Nonaqueous batteries

Nonaqueous solvents can form electrolyte solutions, using the appropriate electrolytes. The evaluation of nonaqueous solvents for electrochemical use is based on factors such as -> dielectric constant, -> dipole moment, - donor and acceptor number. Nonaqueous electrochemistry became an important subject in modern electrochemistry during the last three decades due to accelerated development in the field of Li and Li ion - batteries. Solutions based on ethers, esters, and alkyl carbonates with salts such as LiPF6, LiAsly, LiN(S02CF3)2, LiSOjCFs are apparently stable with lithium, its alloys, lithiated carbons, and lithiated transition metal oxides with red-ox activity up to 5 V (vs. Li/Li+). Thereby, they are widely used in Li and Li-ion batteries. Nonaqueous solvents (mostly ethers) are important in connection with other battery systems, such as magnesium batteries (see also -> nonaqueous electrochemistry). 

Although impedances at the anode-electrolyte and cathode-electrolyte interfaces are the limiting factor, ion transport within the bulk electrolyte is also an important consideration. Ion conductivity in nonaqueous solutions is much lower than in aqueous solutions in fact the part of the current carried by the lithium ions in the battery electrolytes is always less than half. A semiempirical rule has been observed the higher the bulk ion conductivity of the battery nonaqueous electrolyte, the more conductive the SEI formed on the electrode in this electrolyte [1]. In other words, more ionic conductivity desired in the SEI is heralded by higher lithium ion conductivity of the bulk electrol34 e. 

Lithium batteries must use nonaqueous electrolytes, usually combinations of solvents, for stabiUty because lithium reacts readily with water. Many of... 

Regarding the specific energy, i.e., the electric energy per mass, a major distinction can be made between today s aqueous and nonaqueous battery systems [15]. Apart from batteries for some special applications, there are... 

Although it is important that no water should exist in the cathode materials of nonaqueous batteries, the presence of a little water is unavoidable when Mn02 is used as the active material. It is believed that this water is bound in the crystal structure, and that it has no effect on the storage characteristics, as shown in Fig. 27, where the relationship of the MnO,... 

Most battery systems in which lithium is applied as anode material belong to the group using nonaqueous electrolytes, but there is one system that works with water serving as solvent and reactant as well. 

This section reports on the current state of knowledge on nonaqueous electrolytes for lithium batteries and lithium-ion batteries. The term electrolyte in the current text refers to an ion-conducting solution which consists of a solvent S and a salt, here generally a lithium salt. Often 1 1-salts of the LiX type are preferred for reasons given below only a few l 2-salts Li2X have attained some importance for batteries, and 1 3-salts Li3X are not in use. 

The ideal nonaqueous electrolyte for practical batteries would possess the following properties ... 

As to anodes, in most of the research work a generously dimensioned sheet of lithium metal has been used. Such an electrode is rather irreversible, but this is not noticed when a large excess of lithium is employed. Li-Al alloys and carbon materials inserting lithium cathodically during recharging can be used as anodes in nonaqueous solutions. Zinc has been used in polymer batteries with aqueous electrolyte (on the basis of polyaniline). 

Fignre 27.3 shows a typical spectroelectrochemical cell for in sitn XRD on battery electrode materials. The interior of the cell has a construction similar to a coin cell. It consists of a thin Al203-coated LiCo02 cathode on an aluminum foil current collector, a lithium foil anode, a microporous polypropylene separator, and a nonaqueous electrolyte (IMLiPFg in a 1 1 ethylene carbonate/dimethylcarbonate solvent). The cell had Mylar windows, an aluminum housing, and was hermetically sealed in a glove box. 

Another factor also contributed to the appearance of new concepts in electrochemistry in the second half of the twentieth century The development and broad apphca-tion of hthium batteries was a stimulus for numerous investigations of dilferent types of nonaqueous electrolytes (in particular, of sohd polymer electrolytes). These batteries also initiated investigations in the held of electrochemical intercalation processes. 

C without serious degradation, where nonaqueous and aqueous batteries have difficulties. 

Nonaqueous Liquid Electrolytes for Lithium-Based Rechargeable Batteries Kang Xu... 

In the nonaqueous organic solvent-based systems used for lithium batteries, the conductivities are of the order of 10 —10 S/cm k Compared to water, most organic solvents have a lower solvating power and a lower dielectric constant. This favors ion pair formation, even at low salt concentration. Ion pair formation lowers the conductivity as the ions are no longer free and bound to each other. Organic electrolytes show lower conductivities and much higher... 

Electrolytes are ubiquitous and indispensable in all electrochemical devices, and their basic function is independent of the much diversified chemistries and applications of these devices. In this sense, the role of electrolytes in electrolytic cells, capacitors, fuel cells, or batteries would remain the same to serve as the medium for the transfer of charges, which are in the form of ions, between a pair of electrodes. The vast majority of the electrolytes are electrolytic solution-types that consist of salts (also called electrolyte solutes ) dissolved in solvents, either water (aqueous) or organic molecules (nonaqueous), and are in a liquid state in the service-temperature range. [Although nonaqueous has been used overwhelmingly in the literature, aprotic would be a more precise term. Either anhydrous ammonia or ethanol qualifies as a nonaqueous solvent but is unstable with lithium because of the active protons. Nevertheless, this review will conform to the convention and use nonaqueous in place of aprotic .]... 

The concept of rocking-chair lithium batteries was confirmed experimentally by using lithiated oxides (LieFezOs, LiW02) as interaction anodes and other oxides (WO3, TiS2, V2O5) as cathodes in nonaqueous... 

An ideal electrolyte solute for ambient rechargeable lithium batteries should meet the following minimal requirements (1) It should be able to completely dissolve and dissociate in the nonaqueous media, and the solvated ions (especially lithium cation) should be able to move in the media with high mobility. (2) The anion should be stable against oxidative decomposition at the cathode. (3) The anion should be inert to electrolyte solvents. (4) Both the anion and the cation should remain inert toward the other cell components such as separator, electrode substrate. 

Like LiAsFe, LiBF4 is a salt based on an inorganic superacid anion and has moderate ion conductivity in nonaqueous solvents (Table 3). It was out of favor in the early days of lithium battery research because the ether-based electrolytes containing it were found to result in poor lithium cycling efficiencies, which decayed rapidly with cycle number. ° The reactivity of LiBF4 with lithium was suspected as discoloration occurred with time or heating. 

Stability limits for some nonaqueous solvents commonly used in lithium-based battery research. Despite the inconsistency created by the varying measurement conditions, these data express a general trend that we have discussed in section 2 that is, carbonates and esters are more anodically stable, while ethers are more resistant to cathodic decompositions. 

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