Graphite Aluminum‐ and Silicon Carbide‐Coated Current Collectors for Sodium‐Sulfur Cells

Abstract

The electrical performance and corrosion of current collectors made from graphite foil bonded to aluminum and from stainless steel protected by silicon carbide coating are compared to current collectors protected by chromium coatings. The testing is done in corrosion cells operated under dynamic conditions in Na2S~ melts at 350~ The cells are operated under both cathodic and anodic potentials of 100-300 mV measured with respect to carbon reference electrodes. The current collectors made from graphite foil, 127 tLm thick, bonded to aluminum have lowest total impedances (ohmic plus polarization) of 2.0 and 5.4 ~-cm 2 under cathodic and anodic potential of 300 mV. The corresponding values for silicon carbide coatings, 1.8-2.0 tLm thick, are 2.9 and 19.0 tl-cm 2, and, for chromium coatings -50 ~m thick, 3.2 and 10.7 gt-cm ~. No, or very little, corrosion is observed on the graphite/aluminum samples or on the silicon carbide-coated samples over a period of 2-3 months.

The Corrosion of Aluminum in Sodium Polysulfides and Sulfur at 350°C

“…The results presented here do not agree with those previously reported on the corrosion of a l u m i n u m in the positive electrode e n v i r o n m e n t s of the sodium/sulfur cell (1)(2)(3)(4)(5). There are two reasons for this.…”

“…(1) for a recent review]. Aluminum is one of the materials that many investigators have claimed to be compatible with the positive electrode environments (sodium polysulfide/sulfur) but this metal cannot be used as a current collector because its corrosion scale is an electronically insulating film of AI~S3 (1)(2)(3)(4)(5): In addition, the post-test analysis of sodium/sulfur cells constructed with an aluminum spacer in the container compression seal has shown extensive corrosive attack of the aluminum, with significant quantities of crystalline NaA1S2 dispersed throughout the polysulfide/graphite fiber matrix of the positive electrode (6). We have now completed a series of static corrosion tests of aluminum in various sodium polysulfides (i.e., Na2S3, Na2S4, Na2S,) and sulfur at 350~ The results clearly show that aluminum is not compatible with the discharged state of the positive electrode of the sodium/sulfur cell and that the corrosion product is only AI2Sa when the corrosion environment is sulfur.…”

Elucidating the Role of Defects for Electrochemical Intercalation in Sodium Vanadium Oxide

“…A linear dependency between the anodic and cathodic peak currents and the square root of the potential sweep rate indicates that the sodiation process is limited by solid state diffusion in the host material. If the rate-limiting step is sodium diffusion in the electrode and the charge transfer at the interface is fast enough, the relationship between the peak current and the CV scan rate can be expressed by the Randles− Sevcik equation 59 ν = × * I n AC D (2.69 10 ) p 5 3/2 Na Na 1/2 1/2 (2) where I p , n, A, and ν are the peak current, number of exchanged electrons, surface area of the electrode, and potential sweep rate; D Na is the sodium ion chemical diffusion coefficient and C Na * is the bulk concentration of sodium (0.011 mol cm −3 for Na x V 3 O 8 derived from the theoretical density of 3.55 g cm −3 ). 60 The average value of D Na into the Na x V 3 O 8 samples of deficient, ideal, and excess sodium stoichiometry is calculated to be 3.05, 1.53, and 1.89 × 10 −14 cm 2 s −1 , respectively.…”

“…1,2 The lower operating voltage of Na-ion cells results in enhanced stability of the nonaqueous electrolyte but also manifests itself in lower energy density. The majority of the proposed electrode materials for Na-ion battery show similar or slightly lower specific capacity and redox potential than when used in Li-ion cells.…”

Beyond Li-ion: electrode materials for sodium- and magnesium-ion batteries

“…NIBs are attractive because sodium resources are seemingly inexhaustible as well as ubiquitous, and therefore cost considerably less (by a factor of roughly 30-40 times) than lithium; additionally, sodium does not undergo an alloying reaction with aluminum at low voltage, as is the case with lithium, meaning that aluminum can replace copper as the anodic current collector which equates to an overall cell cost savings of ~2% [30,38,39]. The lower operating voltage of Na-ion cells results in enhanced stability of the nonaqueous electrolyte [30], but also manifests itself in lower energy density.…”