Carbonaceous cathodes

Fig. 7. First-order Raman spectra of (a) graphite, (b) inner core material containing nested nanotubes, (e) outer shell of carbonaceous cathode deposit (after ref. [24]).

The electro-Fenton (EF) process was the first proposed electrochemical AOP (EAOP) based on the continuous supply of H2O2 to an acidic aqueous solution from the two-electron reduction of injected oxygen gas at a carbonaceous cathode ... 

The construction of organic lithium cells is somewhat different from that of mercury and alkaline manganese cells. A lithium foil anode, a separator and a carbonaceous cathode are spirally wound together. This assembly is placed in a steel case, and the anode and eathode are eonnected with welded tabs to the case and top assembly. Since the electrolyte is non-aqueous, there is no hydrogen gas evolved during discharge. The... 

Lithium/carbon cells are typically made as coin cells. The lithium/carbon coin cell consists of several parts, including electrodes, separator, electrolyte and cell hardware. To construct a coin cell, we first must prepare each part separately. Successful cells will lead to meaningful results. The lithium/carbon coin cells used metallic lithium foil as the anode and a carbonaceous material as the cathode. The metallic lithium foil, with a thickness of 125 pm, was provided by Moli Energy (1990) Ltd.. Idie lithium foil is stored in a glove-box under an argon atmosphere to avoid oxidation. 

These anodes, like platinised Ti may be supplied in different forms e.g. rod, tube, mesh, wire, etc. They may be used for the cathodic protection of offshore structures, heat exchangers, or even pipelines as they can be installed in the soil surrounded by carbonaceous backfill, and are comparable in cost to platinised titanium. ... 

The anode may be installed in conventional groundbeds or be laid in close proximity to the cathode, e.g. parallel to a pipeline route. The anode may be buried either directly in soil or in carbonaceous backfill. The major applications for this material are tank protection, internal protection, mitigation of poor current distribution and hot spot protection, i.e. to supplement conventional cathodic protection systems and provide increased levels of cathodic protection in areas that exhibit low levels of protection. 

Soot deposited on the chamber wall contained mostly carbonaceous particles, where no MWNTs were contained. The deposits on the cathode consist of two portions the inside is black fragile core and the outside hard shell. The inside include MWNTs scad poljd ral graphitic nanoparticles. The outer-shell part ojnsisted of the crystd of graphite. 

Because of the similar potentials between fully lithiated graphite and lithium metal, it has been suggested that the chemical nature of the SEIs in both cases should be similar. On the other hand, it has also been realized that for carbonaceous anodes this formation process is not expected to start until the potential of this anode is cathodically polarized (the discharge process in Figure 11) to a certain level, because the intrinsic potentials of such anode materials are much higher than the reduction potential for most of the solvents and salts. Indeed, this potential polarization process causes one of the most fundamental differences between the SEI on lithium metal and that on a carbonaceous anode. For lithium metal, the SEI forms instantaneously upon its contact with electrolytes, and the reduction of electrolyte components should be indiscriminate to all species possible,while, on a carbonaceous anode, the formation of the SEI should be stepwise and preferential reduction of certain electrolyte components is possible. 

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... 

Compared with the research interest in the passivation of anodes, especially materials with carbonaceous origins, there have been relatively few studies dedicated to the understanding of the interface formed between electrolytes and cathode surfaces. A... 

When the poor anodic stability of DMC or EMC alone on a similar cathode surface is considered, the role of EC in stabilizing the solvent system becomes obvious. A conclusion that could be extracted from these studies is that the existence of EC not only renders the electrolyte system with superior cathodic stability by forming an effective SEI on the carbonaceous anode but also acts as a key component in forming a surface layer on the cathode surface that is of high breakdown potential. It is for its unique abilities at both electrodes that EC has become an indispensable cosolvent for the electrolyte used in lithium ion cells. 

A direct result of the work by Maleki et al. is the gradual shift of safety research from carbonaceous anode to cathode materials. In the following years, Dahn and co-workers used an improved ARC technique to conduct a series of systematic investigations on the reaction between electrolyte and cathode materials based on LiCo022 2 spinel... 

Irreversible Capacity. Because an SEI and surface film form on both the anode and cathode, a certain amount of electrolyte is permanently consumed. As has been shown in section 6, this irreversible process of SEI or surface layer formation is accompanied by the quantitative loss of lithium ions, which are immobilized in the form of insoluble salts such as Li20 or lithium alkyl carbonate. Since most lithium ion cells are built as cathode-limited in order to avoid the occurrence of lithium metal deposition on a carbonaceous anode at the end of charging, this consumption of the limited lithium ion source during the initial cycles results in permanent capacity loss of the cell. Eventually the cell energy density as well as the corresponding cost is compromised because of the irreversible capacities during the initial cycles. 

Overcharge tests were carried out in LiCo02 cathode half-cells that contained these additives, and a redox shuttle effect was observed between 4.20 and 4.30 V, close to the redox potentials of these additives. The same shuttling effect was observed even after 2 months of storage for these cells, indicating the stability and redox reversibility of these additives. A closer examination of the capacity retention revealed that 4-bromo-l,2-dimethoxybenzene seemed to have the best shuttle-voltage performance for the 4.0 V lithium cell used." The stability of these additives against reductive decomposition was also tested by the authors on metallic lithium as well as on carbonaceous anodes, and no deterioration was detected. 

Preferably, the new solvents are also expected to possess better stability or ability in interfacial chemistry on both anode and cathode materials so that the new electrolyte formulation can rely less on EC or they are expected to be less inflammable, as a major shortcoming of the linear carbonates is their low flash points (Tf) (Table 1). In the search for new solvents, fluorination has been adopted as a favorable approach to achieve improvements in these two aspects because the presence of C—F bonds in organic molecules is found to affect interfacial chemistry on carbonaceous anodes in a positive manner,and... 

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