Research On The Effect Of Electrolyte On Electrochemical Performance Of Supercapacitor

Supercapacitors are efficient energy storage device, which performance isbetween the chemical batteries and typical capacitors. Elements which effect theperformance of supercapacitors conclude electrode materials, electrolyte and others.The electrode materials mainly include carbon materials, metal oxides, conductingpolymer and so on. Carbon is the most widely used as the electrode material ofsupercapacitors for its good stability and low price. Conducting polyaniline （PANI）has gain wide attention due to its good performance and it can prepare PANI/activated carbon （AC） composite electrode used in the sipercapacitors. LiClO₄/acetonitrile solution has been widely concerned as the supercapacitor electrolyte,however, the lithium ion electrolyte sold in market has different effects to thesupercapacitors. It has very important significance to the supercapacitors. In this paper,scanning electron microscope （SEM）, cycle voltammetry （CV）, galvanostaticcharge-discharge test and electrochemical impedance spectroscopy （EIS） were used totest electrode materials, and the electrolyte effects to the supercapacitors werediscussed according to the galvanostatic charge-discharge test. The main contents ofthis treatise are as follows:（1） Preparation and performance tests of the AC electrode and PANI/ACelectrodeAC electrode was prepared with AC, carbon back and polyvinylidenefluoride（PVDF） as mass ratio of8:1:1. Composite electrode was prepared by CV that thePANI was deposited on the AC electrode. Then characterization and performance testsof the electrodes were carried out by SEM, CV, galvanostatic charge-discharge testand EIS. The results showed that, at a current density of3mA·cm^-2, the specificcapacitance （SC） of AC electrode was97.4F·g^-1, and the SC dropped to90%of theinitial capacity after1000cycles. However, the SC of composite electrode was340.4F·g^-1at a current density of3mA·cm^-2, obviously higher than the SC of AC electrode. The reason was that double electric layer capacitance produced by the surfacetopography of PANI and the faradic pseudocapacitance caused by redox reaction ofPANI. After1000cycles, the composite electrode also retained70%of the SC in thefirst cycle.（2） Research on the effect of electrolyte on electrochemical performance ofsymmetric supercapacitorsTwo kinds of symmetric supercapacitors （SS） with different electrolytes of1MLiClO₄/acetonitrile and NH602lithium ion electrolyte were fabricated respectively.Then they were measured by galvanostatic charge-discharge test. The result showedthat the electrochemical performance of SS with1M LiClO₄/acetonitrile was verystable, and showed the character of double electric layer capacitance. At a currentdensity of3mA·cm^-2, a potential range of [0,2.7V], the SC was52.0F·g^-1，the energydensity （ED） was50.7Wh·Kg^-1，and the power density （PD） was905.7W·Kg^-1; after1000cycles, the SC was49.8F·g^-1，the ED and PD were46.8Wh·Kg^-1and905.7W·Kg^-1respectively. When the potential was increased to3.0V, the electrochemicalperformance was decreased obviously. We deduced that LiClO₄/acetonitrile maybehad some reactions at a high potential, which led the performance of SS reduction.At a potential range of [0,3.5V], the SS with NH602lithium ion electrolytecould carried out charge-discharge test successfully. The potential was higher than theLiClO₄/acetonitrile, and the SC, ED, PD were all heighten. At a current density of3mA·cm^-2, the SC was60.2F·g^-1，the ED was79.1Wh·Kg^-1，and the PD was11762.0W·Kg^-1; after1000cycles, the SC was56.3F·g^-1，the ED and PD were56.3Wh·Kg^-1and1170.7W·Kg^-1respectively. The reason may be that thecharge-discharge potential of NH602lithium ion electrolyte was high, and it couldincrease the ED; lithium ion could be rapidly dopde and dedoped, mass transfer ratewas fast and these may be the reasons that SS with NH602lithium ion electrolyte wassuitable for high power charge-discharge test.（3） Research on the effect of electrolyte on electrochemical performance ofasymmetric supercapacitorsTwo kinds of asymmetric supercapacitors （AS） with different electrolytes of1M LiClO₄/acetonitrile and NH602lithium ion electrolyte were fabricated respectively.Then they were measured by galvanostatic charge-discharge test. The result showedthat the AS with LiClO₄/acetonitrile could successfully carry out charge-dischargetest at a potential range of [0,2.7V], and the performance was stable. The SC of ASwith LiClO₄/acetonitrile was higher one time than the SC of SS. Because AS not onlyhad double electric layer capacitance, but also included faradic pseudocapacitancecaused by redox reaction of PANI. At a current density of3mA·cm^-2, the SC was118.0F·g^-1，the ED was100.0Wh·Kg^-1，and the PD was927.4W·Kg^-1; after1000cycles, the SC was95.1F·g^-1，the ED and PD were67.7Wh·Kg^-1and860.3W·Kg^-1respectively.The electrochemical performance of AS with NH602lithium ion electrolyte wasnot good. There was a inflection point on the charging curve at about2.5V, leading thecharging time was too long. And the charging time of each cycle was shorter andshorter with charge-discharge test. It indicated that energy charged into the AS above2.5V was consumed by some irreversible reactions caused by electrode surfacematerials. The electrode were tested by SEM, CV, EIS to discuss the reason. It may bethat the reversibility of PANI was bad in the NH602lithium ion electrolyte, and PANItiny particle was depolymerized and auto-polymerized, the surface became smooth,superficial area was descent, the SC was reduced. The resistance of PANI was toolarge in the NH602lithium ion electrolyte, and could reached up to several order ofmagnitudes, and this may be another reason that why electrochemical performance ofAS with NH602lithium ion electrolyte was not good...