Host structures, insertion materials

For layered host materials as used in the lithium ion cell, the term intercalation is used for the insertion of guests into the host structure. 

The layered arrangement makes these materials very interesting from the point of view of host-guest behaviour because ionic or molecular guest species may be inserted between one layer and another causing the layers to expand or swell. Guest intercalation is generally reversible, and it is an important characteristic of layered solids that, rather like zeolites, they can retain their layered host structure... 

Figures 13 and 14 display the discharge processes for the two kinds of lithium battery. During discharge at the anode the lithium ions are formed from the lithium metal or are released from an Li,A, B < host material at the cathode the lithium ions are inserted into the void spaces of the structure of the A B insertion material. The lithium-ion battery behaves almost like a concentration cell lithium ions move from a lithium-rich source toward the cathode, which acts as sink, while electrons flow through the external circuit from anode to the cathode.

From the position of two given host structures on a redox potential scale such as that in Figure 16 [1, 113, 114], it is possible to determine which material will act as positive electrode and which as negative. For cell design optimization, it has to be taken into account how the basic properties of insertion materials vary as to composition and temperature. For instance, it is useful to determine how the cell voltage depends on the kind of host matrix and the amount of inserted Li". ... 

Interpolation or intercalation seeIntercalation Chemistiy) is said to occur when additional species are placed into a host structure to change either composition or properties. At one extreme, intercalation can refer to the insertion of guest molecules into cage structures such as that of the zeolites see Zeolite, or between the layers of laminated compounds such as the clays see Silicon Inorganic Chemistry. At the other extreme, the insertion of small atoms such as C or N into metal phases to form interstitial alloys see Alloys , Carbides Transition Metal Solid-state Chemistry, Nitrides Transition Metal Sohd-state Chemistry, is included in the category. A large variety of structures can be found in such materials, and... 

The insertion of polymers, with electrical and ionic conductivity, into two-dimensional host structures continues to be a growing field of research in materials science/chemistry. As seen in this review, the technique of intercalation depends on the layered structure that is being investigated. It should also be pointed out that there is a huge repertoire of layered systems that is at the disposal of the researcher, providing the opportunity to create a wide range of nanostructured materials with specific applications. 

LIB electrodes are insertion materials lithium ions travel inside channek of the electrodes and undergo redox reactions with the host structure. The most important insertion materiak are metal oxides. In 1991, Sony commercialized a revolutionary LIB based on a graphite anode and LiCo02 cathode (Figure 36.1). 

A demonstrated method to insert polymer chains into host structures is by in-situ intercalative polymerization of a monomer using the host itself as the oxidant. FeOCl is one of the most convenient redox-intercalation hosts for a great variety of molecules including conducting polymers. The in-situ intercalative polymerization of pyrrole, 2,2 -bithiophene and aniline in the interlayer space of this material has been reported. The resulting intercalation compounds are composed... 

In case the reaction product bears a close structural relationship to the pristine electrode (unreacted) material (H), this type of reaction is classified as topochemical [2]. A special case of the topochemical process is the intercalation or insertion reaction which proceeds without any breakage of bonds in the host structure. This reaction (Eq. 13.1) is generally reversible. 

Insertion (intercalation) compounds. Insertion compounds are defined as products of a reversible reaction of suitable crystalline host materials with guest molecules (ions). Guests are introduced into the host lattice, whose structure is virtually intact except for a possible increase of some lattice constants. This reaction is called topotactic. A special case of topotactic insertion is reaction with host crystals possessing stacked layered structure. In this case, we speak about intercalation (from the Latin verb intercalare, used originally for inserting an extra month, mensis intercalarius, into the calendar). 

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