Positive electrode materials phosphates

Positive electrode materials available for Li ion cells today include metal oxide or phosphate compounds, such as... 

Nakayama M, Goto S, Uchimoto Y, WaMhara M, Kitayama Y (2004) Changes in electronic structure between cobalt and oxide ions of lithium cobalt phosphate as 4.8-V positive electrode material. Chem Mater 16 3399-3401... 

The metal oxides used to make positive electrode materials for lithium-ion batteries commonly include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, vanadium oxide, and various others, such as iron oxides. Positive electrode materials of 5 V and polyanion-type positive electrode materials (so far mainly referring to lithium iron phosphate, LiFeP04) have also been investigated. Among the primary materials for these positive electrode materials, cobalt is the most expensive, followed by nickel and then manganese and vanadium. As a result, the prices of positive electrode materials are basically in line with the market prices of the primary materials. The structures of these positive electrode materials are mainly layered, spinel, and oliven. 

Lithium ferrous(II) phosphate (LiFeP04) is a positive electrode material for lithium-ion batteries, which, so far, has been mainly used in power lithium-ion batteries [1]. It is commonly called lithium iron(II) phosphate and is also used in fertilizers. In 1996, the Japanese NTT Corporation disclosed for the first time an olivine structured compound, A MP04 (A is an alkali metal and M a combination of Co and Fe) as a positive electrode material for lithium-ion batteries. In 1997, Prof. John B. Goodenough and his group at the University of Texas at Austin, United States, reported the characteristics of reversible lithium intercalation/deintercalation into/from LiFeP04. However, at the initial stage, this positive electrode material did not raise much attention since its electronic and ionic conductivities are very low and... 

The main positive electrode materials for lithium-ion batteries, LiCo02, LiNi02, LiMn204, and LiFeP04, were discussed in Chapters 2 through 5. In this chapter, several other important positive electrode materials will be discussed, including Li-rich layered Mn oxides, phosphates, sulfates, silicates, borates, titanates, V2O5, and other oxides [1]. 

The crossover of methanol has caused problems in finding a suitable membrane material. On the positive electrode side, methanol combines with oxygen to form CO2. Among the alternatives to pure Nafion are Nafion filled with zirconium phosphate or grafted with styrene to inhibit methanol transport (Bauer and Willert-Porada, 2003 Sauk et al., 2004), as well as non-Nafion membrane materials such as sulfonated polyimide (Woo et al., 2003). None have achieved performance as good as the one shown in Fig. 3.53, which, however, has a substantial methanol crossover rate. 

As discussed in Chapter 5, LiFeP04 is a widely used phosphate positive electrode. In this section, other kinds of phosphates, mostly based on LiMnP04, are discussed. The complex phosphate Li3Fe2(P04)3 has a sodium (Na) Super Ionic CONductor (NASICON) structure. The cyclic voltammogram ( ) curve shows two plateaus during the charge and discharge processes, at 2.80 and 2.65 V, with a reversible capacity of up to 1.5-1.6 Li per unit. Since very little is known about this material, it will not be discussed further. 

Trimethylhydroxylysine (THL) and its phosphate (THLP) These two derivatives have been identified in proteinacious material from cell walls of diatoms (Nakajima and Volcani 1970). In pH 1.9 electrophoresis they migrate 2.4 cm (THLP) and 6.1 cm (THL) towards the negative electrode, respectively, at 33.3 volts/cm for 20 min. In the analyzer system of Dus et al. (1966), THLP elutes in about the same position as threonine, and THL elutes between NH3 and arginine (a buffer peak also elutes in this region). In the complex analyzer system of Hamilton (1963), THLP elutes at a volume about 2.4 times that of cysteic acid and 0.58 that of aspartic acid. 

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