Lithium electrochemical potential

Main electrode features, which determine the energy density of an electrochemical storage cell, are the volumetric or specific capacity, i.e., the electric charge that electrodes can store per unit volume or weight, respectively, and the electrochemical potential they produce. Considering thermodynamic reasons, lithium, as being the most electropositive (-3.04 V vs. SHE) metal, is exceptional for use as... 

The Li-Ion system was developed to eliminate problems of lithium metal deposition. On charge, lithium metal electrodes deposit moss-like or dendrite-like metallic lithium on the surface of the metal anode. Once such metallic lithium is deposited, the battery is vulnerable to internal shorting, which may cause dangerous thermal run away. The use of carbonaceous material as the anode active material can completely prevent such dangerous phenomenon. Carbon materials can intercalate lithium into their structure (up to LiCe). The intercalation reaction is very reversible and the intercalated carbons have a potential about 50mV from the lithium metal potential. As a result, no lithium metal is found in the Li-Ion cell. The electrochemical reactions at the surface insert the lithium atoms formed at the electrode surface directly into the carbon anode matrix (Li insertion). There is no lithium metal, only lithium ions in the cell (this is the reason why Li-Ion batteries are named). Therefore, carbonaceous material is the key material for Li-Ion batteries. Carbonaceous anode materials are the key to their ever-increasing capacity. No other proposed anode material has proven to perform as well. The carbon materials have demonstrated lower initial irreversible capacities, higher cycle-ability and faster mobility of Li in the solid phase. 

Table 4 lists selected electrochemical stability data for various lithium salt anions that are commonly used in lithium-based electrolytes, with the measurement approaches indicated. Although it has been known that the reduction of anions does occur, sometimes at high potentials, the corresponding processes are usually sluggish and a definite potential for such reductions is often hard to determine. The reduction of solvents, occurring simultaneously with that of anions on the electrode, further complicates the interpretation efforts. For this reason, only the anodic stability of salt anions is of interest, while the cathodic limit of the salt in most cases is set by the reduction of its cation (i.e., lithium deposition potential). 

It was noticed that in neutral MEIC-AlCl3-NaCl melts the efficiency of sodium and lithium deposition is zero, because the sodium and lithium deposition potentials are not inside the electrochemical window. But if the above-mentioned... 

As lithium combines the highest electrochemical potential of all metals with a low equivalent weight, it is a very attractive construction material for anodes in electrochemical cells as high-energy/density... 

The SCC behavior of cold worked AISI type 316L (UNS S31603) stainless steel in a concentrated lithium salt solution at elevated temperature was investigated by Zheng and Bogaerts [138]. Using the SSRT technique, SCC experiments were performed under controlled electrochemical potential on 20% and 40% cold worked materials in a solution... 

Fig. 16.1 Electrochemical potential of cathode material for lithium-ion battery...

XRR has been applied to the study of EEIs on several systems [201-205]. The technique was found to be sensitive not only to the formation of reaction layers but also to mass loss at the electrode surface due to processes of corrosion (dissolution) [201]. Of particular interest is the application of high energy synchrotron beams as sources, as their deep penetration capabilities enables the design of operando cells (Fig. 7.10a) [203], Therefore, uncertainty due to equilibration in the absence of an electrochemical potential is eliminated. The structural and chemical stability of EEIs during the lithium insertion/extraction processes have thus been evaluated (Fig. 7.10b) [201-204]. The dependence of these irreversible reactions on the crystal facet of the electrode material forming the EEI was established. It was found that electrolyte decomposition processes were coupled with the redox process occurring in the bulk of the electrode, which is a critical piece of information when designing materials that bypass such layer formation. 

The value for x is generally between 0 and 1. Carbons intercalated with Li" can have electrochemical potentials within tens of millivolts of the lithium metal potential when fully charged. 

The practical electrochemical parameters (actual cell capacity, cell voltage, etc.) are strongly related to the theoretical thermodynamic calcnlalions and are usually diminished by a certain factor because of the occurrence of various real-life usage losses. The most important theoretical properties of battery materials (electrochemical potential of the cell, cell s theoretical capacity, and energy) are derived from thermodynamics of the electrode reactions in lithium-ion cell (Table 1.1). A comprehensive, in-depth discussion of thermodynamics of the processes occurring in a lithium-ion cell can be found elsewhere [4]. Some of the most crucial formulas are Usted below. 

The electrochemical potential of the couple H2O/O2 is higher than that of the negative materials used for lithium-ion batteries. For this reason, these batteries are reactive to water and decompose in the presence of water or humidity. 

Lithium s very low electrochemical potential renders it a very powerful reducing agent. Lithium will react with any other component in its vicinity. On contact with the nitrogen in the air, it forms a layer of nitride by way of the following reaction ... 

Metals are important construction materials, which are classified according to their properties as light or heavy metals (density lower/higher than 4.5 g cm" ), and precious, ferrous, or nonferrous metals. An evaluation of metal corrosion resistance can be derived from the electrochemical potential series. This is valid for metals introduced under standard conditions into an aqueous solution of their ions. Gold is situated at the electronegative end and lithium at the electropositive one. All the other metals, e.g., aluminum, zinc, iron, copper, silver, etc., are situated in-between. Furthermore, with respect to corrosion resistance, the tendency to form passivating layers is important. These are generally thin oxide layers which confer the metals with an apparently more noble position in the potential series than they really have. 

A number of factors have to be considered in the choice of the intercalation compound, such as reversibility of the intercalation reaction, cell voltage, variation of the voltage with the state of charge, and availability and cost of the compound. Table 34.5 lists the key requirements for the intercalation materials and Table 34.6 presents some of the characteristics of the intercalation and other compounds that have been used in lithium rechargeable batteries. The electrochemical potentials of several lithium intercalation compounds versus those of lithium, metal and the variation of voltage with the amount of intercalation are shown in Fig. 34.2. 

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