Functional electrolyte

Although reports following the initial marketing of Sony Corporation s batteries focused not only on metallic lithium anodes and graphite anodes but also on the solid electrolyte interphase (SEI), which forms on the anode as a result of electrolyte decomposition, intentional control of SEI was not considered in sufficient depth. The concept of SEI was advocated by Peled from Tel-Aviv University and Aurbach from Bar-Ilan University [8-10]. Nevertheless, upon entering the industry in 1997, Ube Industries, Ltd. started adding small amounts of additives to the electrolyte, which allowed for the undesirable thick SEI to be controlled by deliberately causing additive decomposition in order to form a controlled thin layer (CTL). 

In 1999, the concept of functional electrolytes was coined and developed [ 11,12] on the basis of the idea of intentionally controlling thick SEI and improving 

The electrochemical properties and cyclabiLity of the additives have been investigated. The additives are foimd to decompose on the cathode to form a very thin film. This resulting novel-t) e thin surface film has been addressed as an electroconductive membrane 

It has been concluded that these additives, which were formerly known as overcharge protection proofs, contribute to improve the cathode cyclabihty by forming very thin cathode surface layer in the case of sUght amount of addition (33). 

In contrast, in the case of 2% addition, an oxidative decomposition of the additives progresses as the cycle proceeds, which leads to an battery capacity fading, because the grown cathode film becomes thick with a high Li+ ion resistance. 

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In the case of molten salts, the functional electrolytes are generally oxides or halides. As examples of the use of oxides, mention may be made of the electrowinning processes for aluminum, tantalum, molybdenum, tungsten, and some of the rare earth metals. The appropriate oxides, dissolved in halide melts, act as the sources of the respective metals intended to be deposited cathodically. Halides are used as functional electrolytes for almost all other metals. In principle, all halides can be used, but in practice only fluorides and chlorides are used. Bromides and iodides are thermally unstable and are relatively expensive. Fluorides are ideally suited because of their stability and low volatility, their drawbacks pertain to the difficulty in obtaining them in forms free from oxygenated ions, and to their poor solubility in water. It is a truism that aqueous solubility makes the post-electrolysis separation of the electrodeposit from the electrolyte easy because the electrolyte can be leached away. The drawback associated with fluorides due to their poor solubility can, to a large extent, be overcome by using double fluorides instead of simple fluorides. Chlorides are widely used in electrodeposition because they are readily available in a pure form and... 

The auxiliary electrolyte is generally an alkali metal or an alkaline earth metal halide or a mixture of these. Such halides have high decomposition potentials, relatively low vapor pressures at the operating bath temperatures, good electrolytic conductivities, and high solubilities for metal salts, or in other words, for the functional component of the electrolyte that acts as the source of the metal in the electrolytic process. Between the alkali metal halides and the alkaline earth metal halides, the former are preferred because the latter are difficult to obtain in a pure anhydrous state. In situations where a metal oxide is used as the functional electrolyte, fluorides are preferable as auxiliary electrolytes because they have high solubilities for oxide compounds. The physical properties of some of the salts used as electrolytes are given in Table 6.17. 

Therapeutic Function Electrolyte replenisher Chemical Name D-Gluconic acid, monosodium salt... 

Diuretics 1 responsiveness owing to decline in renal function Enhanced monitoring of renal function, electrolytes... 

When starting digoxin therapy, it is important to obtain baseline electrolyte levels and renal function. Electrolyte... 

Most macromolecules when dissolved in salt solutions acquire charges that are shielded by an atmosphere of counterions. This ion atmosphere affects the diffusion coefficient of the macromolecule and hence the light-scattering time-correlation function. Electrolyte solutions are discussed in Chapters 9 and 13. Recent measurements of diffusion coefficients have been made by several groups. Lee and Schurr (1974) have studied poly-L-lysine-HBr. Schleich and Yeh (1973) have performed similar studies on poly-L-proline. Raj and Flygare (1974) have studied bovine serum albumin (BSA) and find that at high ionic strength and low pH the diffusion constant decreases. This they attribute to the expansion of the molecule. 

H. Yoshitake, Functional Electrolyte in Lithium Ion Batteries (in Japanese), M.Yoshio, A. Kozawa, Eds., Nikkan Kougyou Shinbunsha, Japein, 2000, pp. 73-82... 

Most of the liquid electrolytes used in the commercial lithium-ion cells are the nonaqueous solutions, in which roughly 1 mol (tar (= M) of lithium hexafluoro-phosphate (LiPF ) salt is dissolved in the mixture of carbonate solvents selected from cyclic carbonates - ethylene carbonate (EC), and propylene carbonate (PC) and linear carbonates - dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) -, whose chemical structures are displayed in Fig. 4.2. Recently, another type of liquid electrolyte based on 1.5 M LiBFyy-butyrolactone (GBL) + EC came onto the market for the laminated thin Uthium-ion ceUs with an excellent safety performance. Many other solvents and Uthium salts have limited appUcations, although much effort has been made to develop new materials. Into the above baseline electrolyte solutions, a small amount of the additives are dissolved, which are so-called functional electrolytes. ... 

Functional Electrolytes Specially Designed for Lithium-Ion Batteries... 

UBE has several functional electrolytes requested by customers and is now developing more additives for spinel-based LIB to prevent the corrosion of aluminum substrate and so forth. The main reason for the progress of LIB - e.g., increase in energy density, safety, cyclicity, etc. - is fundamentally due to the development of the functional electrolytes. Even when changing the anode or cathode active material or using the different types of graphite and mixed different types of cathode active material, the different additive compounds should be adopted. This type of LIB cell design is only studied and commercialized by UBE. 

The reason why the progress of gel-polymer battery is rather slow is the slow technological progress in the area of functional electrolytes. The following discussion presents the history of electrolyte and additive development as well as the process followed in the design of LIB electrolyte. 

The solute lithium salt, LiPF, was a common choice for carbonate-based electrolytes and LiBF for y-BL-based electrolytes. In 1994, the method for preparing highly purified LiPF was developed and cleared the way to the use of highly purified solvents and using ad tives. This was a very important step in the rjpid development of a functional electrolytes, hi 2000, novel organic lithium salts of lithium bis-trifluorometh-anesulfonyl imide (HQ115) and lithium bis-pentafluoroethanesulfonyl imide (BETT) were introduced in LIB and marked a new direction for electrolyte development... 

Functional Electrolytes Creation of a Stable Surface for Topochemical Reactions... 

Fig. 19.9 Design diagram for screening electrolyte additives for functional electrolytes...

In general, the LUMO energy values are useful guidelines for compound or additive selection for anode additives, but it is necessary to test the additive compound in practical cell experiments in order to examine the details of the coating film for topochemical reaction. These tests provide important information for the development of the functional electrolytes. Figure 19.14 shows the relationship of the LUMO energy values and reduction potentials of additives on NG or Pt electrode. Reduction potential on NG is higher than those on Pt electrode due to the... 

Third-Generation Functional Electrolytes Designed for Cathode Electrode... 

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