Nonaqueous electrolyte batteries

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... 

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 ... 

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. 

All lithium based batteries use nonaqueous electrolytes because of the reactivity of lithium in aqueous solution and because of the electrolyte s stability at high voltage. The majority of these cells use microporous membranes made of polyolefins. In some cases, nonwovens made of polyolefins are either used alone or with microporous separators. This section will mainly focus on separators used in secondary lithium batteries followed by a brief summary of separators used in lithium primary batteries. 

The aqueous batteries use water based electrolytes (e.g., KOH electrolyte for NiCd and NiMH and H2-SO4 electrolyte for lead acid), which are less resistive then nonaqueous electrolytes. Polyolefin materials are generally suitable for use in the manufacture of separators for these batteries, but they are not inherently wettable by aqueous electrolytes. Such electrolytes are therefore unable to penetrate the pores of a separator formed from such a material, so that ion migration through the pores in solution will not occur without modification. This problem is sometimes overcome by treating the polyolefin material with a surfactant, which allows an aqueous electrolyte to wet the material. However, such surfactant can be removed from the surfaces of the polyolefin material when electrolyte is lost from the device, for example during charging and discharging cycles, and it is not subsequently replaced on the material when the electrolyte is replenished. 

Minor admixtures of water to nonaqueous electrolytes are often harmful, for example in batteries with inorganic solvents such as POCI3, SOCI2, SO2CI2, where it is important that the electrolyte be free of water contamination because of the possible formation of oxychloride cements ... 

Another approach is to use a lithium/sulfur cell with nonaqueous electrolyte systems. Rechargeable lithium batteries are being developed for portable power applications such as electric vehicles, partly because of their specific energy ranges 100-150 Wh kg (and... 

Acetonitrile has been selected as the solvent in this study since it is a possible candidate for a nonaqueous electrolyte battery (5). From this viewpoint, acetonitrile has several attractive physical properties, as shown in Table I. It has a useful liquid state range and a reasonably low vapor pressure and viscosity at ambient temperature. In addition, many common electrolytes are soluble in acetonitrile. Acetonitrile is a good model solvent for solvation studies, as the molecule is a linear aprotic dipole. 

This chapter deals primarily with reactions in aqueous media, but the principles can be extended to fuel cells and other batteries like the high-temperature batteries with exotic nonaqueous electrolytes. 

Lithium cyclodifluoromethane-l,l-bis(sulfonyl)imide 150 found an application as a conductive salt in nonaqueous electrolytes for lithium secondary batteries. The corresponding battery cells showed outstanding properties in respect to the capacity and the constant voltage <1997WO9731909>. 

Needless to say that a deep understanding of both the formation mechanism of the SEI layer and the underlaying question of carbon s surface chemistry in a particular electrolyte solution is of utmost importance for battery developers. Clearly, the surface chemistry of graphite electrodes plays a key role in their performance.259 312 325 343-352 A lot of work was devoted to decipher this very complicated surface chemistry. It is therefore not surprising that the advancement in the understanding of surface chemistry of carbon electrodes in nonaqueous electrolytes correlates well with the worldwide production rate of lithium-ion batteries. 

Usually, in a given electrolyte solution, there is a similarity in the mechanism of SEI formation on carbon and metallic lithium.285 353 354 The mechanisms of SEI formation on lithium in numerous electrolytes are investigated since about three decades. In about the last 15 years, the focus continuously shifted from metallic lithium to carbon. There are a huge number of publications covering manifold aspects of the carbon s reactivity with the electrolytes and/or the SEI formation. The reader of this chapter is referred to the books published in this field recently and especially to the primary literature listed therein. Examples include Nonaqueous Electrochemistry from 1999 edited by Aurbach,355 Advances in Lithium-Ion Batteries from 2002 edited by van Schalkwijk and Scrosati,356 and Lithium-Ion Batteries Solid-Electrolyte Interphase from 2004 edited by Balbuena and Wang.281... 

High energy density batteries are a crucial need as modern electronics progresses and moves more and more toward miniaturization. Many novel battery systems require the use of nonaqueous electrolyte systems because important new developments in this field are based on active metal electrodes (eg, Li and Li-C intercalation compounds). 

Extensive studies on conductivity and related parameters of nonaqueous electrolyte solutions have been carried out in connection with lithium batteries, due to the importance of lowering their internal resistance, power losses, and the consequent heat dissipation, during operation. Tables 5-8 present some typical data on the conductivity of nonaqueous electrolyte solutions [38-44],... 

The nonaqueous electrolyte systems mentioned in this section are solid state systems which may be very important and promising for some types of batteries and fuel cells applications. 

A major part of the work with nonaqueous electrolyte solutions in modern electrochemistry relates to the field of batteries. Many important kinds of novel, high energy density batteries are based on highly reactive anodes, especially lithium, Li alloys, and lithiated carbons, in polar aprotic electrolyte systems. In fact, a great part of the literature related to nonaqueous electrolyte solutions which has appeared during the past two decades is connected to lithium batteries. These facts justify the dedication of a separate chapter in this book to the electrochemical behavior of active metal electrodes. 

In the case of ion conductive polymers, gel polymer electrolytes which consist of a polymer matrix, organic solvents and supporting electrolyte, were introduced as novel nonaqueous electrolyte systems in electrochemical applications, such as rechargeable batteries and electric double layer capacitors [3-5], Recently, considerable attention has been devoted to the application of gel poly-... 

Refs. [i] Aurbach D, Weissman (1999) Nonaqueous electrochemistry an overview. In Aurbach D (ed) Nonaqueous electrochemistry. Marcel Dekker, New York, pp 1-52 [ii] Blomgren GE (1999) Physical and chemical properties of nonaqueous electrolyte solutions. In Aurbach D (ed) Nonaqueous electrochemistry. Marcel Dekker, New York, pp 53-58 [iii] Izutsu K (2002) Electrochemistry in nonaqueous solutions. Wiley-VCH, Weinheim, pp 3-24 [iv] Lund H (2001) Practical problems in electrolysis. In Lund H, Hammerich O (eds) Organic electrochemistry, 4th edn. Marcel Dekker, New York, pp 223-292 [v] Linden D (1994) Handbook of batteries, 2nd edn. McGraw-Hill, New York, Appendix A... 

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). 

Fig. 1. Schematic illustration for a rechargeable lithium ion battery with LiCoO, cathode, graphite anode and nonaqueous electrolyte.

Ionic conductivities of various aqueous and nonaqueous electrolytes used in rechargeable batteries... 

---