Olivine phosphate cathode materials

Olivine Phosphate Cathode Materials, Reactivity and Reaction Mechanisms... 

Phospho-olivines as lithium intercalation materials were reported early in 1997. Unfortunately, researchers did not pay much attention to them because olivine phosphates with low electronic conductivity did not allow most of the lithium ions to intercalate/de-intercalate reversibly. This low reversibility could lead to low capacity, particularly at high current densities. Under the strong driving force of safety requirements when lithium ion batteries are used commercially for both portable devices and EV/HEV applications, olivine phosphate cathode materials, especially LiFeP04, have been revisited globally by researchers since the beginning of the 2F century. Attractive features are... 

Reversible electrochemical lithium deintercalation from 2D and 3D materials is important for applications in lithium-ion batteries. New developments have been realized in two classes of materials that show exceptionally promising properties as cathode materials. The first includes mixed layered oxides exemplified by LijMn Nij, Co ]02, where the Mn remains inert to oxidation/reduction and acts as a framework stabilizer while the other elements carry the redox load. Another class that shows much potential is metal phosphates, which includes olivine-type LiFeP04, and the NASICON-related frameworks Li3M2(P04)3. 

Based on their structure, cathodes can be separated into three basic families layered oxides, spinels, and olivine phosphates. The three families differ greatly in their cell performance as well as in thermal properties. Layered oxide cathodes typically have higher specific capacities than spinels or phosphates. As a consequence of their structure, layered oxide materials are more energetic upon thermal runaway events due to the ease with which oxygen is liberated from their framework upon decomposition. 

In the last two decades, compounds with different polyanion groups such as phosphates (P04 ), pyrophosphates (P2O7" ), silicates(Si04" ), sulfates(S04 ), borates (B03 ) as well as their lluorinated compounds have been widely investigated in the literature. In this chapter, some recent studies of polyanion compounds for use in Li-ion batteries are introduced and summarized. Some review papers in this field can also be found in the literature [5, 6]. Here, we mainly focus on the different polyanion compounds in use as cathode materials, except for olivine-type LiFeP04 and its analogues. 

In the search of new cathodes, parhcular attention is addressed to materials of the olivine family and, in particular, on lithium iron phosphate, LiFeP04 [29]. This interest is motivated by the many appealing features of this com-poxmd, which include good capacity (170 mAh g i), a two-phase electrochemical process that evolves with a flat 3.5 V vs. Li voltage (see Figure 3.23),... 

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