Graphite anodic reduction

Other Metals. AH the sodium metal produced comes from electrolysis of sodium chloride melts in Downs ceUs. The ceU consists of a cylindrical steel cathode separated from the graphite anode by a perforated steel diaphragm. Lithium is also produced by electrolysis of the chloride in a process similar to that used for sodium. The other alkaH and alkaHne-earth metals can be electrowon from molten chlorides, but thermochemical reduction is preferred commercially. The rare earths can also be electrowon but only the mixture known as mischmetal is prepared in tonnage quantity by electrochemical means. In addition, beryIHum and boron are produced by electrolysis on a commercial scale in the order of a few hundred t/yr. Processes have been developed for electrowinning titanium, tantalum, and niobium from molten salts. These metals, however, are obtained as a powdery deposit which is not easily separated from the electrolyte so that further purification is required. 

The electrolytic processing of concentrated ore to form the metal depends on the specific chemical properties of the metallic compound. To produce aluminum about 2 to 6 percent of purified aluminum oxide is dissolved in ciyolite (sodium alumi-no-fliioride, Na AlF ) at about 960°C. The reduction of the alumina occurs at a carbon (graphite) anode ... 

In conclusion, it seems that solvents appropriate for lithium-ion batteries employing a graphite anode must have high solvation energy, high E°, and high /0 for reduction in order to slow the cointercalation of the solvated ion, and to enhance the formation of the SEI at the most positive potential (far from the Li/Li+ potential). 

Endo et al. investigated the reductive decomposition of various electrolytes on graphite anode materials by electron spin resonance (ESR). In all of the electrolyte compositions investigated, which included LiC104, LiBF4, and LiPFe as salts and PC, DMC, and other esters or ethers as solvents, the solvent-related radical species, which were considered to be the intermediates of reductive decomposition, were detected only after prolonged cathodic electrolysis. With the aid of molecular orbital calculation, they found that the reduction of salt anion species is very difficult, as indicated by their positive reduction enthalpy and that of free solvent (A/4 — 1 kcal mol ). However, the coordination of lithium ions with these solvents dramatically reduces the corresponding reduction enthalpy (A/ —10 kcal mol ) and renders the reaction thermodynamically favored. In other words, if no kinetic factors were to be considered, the SEI formed on carbonaceous anodes... 

To summarize, various models have been proposed to depict the formation of an SEI on a graphite anode, based on the common knowledge that the reductive... 

A sulfur analogue of EC, ethylene sulfite (ES), was proposed as an additive for PC-based electrolytes by Winter and co-workers,apparently because of its structural similarity to EC and its potential, under reductive conditions, to release SO2, a known additive that effectively suppresses PC decomposition. As the voltammetry in Figure 39 shows, ES in only 5% presence successfully eliminated the exfoliation of the graphite anode, whereas 10% SO2 failed. The irreversible process corresponding to the reduction of ES occurred at --"2.0 V, lower than that of SO2 by 0.80 V however, the quantity of charge associated was much lower. According to the authors, the above apparent gap between the reduction potentials of ES... 

The early patent disclosures have claimed the application of a wide spectrum of gas-evolving ingredients and phosphorus-based organic molecules as flame retarding additives in the electrolytes. Pyrocarbonates and phosphate esters were typical examples of such compounds. The former have a strong tendency to release CO2, which hopefully could serve as both flame suppressant and SEI formation additive, while the latter represent the major candidates that have been well-known to the polymer material and fireproofing industries.The electrochemical properties of these flame retardants in lithium ion environments were not described in these disclosures, but a close correlation was established between the low flammability and low reactivity toward metallic lithium electrodes for some of these compounds. Further research published later confirmed that any reduction of flammability almost always leads to an improvement in thermal stability on a graphitic anode or metal oxide cathode. 

While all these phosphate-based cosolvents were shown to be rather stable on various cathode materials, Xu et al. concentrated the evaluation effort on the reduction behavior of these flame retardants at the surface of graphitic anode materials. Figure 76 shows the results obtained with electrolytes containing high concentrations of TMP, TEP, and HMPN. 

Lithium metal is produced commercially by electrolysis of a fused eutectic mixture of hthium chloride-potassium chloride (45% LiCl) at 400 to 450°C. The eutectic mixture melts at 352°C in comparison to the pure LiCl melting at 606°C. Also, the eutectic melt is a superior electrolyte to LiCl melt. (Landolt, P.E. and C. A. Hampel. 1968. Lithium. In Encyclopedia of Chemical Elements.C. A. Hampel, Ed. Reinhold Book Corp. New York.) Electrolysis is carried out using graphite anodes and steel cathodes. Any sodium impurity in hthium chloride may be removed by vaporizing sodium under vacuum at elevated temperatures. All commercial processes nowadays are based on electrolytic recovery of the metal. Chemical reduction processes do not yield high purity-grade metal. Lithium can be stored indefinitely under airtight conditions. It usually is stored under mineral oil in metal drums. 

Electrolytic reduction of a lactose solution containing inorganic sulfite, between an amalgamated lead cathode and a graphite anode, is reported to give a 90% yield of lactitol with a 90% current-efficiency. ... 

The cyclization may be performed by anodic oxidation cyclodehydration of 2-thioamidopyridine to 2-phenyl-l,2,4-thiadiazolo[2,3-a]pyridinium perchlorate (259) occurs in excellent yield at a graphite anode. The process is reversed by the corresponding reduction at a platinum cathode.199... 

Reduction of several aliphatic and aromatic nitriles to the corresponding amines has also been reported. A palladium-coated nickel cathode, a carbon anode, and dilute hydrochloric acid have been used. A copper cathode, a graphite anode, and a promoter such as Raney nickel have been found satisfactory for the reduction of long-chain fatty nitriles. 

The electrolysis of narcotine in a diaphragmless cell with graphite anode and pre-polarized nickel cathode has been shown to give yields of 80% opianic acid and 55% cotarnine. Addition of potassium chloride prevents cathodic reduction of the narcotine. 

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