Tunable Porous Structure Of Dickite For Energy Storage Battery Application

The separator,which affects the interfacial structure,capacity,stability and cycle life of the battery,is one of the four components of lithium ion batteries.At present,the common commercial separator is polyolefin separator because of its many advantages.However,the poor thermal stability and electrolyte wettability of polyolefin separators lead to frequent safety accidents.Therefore,the development of high-performance separator is an effective means to improve the safety of batteries.In this paper,intercalation and chemical reaction were applied to adjust the pore structure of the dickite and further regulated the pore structure of the coated separator.The porous morphology of dickite is formed by expansion agent and initiator on the condition of high temperature.The intercalation complexes were prepared by two kinds of expansion agent（thiourea and urea）with similar structures.The results of XRD and FTIR show that two kinds of expansion agent can intercalate dickite interlayer,and expand the interlayer spaces of dickite.The intercalation of thiourea into the interlayer spaces of dickite requires multiple displacement intercalations of organic molecules,while urea is more likely to form intercalation complexes.The TG-DTA results show that the mass ratios of urea and potassium chlorate could control the expansive degree of dickite.The size of the slit pore of porous dickite increases with the increase of the mass ratios of urea to potassium chlorate.After calcining the mixture of 40 wt%potassium chlorate and urea/dickite intercalation complex with a mass ratio of 3/4,the dickite forms the porous structure with channel gap of 0.212μm.In order to investigate the effects of dickite with tunable pore structure on the electrochemical performance of the coated separator,the performance of the coated separator in two different battery systems was tested.The samples were prepared by dip coating method with acrylonitrile polymer（LA133）as a binder.The experimental results show that the increased content of the porous dickite is beneficial to improve the pore structure of the coated separator,especially the porosity.Porous dickite can improve the wettability of the separator and the interfacial stability between the electrode and the electrolyte.The separator coated with porous dickite has higher mechanical strength than the absorbed glass mat（AGM）.The ionic conductivity of the high content-porous dickite coated separator in the aqueous electrolyte with ZnSO₄ and Li₂SO₄ is 13.12 mS/cm.In addition,the porous dickite enhances the dimensional stability of the nonwoven fabric.In rechargeable hybrid aqueous batteries with Zn/LiMn₂O₄,the porous dickite can effectively suppress the ohmic polarization and reduce the interfacial resistance.The high content-porous dickite coated separator exhibits high discharge specific capacity and superior C-rate stability.The capacity retention is 87%after 100 cycles,which is 5%higher than that of AGM.The study confirms that dickite with different expansive degree plays a vital role in optimizing the pore structure of the separator.A good pore structure can increase the porosity and electrolyte uptake of the separator.In addition,the hydroxyl group of the porous dickite contributes to the ion migration,suppresses electrode polarization,and reduces internal loss of the battery.The separator shows favorable affinity for both organic and aqueous electrolytes resulting superior ionic conductivity（3.157mS/cm）and lithium transference number（0.64）using organic electrolyte with LiPF₆（EC/DEC,1/1 by volume）.Moreover,coated separator exhibits the excellent thermal stability.In lithium ion battery with Li/LiFePO₄,the coated separator with optimized pore structure displays high capacity and excellent rate capability.Furthermore,the cells show capacity retention of 93.4%after 200 cycles.