Sulfur-based Cathode

FIGURE 34.31 Ragone plot for 0.8 Ah thin-film lithium battery with sulfur-based cathode material. (From Ref. 56.)... 

Masset P, Guidotti RA (2008) Thermal activated ( thermal ) battery technology Part Illb. Sulfur and oxide-based cathode materials. J Power Sources 178 456-466 Janata J (1992) Chemical sensors. Anal Chem 64 196-219... 

The liquid (sulfur-based compounds) and sohd sulfur cathodes (items 6 and 7) do not develop surface chemistry that can be separated from their main electrochemical redox reactions. Hence, when the reduction of sulfur SO2 or SOCI2 produces insoluble species such as LiCl, LijS, and LijO, they precipitate on the current collector [9]. When formed, LijS can be reoxidized, up to elemental sulfur, via various LLS intermediate compounds [10]. Hence, the current collector, which may be aluminum (Al) plus carbon in the case of sulfur cathodes or carbon in the case of SOCI2 cathodes, does not develop intrinsic surface chemistry beyond the precipitation of the reduction products of the active mass. 

The polymer electrolyte lithium batteries contain aU solid-state components lithium as the anode material, a thin polymer film as a solid electrolyte and separator, and a transition metal chalcogenide or oxide, or a sulfur-based polymer as tbe cathode material. These features offer the potential for improved safety because of tbe reduced activity of lithium with the solid electrolyte, flexibility in design as tbe cell can be fabricated in various sizes and shapes, and high energy density. 

The early batteries used polyethylene oxide (PEO)-based electrolytes containing a Uthium salt, which have an appreciable conductivity at about 100°C but low conductivity at room temperature. Later new polymeric electrolyte materials, sucb as PEO copolymers, PEO blends, plasticized PEO electrolytes, and gelled electrolytes, with better conductivity were developed. Some of the cathode materials investigated for these batteries are TiS2, VO V2O5, Li Co02 and sulfur-based polymers. 

In traditional Li-S liquid cells, in order to enhance electronic conductivity of sulfur and its discharge products, carhon materials with/without conducting polymers are always used. In the meantime, hquid electrolytes supply the ionic conductivity for sulfur electrode during cycling [26, 27]. However, use of liquid electrolytes always leads to the polysulfide shuttle, which is a tough challenge associated with Li-S liquid cells [28]. In this section, we look back on the most recent advances in electrochemical performance of traditional Li-S cells from different cell components, i.e., the suUur-based cathode, the hthium anode, and the hquid electrolyte. 

Traditionally electrolytes provide effective Li-ion transport between electrodes and work as a charge-transfer medium within sulfur-containing cathodes. Special requirements for electrolytes in Li-S cells include low viscosity and low solubility of sulfur species. A common Li-S electrolyte consists of a Li salt such as lithium triflate (LiCFaSOa), LiTFSl, LiPFs, and LiC104, and a matrix of one or two organic solvents. Based on liquid electrolytes used in Li-S cells, here we divide and discuss them into four categories (1) ether-based electrolytes, (2) carbonate-based electrolytes, (3) ionic liquid-based electrolytes, and (4) other new Uquid systems. 

The Li3PS4+5 cathode showed an initial discharge capacity of 1272 mAh (based on the incorporated sulfur content) (Fig. 15b) with 100 % coulombic efficiency after a few initial cycles at room temperature. Even better cycling performance was observed at 60 °C. The initial capacity was >1400 mAh g, and a high capacity of 1200 mAh g was maintained after 300 cycles. The increased ionic conductivity of the sulfur-rich cathode and the elimination of the polysuffide shuttle are responsible for improved cycling performance. 

Hard plating is noted for its excellent hardness, wear resistance, and low coefficient of friction. Decorative plating retains its brilliance because air exposure immediately forms a thin, invisible protective oxide film. The chromium is not appHed directiy to the surface of the base metal but rather over a nickel (see Nickel and nickel alloys) plate, which in turn is laid over a copper (qv) plate. Because the chromium plate is not free of cracks, pores, and similar imperfections, the intermediate nickel layer must provide the basic protection. Indeed, optimum performance is obtained when a controlled but high density (40—80 microcrack intersections per linear millimeter) of microcracks is achieved in the chromium lea ding to reduced local galvanic current density at the imperfections and increased cathode polarization. A duplex nickel layer containing small amounts of sulfur is generally used. In addition to... 

The horizontal surfaces should be coated because there is residual water in the ballast and there are water-oil mixtures in the crude oil tanks when ships travel empty and these can cause severe corrosion attack. In the lower part of the tank, up to about 1.5 m from the base, a combination of coating and cathodic protection with special anodes is chosen. Basically the anodes could take over the exclusive protection in this area, but with empty ballast tanks containing residual water or empty crude oil tanks with aggressive oil-water mixtures containing sulfur compounds, they do not prevent corrosion. 

The formation of colloidal sulfur occurring in the aqueous, either alkaline or acidic, solutions comprises a serious drawback for the deposits quality. Saloniemi et al. [206] attempted to circumvent this problem and to avoid also the use of a lead substrate needed in the case of anodic formation, by devising a cyclic electrochemical technique including alternate cathodic and anodic reactions. Their method was based on fast cycling of the substrate (TO/glass) potential in an alkaline (pH 8.5) solution of sodium sulfide, Pb(II), and EDTA, between two values with a symmetric triangle wave shape. At cathodic potentials, Pb(EDTA)2 reduced to Pb, and at anodic potentials Pb reoxidized and reacted with sulfide instead of EDTA or hydroxide ions. Films electrodeposited in the optimized potential region were stoichiometric and with a random polycrystalline RS structure. The authors noticed that cyclic deposition also occurs from an acidic solution, but the problem of colloidal sulfur formation remains. 

In applications where Nafion is not suitable, at temperatures above 200 °C with feed gas heavily contaminated with CO and sulfur species, a phosphoric acid fuel cell (PAFC)-based concentrator has been effective [15]. Treating the gas shown in Table 1, a H2 product containing 0.2% CO, 0.5%CO2 and only 6 ppm H2S was produced. The anode electrode was formed from a catalyst consisting basically of Pt-alloy mixed with 50% PTFE on a support of Vulcan XC-72 carbon. The cathode was... 

The electrolysis in aqueous sulfuric acid with methanol as a cosolvent was perfomed in a filterpress membrane cell stack developed at Reilly and Tar Chemicals. Because of the low current density of the process, a cathode based on a bed of lead shot was used. A planar PbOa anode was used. The organic yield was 93% with approximately 1% of a dimer. The costs of the electrochemical conversion were estimated as one-half of the catalytic hydrogenation on a similar scale. 

Table VII gives the m.p. of other alumohalides and their mixed systems. For example, low-melting electrolytes based on AlCla MCl chloraluminates, where M is Li, Na, K, have been considered (87), and cells with A1 anode and various cathodes, both inorganic and organic, were tested. The sulfur cathode seems to be the most suitable, although complex chlorides, fluorides and sulfides show possibilities. An experimental Al/S cell is described in detail in (88). The reaction 2A1 + 3S = AI2S3 provides a TED of 1275 Wh/kg at 200°. It is viewed only as a primary battery, however at the present time (88).

---