Improvement On The Properties Of Electrolytes In All Vanadium Redox Flow Battery

With the rapid and sustained development of China’s economy,the improvement of productivity needs more and more non-renewable energy,such as coal,oil,etc.Given excessive use and non-renewable energy reserves is limited,now,these energy face a dwindling trend.Therefore,the development of renewable energy sources such as wind,solar is imminent.In order to develop these new energy,we must solve the discrete problem in power supply,in a word,in order to develop low-cost and continuous power supply,we need study better erengy storage technology.The all vanadium flow battery（hereinafter referred to as VRB）can be applied to renewable energy power generation,energy storage terminal grid and military bases because of its advantages:long life,high efficiency,low self-discharge,flexible equipment,location freedom,and so on.A solution method is used to prepare V⁴⁺ ion solution in this paper,while a electrochemical method is adopted to prepare V²⁺,V³⁺and V5+ ion solutions,respectively.These three vanadium ion solutions’s preparation take V⁴⁺ ion solution solution as raw material.Ptentiometric titration,first derivative method and second derivative method are employed to analyze the compositions of the electrolytes and different valence vanadium ion solutions’s concentrations.The UV-Vis spectrometry,Cyclic voltammetry and impedance spectroscopy method are used to study the electrochemical properties of the electrolytes.The experimental results show that the four vanadium electrolytes have been prepared successfully and their concentrations are 1.95mol·L-1 V²⁺,1.95mol-L-1 V³⁺,2.00mo1-L-1 V⁴⁺and 2.25mol·L-1 V5+,respectively.The cyclic voltammetry tests show that the oxidations of V²⁺,V³⁺ and V⁴⁺ are all quasi reversible process and mainly controlled by diffusion process,while the reduction of V⁴⁺ to V²⁺ is doubly controlled by diffusion process and electrode reaction process.Based on the above studies,this paper adopts the method of adding additives SnCl₄/SnCl₂ into the vanadium battery electrolyte to optimize and study the property of the electrolyte.Namely,in order to improve the electrolyte performance,SnCl₄ and SnCl₂ are regarded as oxidant additives which are firstly added to the electrolyte,and cyclic voltammetry and impedance spectroscopy method are used to study the results.The experiment results show that SnCl₂ and SnCl₄ have better optimization effects on the positive electrolyte and increase the battery efficiency.The reversibility of electrolyte redox reaction is enhanced with the increase of SnCl₂ and SnCl₄’s amount in positive electrolyte.At the same time,the redox reaction’s peak current increased obviously,namely the battery efficiency improved significantly.In addition,the results also show that SnCl₂ and SnCl₄ are useless to improve the property of the negative electrolyte and increase the battery efficiency.