Chemical Reactions in Lithium Sulfur Dioxide Cells Discharged at High Rates and Temperatures

Abstract

The discharge capacity of Li/SO2 cells was examined at high current and temperatures. D cells rated at 8 Ah delivered over 7 Ah at 5A current and 55~ while cells discharged at 72~ gave 7 Ah at 3A. The cells were analyzed for residual lithium and sulfur dioxide. Spent cathodes were analyzed by infrared spectroscopy. A parasitic reaction was found in which Li2S20~ and S were formed, presumably by reaction of Li2S204 with SO2. This reaction became noticeable only under extreme combination of high rate and temperature.Lithium/SO~ cells are useful power sources for devices requiring high drain pertormance at low temperatures. Such cells generally are of a jelly roll design with layers of lithium toil, separator, and porous carbon cathode. The electrodes are surrounded by a highly conductive nonaqueous electrolyte consisting of an organic solvent (usually acetonitrile), a salt (usually lithium bromide), and sulfur dioxide, which serves as a soluble cathode material (1). In the course of cell discharge the lithium anode is oxidized, and the SO2 soluble cathode is reduced. The discharge product, identified as lithium dithionite (2), precipitates in the porous cathode and eventually may passivate it. Such cells have open-circuit voltages near 3V and discharge at around 2.8V, delivering 140-150 Wh/lb over the cells' life (3, 4). Typical SO~ D cells have short-circuit currents of over 100A and can deliver 30A pulses at specific powers of over 300 W/lb. In the course of discharging cells at elevated temperatures, it was observed that some cells delivered less than the usual capacity. We discharged a number of LO25SX and LO26SX D-type SO2 cells at different rates and temperatures to determine the extent and magnitude of this decline in capacity. We used infrared spectroscopy and specific chemical analysis to identify products of the cells. We report the results here. ExperimentalThe LO26SX, a hermetically sealed spirally wound D cell, was selected .as a test vehicle for this study. The LO26SX is distinguished by its balanced cell chemistry in which the ratio of Li metal and SO2 soluble cathode is near unity. This particular cell is rated at 8 Ah at 267 mA at 25~ Capacities were calculated to a 2V cutoff and cells used for chemical analyses were not discharged below 2V. Cells were discharged at 21 ~ 55 ~ and 72~ on selected loads, as well as at constant currents, with data collection either by a Linseis LD-12 recorder or an HP 1000 computerized data-acquisition system.Cells which were used for chemical analysis were placed in a specially made stainless steel bomb and punctured. The volatile acetonitrlle and SO2 Were

A Spectroscopic Investigation of Lithium Dithionite and the Discharge Products of a Li / SO 2 Cell

“…A strong IR band is observed at 968 cm-k Recently, a similar band at 970 cm -~ was reported by Bowden et al, which they attributed to be ditriionate based on a comparison with IR spectra of Na2S206 (19). However, a sample of Na2S206, analyzed at >99% purity by standard methods, exhibited a band at 998 cm-L We attributed the band at 968 cm -i to the presence of Li2SO3.…”

“…However, the absence of the strong bands in the ~1060 cm -i region is an argument against the presence of metabisulfite. Since acceptance of this manuscript, a recent paper has reported that metabisulfite is present in cells discharged at 72~ (24).…”

High-efficiency and high-power rechargeable lithium–sulfur dioxide batteries exploiting conventional carbonate-based electrolytes

“…This theoretical tendency is in accordance with the previous experimental findings that the chemical equilibrium constant of dimerization reaction to dithionite ion has a positive correlation with the dielectric constant of organic solvent media 40 . It is noteworthy that the previously proposed discharge mechanism of the primary Li-SO 2 battery was based on the formation of S 2 O 4 2− rather than SO 2 − or LiSO 2 (refs 32 , 38 ). It is our speculation that this finding is most likely due to the use of an acetonitrile-based electrolyte in most primary Li-SO 2 batteries 8 9 10 32 , which has a high dielectric constant ( ɛ ∼35.9) 41 42 comparable to that of EC/DMC.…”

“…It is noteworthy that the previously proposed discharge mechanism of the primary Li-SO 2 battery was based on the formation of S 2 O 4 2− rather than SO 2 − or LiSO 2 (refs 32 , 38 ). It is our speculation that this finding is most likely due to the use of an acetonitrile-based electrolyte in most primary Li-SO 2 batteries 8 9 10 32 , which has a high dielectric constant ( ɛ ∼35.9) 41 42 comparable to that of EC/DMC. Although the overall processes to attain the final product of Li 2 S 2 O 4 are thermodynamically favourable with identical energy change of overall reactions in both electrolytes as shown in Supplementary Table 1 , it should be noted that the energy profiles along the elementary reaction pathways for Li-SO 2 batteries were significantly different depending on the type of electrolyte.…”

“…The basic principle of Li-SO 2 battery operation is based on the simple electrochemical reaction between Li and SO 2 gas, whose general discharge reaction is 31 32 :…”