Effects Of Some Organic Additives On Positive Electrolyte For All-vanadium Redox Flow Battery

Abstract:Preparation of electrolyte and effects of series of additives on positive electrolyte were studied in detail in this dissertation. Citric acid were used as reductant for preparing excellent property electrolyte of vanadium battey. Amino acids were first used as additives on positive electrolyte. And organics with different functional groups (-COOH、-OH and-NH2) were used as additives for studying the effects of functional groups on positive electrolyte. The main points can be summarized as following(1) Electrolyte was prepared by reduction with citric acid. The influence of additive content and reaction temperature on preparation were investigated and optimized. It indicates that optimum additive content wasn柠:nV2O5=1:2.9and the optimum reaction temperature was80℃. By comparing the electrochemical property of electrolyte prepared by electrolysis and reduction with optimum conditions, we found that electrolyte prepared by redution exhibited the best electrochemical performance.(2) Two amino acids (L-glutamate and L-arginine) have been individually used as an additive in a positive electrolyte containing2.0M VOSO4and3.0M H2SO4for all-vanadium redox flow batteries. The effects of each additive on the thermal stability and electrochemical properties of the positive electrolyte are investigated. The thermal stability tests show that the addition of L-glutamate to the positive electrolyte could delay the initiation of precipitation in the electrolyte. Cyclic voltammetry (CV) results suggest that the electrochemical reversibility of V(IV)/V(V) redox couple in the electrolyte has been improved by the addition of either L-glutamate or L-arginine. The diffusion coefficient of V(IV) has been increased. The discharge capacity loss (312.4mAh) of the cell with L-glutamate in the positive electrolyte is smaller compared to that (503.8mAh) of the cell with the pristine positive electrolyte. The columbic efficiency and energy efficiency of the cell are also increased by1.7%and2.0%, respectively, by the addition of L-glutamate in the positive electrolyte of the cell.(3) Succinic acid, malic acid and aspartic acid were investiged as additives for discussing the effects of functional groups on positive electrolyte. The results indicate that thermal stability of V(V) electrolyte were enhanced observably by adding malic acid and aspartic acid. Cyclicvoltammetry results suggest that the electrolyte with aspartic acid exhibited the best electrochemical property:highest reduction peak current (62.16mA), lowest peak current ratio (1.24) and maximal diffussion coefficient ((1.10～1.39)×10-6cm2/s). The charge-discharge test results show that the electrolyte with aspartic acid exhibited the smaller interval of the charge-discharge voltage plateau, longer charge-discharge time, highest average voltage efficiency (80.5%), energy efficiency (77.8%) and the lowest discharge capacity loss (206.6mAh). In conclusion, aspartic acid which contain-COOH and-NH2could effectively increase the thermal stability of V(V) electrolyte and improve the electrochemical and cell property.