Study On Preparation And Characterization Of Li₂MnSiO₄and Polyaniline Nanomaterials Of Energy

Lithium ion battery and supercapacitor have both been the new energy storagedevices of extensive research in recent years. In this paper, imidazolium-based ionicliquids as solvents and potential structure-directing agents, ionothermal synthesis ofLi2MnSiO4as cathode material for lithium-ion batterie and synthesis of polyaniline(PANI) particles via chemical polymerization in ionic liquid were explored,respectively. The structures, morphology and electrochemical performance ofmaterials were characterized by X-ray diffraction (XRD), field emission scanningelectron microscopy (FESEM), Brunauer–Emmett–Teller (BET), galvanostaticcharge–discharge and electrochemical impedance spectroscopy (EIS) tests.The effects of ionic liquid species, calcining temperature and time, coated carbonand other factors on the preparation and performance of the cathode material wereinvestigated. The results are as follows:(1) Uniformly dispersed, regularly-shapedand homogeneous Li2MnSiO4precursors with a space group of Pmn21could beobtained via ionothermal synthesis in imidazoliumbased1-ethyl-3-methylimidazoliumtetrafluoroborate ([EMIM]BF4) and1-butyl-3-methylimidazolium tetrafluoroborate([BMIM]BF4) ionic liquids under the mild conditions of low-temperature and ambientpressure.(2) The crystal structure of obtained Li2MnSiO4after calcination processmore stable than that of precursors, which result in further differentiation ofnanoparticle size followed by different calcination temperature. The sizes ofLi2MnSiO4powders were prepared at750°C range from150to280nm. However,the powders were prepared at600°C with the diameter in the range of120–150nm.(3) Carbon coated could decrease electrochemical impedance and charge transferresistance, increase the electronic conductivity and improve the electrochemicalperformance. Li2MnSiO4/C obtained after carbon coated exhibits favorableelectrochemical properties with a maximum discharge capacity of218.2mAh/g andretained80%after50cycles at a current density of0.1C. Also with a good high-rateability, the initial discharge capacity at5C is determined as140.4mAh/g. However,Li2MnSiO4cathode shows the specific capacity of167.5mAh/g and just retained69%after50cycles at0.1C. At the same time shows poor rate performance, the specificcapacity at5C is only96.5mAh/g.In the study of the preparation of PANI particles via chemical polymerization inionic liquid, we mainly investigated the effects of ionic liquid species and deionized water on the preparation, structure and performance of the material.The results revealthat:(1) These samples synthesized in [EMIM]Br and [EMIM]BF4ionic liquidspresent spherical structure with different sizes (about100nm in [EMIM]Br and about50nm in [EMIM][BF4]). However, the as-prepared PANI using water as reactionsolvent presents random stacking claviform with size of250nm.(2) The PANIobtained via same temperature and different reaction times were characterized, thepossible reaction mechanism and the effect of ionic liquids as solvents and templateagent were analyzed.(3) The performance of the samples prepared in ionic liquids arebetter than these prepared in distilled water, through the electrochemical performancetests. The PANI prepared through [EMIM]Br,[EMIM]BF4and water with an initialcapacity of520,625and342F/g, and retained an effective capacity of465,566and256F/g after2000cycles at current density of0.1A/g, respectively. Furthermore, thePANI obtained in [EMIM]BF4displays excellent rate performance with thecapacitance of590,575and522F/g at0.2,0.5and1.0A/g, and shows the lowestcharge transfer resistance (0.55) by the electrochemical impedance spectroscopy(EIS) measurements.