The Passivity of 304 Stainless Steel in Propylene Carbonate Solutions

Abstract

The passivation behavior of 304 stainless steel in anhydrous propylene carbonate (PC) containing 0.5M LiAsF6 or 0.5M LiC104 was studied. The air-formed film on 304SS is stable up to the oxidation potential of PC (PCox). Scratch tests show that the bared 304SS surface repassivates in the anhydrous PC solutions of either electrolyte by chemisorption of PC molecules below PCox. In PC/0.5M LiAsF6 solutions, the 304SS is not passivated at potentials above PCox. In PC/0.5M LiC104 solutions the 304SS is passive at potentials 400-500 mV above PCox. This is attributed to the formation of a thin metastable perchlorate salt film or an adsorbed layer of perchlorate anions. When the perchlorate anions oxidize, the passivation becomes unstable and pitting occurs. Small (3-8 volume percent) additions of PC/0.5M LiC104 to PC/0.5M LiAsF6 solutions raises the passive range to the perch]orate oxidation potential. Small quantities of water, propylene glycol, and propylene oxide added to PC slightly improve the passive range of the 304 stainless steel.The increasing importance of lithium battery technology in a wide variety of applications has demonstrated a need for more reliable, longer-lived cells. Because of the reactivity of lithium in protic solvents such as water, aprotic organic solvents are used in most lithium batteries. Such solvents include propylene carbonate (PC), 1,2-dimethoxyethane (DME), 2-methyltetrahydrofuran (2-MeTHF), and more recently, mixtures of PC/2MeTHF and PC/DME (1). A wide variety of electrolytes have been used, but the most common are LiC104, LiA1C14, LiPF6, and more recently, LiAsF6 (2). The corrosive nature of these solutions is apparent based upon the fact that various types of stainless steels must often be used to encase such batteries. Passivity in aqueous solutions has been studied extensively. Comparatively little work has been done on the nature of the passive film and the breakdown of passivity on metals in nonaqueous solvents. The nature of the passive film on metal or alloy surfaces usually determines its protective and/or its corrosive behavior in aqueous environments and should establish its protective and corrosive nature in nonaqueous solvents.The purpose of this study was to investigate the passivity and the breakdown of passivity of 304 stainless steel in neutral anhydrous propylene carbonate (PC) containing either 0.5M LiAsF6 or 0.5M LiC104 electrolyte, and to determine the influence of common PC impurities. The influence of small additions of PC/LiC104 to PC/LiAsF6 solutions was also investigated and produced some surprising results. Previous work has studied the passive behavior of 99.995% iron in PC solutions (3-6) and 99.995% iron in PC-H20 mixtures (4, 7). Other examinations have investigated the passive behavior of 1018 carbon steel in PC solutions (5, 6) and mixed PC-H20 solutions (6), and nickel 200 in PC and mixed PC-H20 solvents (6).The mechanisms by which a metal can passivate can be classified into four types: (i) air-formed film, (ii) salt film formation, (iii) chemisorpti...

The Influence of Acidity, Chlorides and a High-Potential Quinone on the Corrosion of Hastelloy C-22 in Nonaqueous Solutions

“…This behavior is similar to that described for 304 stainless steel in anhydrous propylene carbonate. 16 Under strong anodic polarization (above 1.05 V vs Fc/Fc + ), the rise of current density is similar to that observed in transpassive dissolution in aqueous solutions, indicating that the initial passive film is dissolved, at least to some extent. Because there is no similar rise of current density on Pt, we can infer that the increase in current density exhibited on C-22 is truly due to the oxidation of the metal and not of the electrolyte or solvent.…”

“…Once the oxide was removed, repassivation could take place by either salt film formation or solvent adsorption, depending on the potential. 16 Of the myriad of species present in processes involving aprotic solvents, quinones deserve attention due to their redox-active behavior and their usefulness in biologic processes, as well as in the energy, pharmaceutical and chemical industries. 17 Although many studies have been dedicated to understanding the redox behavior of quinones, few studies have reported its effect on corrosion of metals.…”

Current Collectors for Positive Electrodes of Lithium-Based Batteries

“…19 However, SS304 has been shown to passivate readily in LiClO 4 /PC electrolytes up to 4.9 V vs Li/Li + , but in LiAsF 6 /PC only up to 4.1 V vs Li/Li + . 128 A common feature of SS and Fe is that EC considerably reduces the corrosion stability. This may be because the corrosion products are more soluble in EC-based solvents.…”

Passivation behavior of Type 304 stainless steel in a non-aqueous alkyl carbonate solution containing LiPF6 salt

“…In 1974, Heitz reviewed the state of the understanding of the corrosion of metals and alloys in organic solvents [8]. Kurger et al [9][10][11][12] observed that type 304 stainless steel readily passivated up to 4.9 V vs. Li /Li + in LiClO 4 /PC, even though the detailed passivation mechanism was not clarified.…”