the carbon layer coated with silicon nanoparticles gradually increases.When the mass ratio of ZnCl₂ to CS reaches 5 times,a large number of nanopores?4-6 nm?were generated on the surface of the carbon layer coated with silicon nanoparticles.These nanopores facilitate the rapid transport of lithium ions and promote the improvement of electrochemical performance.In addition,the battery showes a high initial discharge and charge specific capacity(2811.36 mAhg^-1/2064.11 mAhg^-1 at 0.2 C),good cycling performance(with a reversible capacity of 1301.56 mAhg^-1 at 0.2 C and capacity retention rate reaches 72% after 100cycle) and rate performance.