Lithium using solid electrolytes

Li2S204 being the SEI component at the Li anode and the solid discharge product at the carbon cathode. The Li—SOCI2 and Li—SO2 systems have excellent operational characteristics in a temperature range from —40 to 60 °C (SOCI2) or 80 °C (SO2). Typical applications are military, security, transponder, and car electronics. Primary lithium cells have also various medical uses. The lithium—silver—vanadium oxide system finds application in heart defibrillators. The lithium—iodine system with a lithium iodide solid electrolyte is the preferred pacemaker cell. 

West WC, Whitacre JF, Lim JR. Chemical stability enhancement of lithium conducting solid electrolyte plates using sputtered LiPON thin films. J Power Sources. 2004 126(1-2) 134-8. 

Lithium is the most electropositive metal and the lightest consequently there has been a lot of interest in electrochemical devices using components that include Li metal electrodes and Li+ conducting solid electrolytes. Hundreds of materials have been studied for applications as potential lithium conducting solid electrolytes. Tables 1 and 2 give representative examples of the more important Li+ solid electrolytes, some of which are discussed in this section. 

Solid electrolyte lithium batteries have been produced for low-drain applications. The Catalyst Research Corporation produce a lithium-iodine solid electrolyte system, rated at 20,uA for heart pacemaker use. 

A possible solution to this problem is to use an electrolyte, such as a solid polymer electrolyte, which is less reactive with lithium metal [3]. Another simple solution is the lithium-ion cell. 

In practice, for a ternary system, the decomposition voltage of the solid electrolyte may be readily measured with the help of a galvanic cell which makes use of the solid electrolyte under investigation and the adjacent equilibrium phase in the phase diagram as an electrode. A convenient technique is the formation of these phases electrochemically by decomposition of the electrolyte. The sample is polarized between a reversible electrode and an inert electrode such as Pt or Mo in the case of a lithium ion conductor, in the same direction as in polarization experiments. The... 

The sol-gel technique was also used to prepare solid electrolytes containing MEEP, triethoxysilane (TEOS) and lithium triflate. Homogeneous, transparent and mechanicaUy stable materials have been obtained by Gughelmi [611] from a partially hydroxylated MEEP and TEOS, which after doping with LiSOjCFj exhibited a conductivity in the range 3x10 S cm at 60 °C. 

Fig. 11.7 Schematic diagram of an all-solid state lithium-air battery using lithium anode, an inorganic solid electrolyte, and an air electrode composed of carbon nanotubes and solid electrolyte particles. Reprinted with permission from Hirokazu Kitaura etai, Energy Environ. Sci., 2012, 5,...

Lithium secondary batteries can be classified into three types, a liquid type battery using liquid electrolytes, a gel type battery using gel electrolytes mixed with polymer and liquid, and a solid type battery using polymer electrolytes. The types of separators used in different types of secondary lithium batteries are shown in Table 1. The liquid lithium-ion cell uses microporous polyolefin separators while the gel polymer lithium-ion cells either use a PVdF separator (e.g. PLION cells) or PVdF coated microporous polyolefin separators. The PLION cells use PVdF loaded with silica and plasticizer as separator. The microporous structure is formed by removing the plasticizer and then filling with liquid electrolyte. They are also characterized as plasticized electrolyte. In solid polymer lithium-ion cells, the solid electrolyte acts as both electrolyte and separator. 

Development efforts are under way to displace the use of microporous membranes as battery separators and instead use gel electrolytes or polymer electrolytes. Polymer electrolytes, in particular, promise enhanced safety by eliminating organic volatile solvents. The next two sections are devoted to solid polymer and gel polymer type lithium-ion cells with focus on their separator/electrolyte requirements. 

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