Preparation And Electrochemical Performance Of Polythiophene And Bismuth Sulfide For Aluminum Ion Batteries

As a new generation of rechargeable secondary batteries with potential for development,aluminum-ion batteries are currently the focus of research.Aluminum atom have three electrons transferred when it participate in the redox reaction,which makes the aluminum ion battery have a high theoretical capacity.It uses room temperature ionic liquid as the electrolyte which is not flammable,so it has high safety.In addition,aluminum resources are richer than lithium resources,and the preparation is simple and the cost is low.The development of cathode materials suitable for aluminum ion batteries with high energy density is the focus of current research.At present,carbon-based materials,transition metal compounds,and conductive polymer materials are several types of materials that people are more concerned about.In this paper,a conductive polymer polythiophene was prepared and compounded with graphite by ball milling to obtain a polythiophene/graphite composite material.The electrochemical performance and electrode reaction mechanism of the composite were studied,as well as the effect of the graphite content on the electrochemical performance of the composite.The experimental results show that compounding with graphite can increase the capacity of the electrode.When the mass ratio of polythiophene to graphite is 1:1,the discharge capacity of the polythiophene/graphite composite positive electrode is the largest,which can provide the discharge capacity of 150 mA h g-1 under the current density of 500 mA g-1.In addition,under the high current densities of 2 A g-1 and 5 A g-1,the discharce capacity of 85.7 mA h-1 and 75.5 mA h g-1 can still be provided after 500 cycles.The polythiophene/graphite composite shows good Cyclic stability.Then Bi2S3 nanorods and Bi2S3/MoS2 nanorod composites were prepared by hydrothermal method,and their electrochemical properties were tested.The results show that the aggregation of single nanorods and the growth of MoS2 significantly inhibit the radial growth of nanorods.The Bi2S3 nanorods have a very high first-cycle specific discharge capacity of 251 mA h g-1.The Bi2S3/MoS2 composite nanorods have high cycle stability.After 100 weeks,the specific discharge capacity is 132.9 mA h g-1,and the Coulomb efficiency is 93.7%.The Bi2S3 has a typical layered structure,and its charge and discharge mechanism is consistent with the traditional ion insertion and deinsertion.During charging,AlCl4-ions are embedded in the interstitial positions in Bi2S3,and during discharging,the ions are released.After compounding with MoS2,the formation of the Bi2S3/MoS2 interface structure and the coating of MoS2 inhibited the volume expansion of the Bi2S3 nanorods during charging,and the ultra-thin MoS2 nanosheets maintained the long cycle stability.This makes Bi2S3/MoS2 nanorods have better cycle stability than Bi2S3 nanorods.Finally,a new Al-Ni battery was assembled with high-purity Ni foil as the positive electrode,high-purity Al foil as the negative electrode,glass filter as the separator,and AlCl3/[EMIm]CI ionic liquid as the electrolyte.The reversible reaction of the battery was achieved in a weak Lewis acid electrolyte with a molar ratio of AICl3 to[EMIm]Cl lower than 1.1:1.We investigated the electrochemical performance of electrolytes with molar ratios of 1.09,1.07,and 1.05,and discussed the charge and discharge mechanism and failure process of the battery.The conclusions are as follows:the discharge capacity of Al-Ni batteries increases with the increase of the molar ratio of AICk3 to[EMIm]Cl in the electrolyte,and the coulomb efficiency decreases with the increase of the molar ratio.The charge-discharge process of Al-Ni batteries can be divided into three stages.During the discharge process,a series of nickel-aluminum intermetallic compounds AIxNiy are produced on the positive electrode Ni foil;the side reaction products of the battery are mainly Ni(ClO4)2 and AICl3O12,may also include NiO,Ni2O3 and NiCl2.Some side reaction products enter the electrolyte and are adsorbed on the separator,hindering ion migration and increasing battery internal resistance.The remaining side reaction products are deposited on the Ni foil.As the number of cycles increases,the deposits accumulate into a sheet,which gradually isolates the contact between the Ni foil and the electrolyte,making the electrode reaction unable to continue and the battery failure.