Anode, alkali metals

It is now well established that in lithium batteries (including lithium-ion batteries) containing either liquid or polymer electrolytes, the anode is always covered by a passivating layer called the SEI. However, the chemical and electrochemical formation reactions and properties of this layer are as yet not well understood. In this section we discuss the electrode surface and SEI characterizations, film formation reactions (chemical and electrochemical), and other phenomena taking place at the lithium or lithium-alloy anode, and at the Li. C6 anode/electrolyte interface in both liquid and polymer-electrolyte batteries. We focus on the lithium anode but the theoretical considerations are common to all alkali-metal anodes. We address also the initial electrochemical formation steps of the SEI, the role of the solvated-electron rate constant in the selection of SEI-building materials (precursors), and the correlation between SEI properties and battery quality and performance. 

The formation of an anodic film on alkali metal anodes is mentioned in (129b). If it can be confirmed that Li is not unique in its reaction with water, as it is claimed in (123-124), then Na may also develop such a film in contact with H2O or non-aqueous liquids and so be protected. Design variations in Na-H20 primary batteries are described (130-132). 

Prospects for TR Electrolyte SBs. In view of the harmful effects often cited in the literature of even small traces of water on the operation of non-aqueous batteries with alkali metal anodes, it might be supposed that electrolytes of the TR composition cannot be applied in such batteries. This same idea may dominate when molten salt SBs are considered. Such a general conclusion cannot be justified. A dilute solution of water in a salt has the structure either of this salt proper or its adjacent hydrate, and the energy, properties and reactions of this water are quite different from those of pure water or of dilute solutions of various compounds in it. On the other hand, a small amount of water in the electrolyte system will decrease its melting point and increase its conductivity. Mixtures of water with such liquids as some alcohols or dioxane and other aprotic and even proton-forming substances, may open new prospects for... 

L. P. Klemann, G. H. Newman, U.S. Patent 4,060,674, 1977. Alkali metal anode-containing cells having electrolytes of oiganometallic-alkali metal salts and oiganic solvents. 

Practical primary or secondary alkali-metal or alkaline-earth batteries can be made only if the dissolution of the anode by reactions (16.1) and (16.2) (and by other corrosion reactions) can be stopped. Since attacks both the electrolyte and the cathode, the electrolyte must be designed to contain at least one material that reacts rapidly with lithium (or with the alkali-metal anode) to form an insoluble SEI. On inert electrodes, the SEI is formed by reduction of the electrolyte. This type of electrode (completely covered by SEI), was named [1, 2] the SEI electrode. ... 

Chlorate. Conversion to metal anodes has also taken place in this process. Sodium hydroxide, which is formed at the cathode, reacts to form the sodium chlorate product (see Alkali and chlorine products). 

The organization of the Handbook of Battery Materials is simple, dividing between aqueous electrolyte batteries and alkali metal batteries and further in anodes, cathodes, electrolytes and separators. There are also three more general chapters about thermodynamics and mechanistics of electrode reactions, practical batteries and the global competition of primary and secondary batteries. 

Tellurium has been tested as a cathode material for use in conjunction with an anode made of alkali metal, primarily lithium, in power sources with a high specific energy and power [99], The theoretical specific energy for Li/Te pair is 612 Wh kg High-temperature (470 °C) cells with Li, Te, and eutectic (LiF-LiCl-Lil) electrolyte in the molten state, or with more convenient, albeit more resistive, paste-type electrolytes, have been tested in the laboratory. Similar layouts have been proposed for utilizing the Li/Se pair (theoretic cal specific energy 1,210 W h kg ) with the cell ingredients in the molten state (365 C) or with paste electrolyte at a lower temperature. 

M. Faraday was the first to observe an electrocatalytic process, in 1834, when he discovered that a new compound, ethane, is formed in the electrolysis of alkali metal acetates (this is probably the first example of electrochemical synthesis). This process was later named the Kolbe reaction, as Kolbe discovered in 1849 that this is a general phenomenon for fatty acids (except for formic acid) and their salts at higher concentrations. If these electrolytes are electrolysed with a platinum or irridium anode, oxygen evolution ceases in the potential interval between +2.1 and +2.2 V and a hydrocarbon is formed according to the equation... 

In an individual molten carbamide, the electrode processes are feebly marked at melt decomposition potentials because of its low electrical conductivity. Both electrode processes are accompanied by gas evolution (NH3, CO, C02, N2) and NH2CN (approximately) is formed in melt. In eutectic carbamide-chloride melts electrode processes take place mainly independently of each other. The chlorine must evolve at the anode during the electrolysis of carbamide - alkali metal and ammonium chloride melts, which were revealed in the electrolysis of the carbamide-KCl melt. But in the case of simultaneous oxidation of carbamide and NH4CI, however, a new compound containing N-Cl bond has been found in anode gases instead of chlorine. It is difficult to fully identify this compound by the experimental methods employed in the present work, but it can be definitely stated that... 

At high anodic potentials Prussian blue converts to its fully oxidized form as is clearly seen in cyclic voltammograms due to the presence of the corresponding set of peaks (Fig. 13.2). The fully oxidized redox state is denoted as Berlin green or in some cases as Prussian yellow . Since the presence of alkali metal ions is doubtful in the Prussian blue redox state, the most probable mechanism for charge compensation in Berlin green/Prussian blue redox activity is the entrapment of anions in the course of oxidative reaction. The complete equation is ... 

In the chlor-alkali industry titanium brings its properties to application as a material in activated metal anodes. In fact this is the major use of titanium in the chlor-alkali industry. 

Photoemissive tubes are necessary for work in the ultraviolet range and they show greater sensitivity and precision than photoelectric cells. A simple photo-emissive tube consists of two electrodes in a vacuum. A silver cathode coated with an alkali metal is maintained at a potential difference of about 100 V from the anode, which is a plain silver wire and serves to collect the electrons (Figure 2.26(a)). 

Table 10 Anodic shifts (mV) in the formal reduction potentials of [50]—[53] upon addition of alkali metal cations.

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